Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

105 files changed, 13530 insertions, 0 deletions

diff --git a/src/boost/libs/yap/CMakeLists.txt b/src/boost/libs/yap/CMakeLists.txt
new file mode 100644
index 00000000..98a23b2f
--- /dev/null
+++ b/src/boost/libs/yap/CMakeLists.txt
@@ -0,0 +1,120 @@
+cmake_minimum_required(VERSION 3.5)
+list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
+
+################################################## 
+# C++ standard version selection
+################################################## 
+function(constexpr_if_std std_flag var)
+    try_compile(
+        worked
+        ${CMAKE_BINARY_DIR}
+        ${CMAKE_CURRENT_SOURCE_DIR}/cmake/constexpr_if.cpp
+        COMPILE_DEFINITIONS ${std_flag} -DCHECK_CONSTEXPR_IF=1
+    )
+    set(${var} ${worked} PARENT_SCOPE)
+endfunction ()
+
+function(try_std_flag std_flag)
+    try_compile(
+        std_supported
+        ${CMAKE_BINARY_DIR}
+        ${CMAKE_CURRENT_SOURCE_DIR}/cmake/constexpr_if.cpp
+        COMPILE_DEFINITIONS ${std_flag} -DCHECK_CONSTEXPR_IF=0
+    )
+    if (std_supported)
+        message("-- Checking compiler flag ${std_flag} -- success")
+        set(std_flag ${std_flag} PARENT_SCOPE)
+        constexpr_if_std(${std_flag} have_constexpr_if)
+        if (have_constexpr_if)
+            set(constexpr_if_define -DBOOST_NO_CONSTEXPR_IF=0 PARENT_SCOPE)
+            message("-- Checking constexpr if support -- success")
+        else ()
+            set(constexpr_if_define -DBOOST_NO_CONSTEXPR_IF=1 PARENT_SCOPE)
+            message("-- Checking constexpr if support -- failed to compile")
+        endif ()
+    else ()
+        message("-- Checking compiler flag ${std_flag} -- failed to compile")
+    endif ()
+endfunction ()
+
+try_std_flag(-std=c++17)
+if (NOT std_flag)
+    try_std_flag(-std=c++1z) 
+elseif (NOT std_flag)
+    try_std_flag(-std=c++14)
+elseif (NOT std_flag)
+    try_std_flag(/std:c++14)
+elseif (NOT std_flag)
+    message(FATAL_ERROR "Only c++14 or later will work")
+endif ()
+
+##################################################
+# Sanitizers
+##################################################
+set(USE_ASAN false CACHE BOOL "Set to true to enable -fsanitize=address when building tests.") 
+set(USE_UBSAN false CACHE BOOL "Set to true to enable -fsanitize=undefined when building tests.")
+if (USE_ASAN AND USE_UBSAN)
+    message(FATAL_ERROR "USE_ASAN and USE_UBSAN must not be enabled at the same time")
+elseif (USE_ASAN)
+    set(compile_flags -fsanitize=address)
+    set(link_flags -fsanitize=address)
+    message("-- Using -fsanitize=address") 
+elseif (USE_UBSAN)
+    set(compile_flags -fsanitize=undefined)
+    set(link_flags -fsanitize=undefined)
+    message("-- Using -fsanitize=undefined")
+endif()
+
+##################################################
+# Code coverage
+##################################################
+if (UNIX)
+    set(BUILD_COVERAGE false CACHE BOOL "Set to true to enable code coverage when building tests.  Only Linux and Mac are supported.")
+    if (BUILD_COVERAGE)
+        message("-- Building for code coverage; disabling any sanitizers")
+        if (APPLE)
+            set(compile_flags -fprofile-arcs -ftest-coverage)
+            set(CMAKE_BUILD_TYPE RelWithDebInfo)
+            set(link_flags --coverage)
+        else ()
+            set(compile_flags --coverage)
+            set(CMAKE_BUILD_TYPE RelWithDebInfo)
+            set(link_flags --coverage)
+        endif ()
+    endif ()
+endif ()
+
+##################################################
+# Clang+Linux support
+##################################################
+set(clang_on_linux false)
+if (CMAKE_CXX_COMPILER_ID STREQUAL Clang)
+    add_definitions(${std_flag} -stdlib=libc++ -g -Wall)
+    if (CMAKE_SYSTEM_NAME STREQUAL Linux)
+        set(clang_on_linux true)
+    endif ()
+elseif (CMAKE_CXX_COMPILER_ID STREQUAL GNU)
+    add_definitions(${std_flag} -g -Wall)
+endif ()
+
+##################################################
+# Dependencies
+##################################################
+include(dependencies)
+
+##################################################
+# yap library
+##################################################
+add_library(yap INTERFACE)
+target_include_directories(yap INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include)
+target_link_libraries(yap INTERFACE boost)
+target_compile_definitions(yap INTERFACE ${constexpr_if_define} BOOST_ALL_NO_LIB=1)
+if (link_flags)
+    target_link_libraries(yap INTERFACE ${link_flags})
+    target_compile_options(yap INTERFACE ${compile_flags})
+endif ()
+
+add_subdirectory(test)
+add_subdirectory(example)
+add_subdirectory(perf)
+add_subdirectory(doc) # Doesn't build docs, just the snippets files.
diff --git a/src/boost/libs/yap/LICENSE_1_0.txt b/src/boost/libs/yap/LICENSE_1_0.txt
new file mode 100644
index 00000000..36b7cd93
--- /dev/null
+++ b/src/boost/libs/yap/LICENSE_1_0.txt
@@ -0,0 +1,23 @@
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/src/boost/libs/yap/README.md b/src/boost/libs/yap/README.md
new file mode 100644
index 00000000..ce6b8be3
--- /dev/null
+++ b/src/boost/libs/yap/README.md
@@ -0,0 +1,11 @@
+[![Build Status](https://travis-ci.org/boostorg/yap.svg?branch=master)](https://travis-ci.org/boostorg/yap)
+[![codecov](https://codecov.io/gh/tzlaine/yap/branch/master/graph/badge.svg)](https://codecov.io/gh/tzlaine/yap)
+[![License](https://img.shields.io/badge/license-boost-brightgreen.svg)](LICENSE_1_0.txt)
+
+
+# yap
+A C++14-and-later expression template library
+
+This is a Boost library.  It covers the same problem space as Boost.Proto, but works quite differently, due to the availability of lots of new features in C++14 and later.
+
+Please read the docs for details: https://boostorg.github.io/yap
diff --git a/src/boost/libs/yap/cmake/Disassemble.cmake b/src/boost/libs/yap/cmake/Disassemble.cmake
new file mode 100644
index 00000000..93f6e9a5
--- /dev/null
+++ b/src/boost/libs/yap/cmake/Disassemble.cmake
@@ -0,0 +1,71 @@
+# Copyright Louis Dionne 2016
+# Copyright Zach Laine 2016
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+#
+#
+# This CMake module provides a way to get the disassembly of a function within
+# an executable created with `add_executable`. The module provides a `disassemble`
+# function that creates a target which, when built, outputs the disassembly of
+# the given function within an executable to standard output.
+#
+# Parameters
+# ----------
+# target:
+#   The name of the target to create. Building this target will generate the
+#   requested disassembly.
+#
+# EXECUTABLE executable:
+#   The name of an executable to disassemble. This must be the name of a valid
+#   executable that was created with `add_executable`. The disassembly target
+#   thus created will be made dependent on the executable, so that it is built
+#   automatically when the disassembly is requested.
+#
+# FUNCTION function-name:
+#   The name of the function to disassemble in the executable.
+#
+# [ALL]:
+#   If provided, the generated target is included in the 'all' target.
+#
+function(disassemble target)
+  cmake_parse_arguments(ARGS "ALL"                 # options
+                             "EXECUTABLE;FUNCTION" # 1 value args
+                             ""                    # multivalued args
+                             ${ARGN})
+
+  if (NOT ARGS_EXECUTABLE)
+    message(FATAL_ERROR "The `EXECUTABLE` argument must be provided.")
+  endif()
+  if (NOT TARGET ${ARGS_EXECUTABLE})
+    message(FATAL_ERROR "The `EXECUTABLE` argument must be the name of a valid "
+                        "executable created with `add_executable`.")
+  endif()
+
+  if (NOT ARGS_FUNCTION)
+    message(FATAL_ERROR "The `FUNCTION` argument must be provided.")
+  endif()
+
+  if (ARGS_ALL)
+    set(ARGS_ALL "ALL")
+  else()
+    set(ARGS_ALL "")
+  endif()
+
+  if (DISASSEMBLE_lldb)
+    add_custom_target(${target} ${ARGS_ALL}
+      COMMAND ${DISASSEMBLE_lldb} -f $<TARGET_FILE:${ARGS_EXECUTABLE}>
+                                  -o "disassemble --name ${ARGS_FUNCTION}"
+                                  -o quit
+      DEPENDS ${ARGS_EXECUTABLE}
+    )
+  elseif(DISASSEMBLE_gdb)
+    add_custom_target(${target} ${ARGS_ALL}
+      COMMAND ${DISASSEMBLE_gdb} -batch -se $<TARGET_FILE:${ARGS_EXECUTABLE}>
+                                 -ex "disassemble ${ARGS_FUNCTION}"
+      DEPENDS ${ARGS_EXECUTABLE}
+    )
+  endif()
+endfunction()
+
+find_program(DISASSEMBLE_gdb gdb)
+find_program(DISASSEMBLE_lldb lldb)
diff --git a/src/boost/libs/yap/cmake/constexpr_if.cpp b/src/boost/libs/yap/cmake/constexpr_if.cpp
new file mode 100644
index 00000000..be6ca37f
--- /dev/null
+++ b/src/boost/libs/yap/cmake/constexpr_if.cpp
@@ -0,0 +1,13 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+int main ()
+{
+#if CHECK_CONSTEXPR_IF
+    if constexpr (true) {
+        return 0;
+    }
+#endif
+}
diff --git a/src/boost/libs/yap/cmake/dependencies.cmake b/src/boost/libs/yap/cmake/dependencies.cmake
new file mode 100644
index 00000000..b246e887
--- /dev/null
+++ b/src/boost/libs/yap/cmake/dependencies.cmake
@@ -0,0 +1,68 @@
+# Copyright Louis Dionne 2016
+# Copyright Zach Laine 2016
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+###############################################################################
+# Boost
+###############################################################################
+find_package(Boost COMPONENTS)
+if (Boost_INCLUDE_DIRS)
+  add_library(boost INTERFACE)
+  target_include_directories(boost INTERFACE ${Boost_INCLUDE_DIRS})
+else ()
+  message("-- Boost was not found; attempting to download it if we haven't already...")
+  include(ExternalProject)
+  ExternalProject_Add(install-Boost
+    PREFIX ${CMAKE_BINARY_DIR}/dependencies/boost_1_68_0
+    URL https://dl.bintray.com/boostorg/release/1.68.0/source/boost_1_68_0.tar.bz2
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND ""
+    INSTALL_COMMAND ""
+    LOG_DOWNLOAD ON
+  )
+
+  ExternalProject_Get_Property(install-Boost SOURCE_DIR)
+  add_library(boost INTERFACE)
+  target_include_directories(boost INTERFACE ${SOURCE_DIR})
+  add_dependencies(boost install-Boost)
+  unset(SOURCE_DIR)
+endif ()
+
+
+###############################################################################
+# Google Benchmark
+###############################################################################
+execute_process(
+    COMMAND git clone https://github.com/google/benchmark.git
+    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+)
+execute_process(
+    COMMAND git checkout v1.2.0
+    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/benchmark
+)
+
+option(BENCHMARK_ENABLE_TESTING "Enable testing of the benchmark library." OFF)
+add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/benchmark)
+
+
+###############################################################################
+# Autodiff (see https://github.com/fqiang/autodiff_library)
+###############################################################################
+add_library(autodiff_library
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/ActNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/BinaryOPNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/Edge.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/EdgeSet.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/Node.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/OPNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/PNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/Stack.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/Tape.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/UaryOPNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/VNode.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library/autodiff.cpp
+)
+target_include_directories(autodiff_library PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/example/autodiff_library)
+target_compile_definitions(autodiff_library PUBLIC BOOST_ALL_NO_LIB=1)
+target_link_libraries(autodiff_library boost)
diff --git a/src/boost/libs/yap/example/CMakeLists.txt b/src/boost/libs/yap/example/CMakeLists.txt
new file mode 100644
index 00000000..434ff12b
--- /dev/null
+++ b/src/boost/libs/yap/example/CMakeLists.txt
@@ -0,0 +1,43 @@
+include_directories(${CMAKE_HOME_DIRECTORY})
+
+include(CTest)
+
+enable_testing()
+
+add_custom_target(run_examples COMMAND ${CMAKE_CTEST_COMMAND} -VV -C ${CMAKE_CFG_INTDIR})
+
+macro(add_sample name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name} yap)
+    add_test(${name} ${CMAKE_CURRENT_BINARY_DIR}/${name})
+    if (clang_on_linux)
+        target_link_libraries(${name} c++)
+    endif ()
+endmacro()
+
+add_sample(minimal)
+add_sample(hello_world)
+add_sample(hello_world_redux)
+add_sample(calc1)
+add_sample(calc2a)
+add_sample(calc2b)
+add_sample(calc3)
+add_sample(lazy_vector)
+add_sample(tarray)
+add_sample(vec3)
+add_sample(vector)
+add_sample(mixed)
+add_sample(map_assign)
+add_sample(future_group)
+add_sample(transform_terminals)
+add_sample(pipable_algorithms)
+if (constexpr_if_define STREQUAL "-DBOOST_NO_CONSTEXPR_IF=0")
+    add_sample(let)
+    add_sample(self_evaluation)
+endif ()
+
+add_executable(autodiff autodiff_example.cpp)
+target_link_libraries(autodiff yap boost autodiff_library)
+if (clang_on_linux)
+    target_link_libraries(autodiff c++)
+endif ()
diff --git a/src/boost/libs/yap/example/autodiff_example.cpp b/src/boost/libs/yap/example/autodiff_example.cpp
new file mode 100644
index 00000000..597a4094
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_example.cpp
@@ -0,0 +1,852 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include "autodiff.h"
+
+#include <iostream>
+
+#include <boost/yap/algorithm.hpp>
+#include <boost/polymorphic_cast.hpp>
+#include <boost/hana/for_each.hpp>
+
+#define BOOST_TEST_MODULE autodiff_test
+#include <boost/test/included/unit_test.hpp>
+
+
+double const Epsilon = 10.0e-6;
+#define CHECK_CLOSE(A,B) do { BOOST_CHECK_CLOSE(A,B,Epsilon); } while(0)
+
+using namespace AutoDiff;
+
+//[ autodiff_expr_template_decl
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct autodiff_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_UNARY_OPERATOR(negate, autodiff_expr, autodiff_expr)
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, autodiff_expr, autodiff_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, autodiff_expr, autodiff_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(multiplies, autodiff_expr, autodiff_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(divides, autodiff_expr, autodiff_expr)
+//]
+
+//[ autodiff_expr_literals_decl
+namespace autodiff_placeholders {
+
+    // This defines a placeholder literal operator that creates autodiff_expr
+    // placeholders.
+    BOOST_YAP_USER_LITERAL_PLACEHOLDER_OPERATOR(autodiff_expr)
+
+}
+//]
+
+//[ autodiff_function_terminals
+template <OPCODE Opcode>
+struct autodiff_fn_expr :
+    autodiff_expr<boost::yap::expr_kind::terminal, boost::hana::tuple<OPCODE>>
+{
+    autodiff_fn_expr () :
+        autodiff_expr {boost::hana::tuple<OPCODE>{Opcode}}
+    {}
+
+    BOOST_YAP_USER_CALL_OPERATOR_N(::autodiff_expr, 1);
+};
+
+// Someone included <math.h>, so we have to add trailing underscores.
+autodiff_fn_expr<OP_SIN> const sin_;
+autodiff_fn_expr<OP_COS> const cos_;
+autodiff_fn_expr<OP_SQRT> const sqrt_;
+//]
+
+//[ autodiff_xform
+struct xform
+{
+    // Create a var-node for each placeholder when we see it for the first
+    // time.
+    template <long long I>
+    Node * operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                       boost::yap::placeholder<I>)
+    {
+        if (list_.size() < I)
+            list_.resize(I);
+        auto & retval = list_[I - 1];
+        if (retval == nullptr)
+            retval = create_var_node();
+        return retval;
+    }
+
+    // Create a param-node for every numeric terminal in the expression.
+    Node * operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>, double x)
+    { return create_param_node(x); }
+
+    // Create a "uary" node for each call expression, using its OPCODE.
+    template <typename Expr>
+    Node * operator() (boost::yap::expr_tag<boost::yap::expr_kind::call>,
+                       OPCODE opcode, Expr const & expr)
+    {
+        return create_uary_op_node(
+            opcode,
+            boost::yap::transform(boost::yap::as_expr<autodiff_expr>(expr), *this)
+        );
+    }
+
+    template <typename Expr>
+    Node * operator() (boost::yap::expr_tag<boost::yap::expr_kind::negate>,
+                       Expr const & expr)
+    {
+        return create_uary_op_node(
+            OP_NEG,
+            boost::yap::transform(boost::yap::as_expr<autodiff_expr>(expr), *this)
+        );
+    }
+
+    // Define a mapping from binary arithmetic expr_kind to OPCODE...
+    static OPCODE op_for_kind (boost::yap::expr_kind kind)
+    {
+        switch (kind) {
+        case boost::yap::expr_kind::plus: return OP_PLUS;
+        case boost::yap::expr_kind::minus: return OP_MINUS;
+        case boost::yap::expr_kind::multiplies: return OP_TIMES;
+        case boost::yap::expr_kind::divides: return OP_DIVID;
+        default: assert(!"This should never execute"); return OPCODE{};
+        }
+        assert(!"This should never execute");
+        return OPCODE{};
+    }
+
+    // ... and use it to handle all the binary arithmetic operators.
+    template <boost::yap::expr_kind Kind, typename Expr1, typename Expr2>
+    Node * operator() (boost::yap::expr_tag<Kind>, Expr1 const & expr1, Expr2 const & expr2)
+    {
+        return create_binary_op_node(
+            op_for_kind(Kind),
+            boost::yap::transform(boost::yap::as_expr<autodiff_expr>(expr1), *this),
+            boost::yap::transform(boost::yap::as_expr<autodiff_expr>(expr2), *this)
+        );
+    }
+
+    vector<Node *> & list_;
+};
+//]
+
+//[ autodiff_to_node
+template <typename Expr, typename ...T>
+Node * to_auto_diff_node (Expr const & expr, vector<Node *> & list, T ... args)
+{
+    Node * retval = nullptr;
+
+    // This fills in list as a side effect.
+    retval = boost::yap::transform(expr, xform{list});
+
+    assert(list.size() == sizeof...(args));
+
+    // Fill in the values of the value-nodes in list with the "args"
+    // parameter pack.
+    auto it = list.begin();
+    boost::hana::for_each(
+        boost::hana::make_tuple(args ...),
+        [&it](auto x) {
+            Node * n = *it;
+            VNode * v = boost::polymorphic_downcast<VNode *>(n);
+            v->val = x;
+            ++it;
+        }
+    );
+
+    return retval;
+}
+//]
+
+struct F{
+	F() {	AutoDiff::autodiff_setup();	}
+	~F(){	AutoDiff::autodiff_cleanup();	}
+};
+
+
+BOOST_FIXTURE_TEST_SUITE(all, F)
+
+//[ autodiff_original_node_builder
+Node* build_linear_fun1_manually(vector<Node*>& list)
+{
+	//f(x1,x2,x3) = -5*x1+sin(10)*x1+10*x2-x3/6
+	PNode* v5 = create_param_node(-5);
+	PNode* v10 = create_param_node(10);
+	PNode* v6 = create_param_node(6);
+	VNode*	x1 = create_var_node();
+	VNode*	x2 = create_var_node();
+	VNode*	x3 = create_var_node();
+
+	OPNode* op1 = create_binary_op_node(OP_TIMES,v5,x1);   //op1 = v5*x1
+	OPNode* op2 = create_uary_op_node(OP_SIN,v10);         //op2 = sin(v10)
+	OPNode* op3 = create_binary_op_node(OP_TIMES,op2,x1);  //op3 = op2*x1
+	OPNode* op4 = create_binary_op_node(OP_PLUS,op1,op3);  //op4 = op1 + op3
+	OPNode*	op5 = create_binary_op_node(OP_TIMES,v10,x2);  //op5 = v10*x2
+	OPNode* op6 = create_binary_op_node(OP_PLUS,op4,op5);  //op6 = op4+op5
+	OPNode* op7 = create_binary_op_node(OP_DIVID,x3,v6);   //op7 = x3/v6
+	OPNode* op8 = create_binary_op_node(OP_MINUS,op6,op7); //op8 = op6 - op7
+	x1->val = -1.9;
+	x2->val = 2;
+	x3->val = 5./6.;
+	list.push_back(x1);
+	list.push_back(x2);
+	list.push_back(x3);
+	return op8;
+}
+//]
+
+//[ autodiff_yap_node_builder
+Node* build_linear_fun1(vector<Node*>& list)
+{
+    //f(x1,x2,x3) = -5*x1+sin(10)*x1+10*x2-x3/6
+    using namespace autodiff_placeholders;
+    return to_auto_diff_node(
+        -5 * 1_p + sin_(10) * 1_p + 10 * 2_p - 3_p / 6,
+        list,
+        -1.9,
+        2,
+        5./6.
+    );
+}
+//]
+
+Node* build_linear_function2_manually(vector<Node*>& list)
+{
+	//f(x1,x2,x3) = -5*x1+-10*x1+10*x2-x3/6
+	PNode* v5 = create_param_node(-5);
+	PNode* v10 = create_param_node(10);
+	PNode* v6 = create_param_node(6);
+	VNode*	x1 = create_var_node();
+	VNode*	x2 = create_var_node();
+	VNode*	x3 = create_var_node();
+	list.push_back(x1);
+	list.push_back(x2);
+	list.push_back(x3);
+	OPNode* op1 = create_binary_op_node(OP_TIMES,v5,x1); //op1 = v5*x1
+	OPNode* op2 = create_uary_op_node(OP_NEG,v10);       //op2 = -v10
+	OPNode* op3 = create_binary_op_node(OP_TIMES,op2,x1);//op3 = op2*x1
+	OPNode* op4 = create_binary_op_node(OP_PLUS,op1,op3);//op4 = op1 + op3
+	OPNode*	op5 = create_binary_op_node(OP_TIMES,v10,x2);//op5 = v10*x2
+	OPNode* op6 = create_binary_op_node(OP_PLUS,op4,op5);//op6 = op4+op5
+	OPNode* op7 = create_binary_op_node(OP_DIVID,x3,v6); //op7 = x3/v6
+	OPNode* op8 = create_binary_op_node(OP_MINUS,op6,op7);//op8 = op6 - op7
+	x1->val = -1.9;
+	x2->val = 2;
+	x3->val = 5./6.;
+	return op8;
+}
+
+Node* build_linear_function2(vector<Node*>& list)
+{
+    //f(x1,x2,x3) = -5*x1+-10*x1+10*x2-x3/6
+    using namespace autodiff_placeholders;
+    auto ten = boost::yap::make_terminal<autodiff_expr>(10);
+    return to_auto_diff_node(
+        -5 * 1_p + -ten * 1_p + 10 * 2_p - 3_p / 6,
+        list,
+        -1.9,
+        2,
+        5./6.
+    );
+}
+
+Node* build_nl_function1_manually(vector<Node*>& list)
+{
+//	(x1*x2 * sin(x1))/x3 + x2*x4 - x1/x2
+	VNode* x1 = create_var_node();
+	VNode* x2 = create_var_node();
+	VNode* x3 = create_var_node();
+	VNode* x4 = create_var_node();
+	x1->val = -1.23;
+	x2->val = 7.1231;
+	x3->val = 2;
+	x4->val = -10;
+	list.push_back(x1);
+	list.push_back(x2);
+	list.push_back(x3);
+	list.push_back(x4);
+
+	OPNode* op1 = create_binary_op_node(OP_TIMES,x2,x1);
+	OPNode* op2 = create_uary_op_node(OP_SIN,x1);
+	OPNode* op3 = create_binary_op_node(OP_TIMES,op1,op2);
+	OPNode* op4 = create_binary_op_node(OP_DIVID,op3,x3);
+	OPNode* op5 = create_binary_op_node(OP_TIMES,x2,x4);
+	OPNode* op6 = create_binary_op_node(OP_PLUS,op4,op5);
+	OPNode* op7 = create_binary_op_node(OP_DIVID,x1,x2);
+	OPNode* op8 = create_binary_op_node(OP_MINUS,op6,op7);
+	return op8;
+}
+
+Node* build_nl_function1(vector<Node*>& list)
+{
+    // (x1*x2 * sin(x1))/x3 + x2*x4 - x1/x2
+    using namespace autodiff_placeholders;
+    return to_auto_diff_node(
+        (1_p * 2_p * sin_(1_p)) / 3_p + 2_p * 4_p - 1_p / 2_p,
+        list,
+	-1.23,
+	7.1231,
+	2,
+	-10
+    );
+}
+
+BOOST_AUTO_TEST_CASE( test_linear_fun1 )
+{
+	BOOST_TEST_MESSAGE("test_linear_fun1");
+	vector<Node*> list;
+	Node* root = build_linear_fun1(list);
+	vector<double> grad;
+	double val1 = grad_reverse(root,list,grad);
+	double val2 = eval_function(root);
+	double x1g[] = {-5.5440211108893697744548489936278,10.0,-0.16666666666666666666666666666667};
+
+	for(unsigned int i=0;i<3;i++){
+		CHECK_CLOSE(grad[i],x1g[i]);
+	}
+
+	double eval = 30.394751221800913;
+
+	CHECK_CLOSE(val1,eval);
+	CHECK_CLOSE(val2,eval);
+
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+}
+
+BOOST_AUTO_TEST_CASE( test_grad_sin )
+{
+	BOOST_TEST_MESSAGE("test_grad_sin");
+	VNode* x1 = create_var_node();
+	x1->val = 10;
+	OPNode* root = create_uary_op_node(OP_SIN,x1);
+	vector<Node*> nodes;
+	nodes.push_back(x1);
+	vector<double> grad;
+	grad_reverse(root,nodes,grad);
+	double x1g =  -0.83907152907645244;
+	//the matlab give cos(10) = -0.839071529076452
+
+	CHECK_CLOSE(grad[0],x1g);
+	BOOST_CHECK_EQUAL(nodes.size(),1);
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,1);
+}
+
+BOOST_AUTO_TEST_CASE(test_grad_single_node)
+{
+	VNode* x1 = create_var_node();
+	x1->val = -2;
+	vector<Node*> nodes;
+	nodes.push_back(x1);
+	vector<double> grad;
+	double val = grad_reverse(x1,nodes,grad);
+	CHECK_CLOSE(grad[0],1);
+	CHECK_CLOSE(val,-2);
+
+	EdgeSet s;
+	unsigned int n = 0;
+	nonlinearEdges(x1,s);
+	n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+
+	grad.clear();
+	nodes.clear();
+	PNode* p = create_param_node(-10);
+	//OPNode*	op = create_binary_op_node(TIMES,p,create_param_node(2));
+	val = grad_reverse(p,nodes,grad);
+	BOOST_CHECK_EQUAL(grad.size(),0);
+	CHECK_CLOSE(val,-10);
+
+	s.clear();
+	nonlinearEdges(p,s);
+	n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+}
+
+BOOST_AUTO_TEST_CASE(test_grad_neg)
+{
+	VNode* x1 = create_var_node();
+	x1->val = 10;
+	PNode* p2 = create_param_node(-1);
+	vector<Node*> nodes;
+	vector<double> grad;
+	nodes.push_back(x1);
+	Node* root = create_binary_op_node(OP_TIMES,x1,p2);
+	grad_reverse(root,nodes,grad);
+	CHECK_CLOSE(grad[0],-1);
+	BOOST_CHECK_EQUAL(nodes.size(),1);
+	nodes.clear();
+	grad.clear();
+	nodes.push_back(x1);
+	root = create_uary_op_node(OP_NEG,x1);
+	grad_reverse(root,nodes,grad);
+	CHECK_CLOSE(grad[0],-1);
+
+	EdgeSet s;
+	unsigned int n = 0;
+	nonlinearEdges(root,s);
+	n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+}
+
+BOOST_AUTO_TEST_CASE( test_nl_function)
+{
+	vector<Node*> list;
+	Node* root = build_nl_function1(list);
+	double val = eval_function(root);
+	vector<double> grad;
+	grad_reverse(root,list,grad);
+	double eval =-66.929555552886214;
+	double gx[] = {-4.961306690356109,-9.444611307649055,-2.064383410399700,7.123100000000000};
+	CHECK_CLOSE(val,eval);
+
+	for(unsigned int i=0;i<4;i++)
+	{
+		CHECK_CLOSE(grad[i],gx[i]);
+	}
+	unsigned int nzgrad = nzGrad(root);
+	unsigned int tol = numTotalNodes(root);
+	BOOST_CHECK_EQUAL(nzgrad,4);
+	BOOST_CHECK_EQUAL(tol,16);
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,11);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_1)
+{
+	vector<Node*> nodes;
+	Node* root = build_linear_fun1(nodes);
+	vector<double> grad;
+	double val = grad_reverse(root,nodes,grad);
+	double eval = eval_function(root);
+//	cout<<eval<<"\t"<<grad[0]<<"\t"<<grad[1]<<"\t"<<grad[2]<<"\t"<<endl;
+
+	CHECK_CLOSE(val,eval);
+
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+
+	static_cast<VNode*>(nodes[0])->u = 1;
+	double hval = 0;
+	vector<double> dhess;
+	hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],0);
+	}
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_2)
+{
+	vector<Node*> nodes;
+	Node* root = build_linear_function2(nodes);
+	vector<double> grad;
+	double val = grad_reverse(root,nodes,grad);
+	double eval = eval_function(root);
+
+	CHECK_CLOSE(val,eval);
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+
+	static_cast<VNode*>(nodes[0])->u = 1;
+	double hval = 0;
+	vector<double> dhess;
+	hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],0);
+	}
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_4)
+{
+	vector<Node*> nodes;
+//	Node* root = build_nl_function1(nodes);
+
+	VNode* x1 = create_var_node();
+	nodes.push_back(x1);
+	x1->val = 1;
+	x1->u =1;
+	Node* op = create_uary_op_node(OP_SIN,x1);
+	Node* root = create_uary_op_node(OP_SIN,op);
+	vector<double> grad;
+	double eval = eval_function(root);
+	vector<double> dhess;
+	double hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+	BOOST_CHECK_EQUAL(dhess.size(),1);
+	CHECK_CLOSE(dhess[0], -0.778395788418109);
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,1);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_3)
+{
+	vector<Node*> nodes;
+	VNode* x1 = create_var_node();
+	VNode* x2 = create_var_node();
+	nodes.push_back(x1);
+	nodes.push_back(x2);
+	x1->val = 2.5;
+	x2->val = -9;
+	Node* op1 = create_binary_op_node(OP_TIMES,x1,x2);
+	Node* root = create_binary_op_node(OP_TIMES,x1,op1);
+	double eval = eval_function(root);
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[0])->u = 1;
+
+	vector<double> dhess;
+	double hval = hess_reverse(root,nodes,dhess);
+	BOOST_CHECK_EQUAL(dhess.size(),2);
+	CHECK_CLOSE(hval,eval);
+	double hx[]={-18,5};
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		//Print("\t["<<i<<"]="<<dhess[i]);
+		CHECK_CLOSE(dhess[i],hx[i]);
+	}
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,3);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_5)
+{
+	vector<Node*> nodes;
+	VNode* x1 = create_var_node();
+	VNode* x2 = create_var_node();
+	nodes.push_back(x1);
+	nodes.push_back(x2);
+	x1->val = 2.5;
+	x2->val = -9;
+	Node* op1 = create_binary_op_node(OP_TIMES,x1,x1);
+	Node* op2 = create_binary_op_node(OP_TIMES,x2,x2);
+	Node* op3 = create_binary_op_node(OP_MINUS,op1,op2);
+	Node* op4 = create_binary_op_node(OP_PLUS,op1,op2);
+	Node* root = create_binary_op_node(OP_TIMES,op3,op4);
+
+	double eval = eval_function(root);
+
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[0])->u = 1;
+
+	vector<double> dhess;
+	double hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+	double hx[] ={75,0};
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],hx[i]);
+	}
+
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[1])->u = 1;
+
+	double hx2[] = {0, -972};
+	hval = hess_reverse(root,nodes,dhess);
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],hx2[i]);
+	}
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,4);
+}
+BOOST_AUTO_TEST_CASE( test_hess_reverse_6)
+{
+	vector<Node*> nodes;
+//	Node* root = build_nl_function1(nodes);
+
+	VNode* x1 = create_var_node();
+	VNode* x2 = create_var_node();
+	nodes.push_back(x1);
+	nodes.push_back(x2);
+	x1->val = 2.5;
+	x2->val = -9;
+	Node* root = create_binary_op_node(OP_POW,x1,x2);
+
+	double eval = eval_function(root);
+
+	static_cast<VNode*>(nodes[0])->u=1;static_cast<VNode*>(nodes[1])->u=0;
+	vector<double> dhess;
+	double hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+	double hx1[] ={0.003774873600000 , -0.000759862823419};
+	double hx2[] ={-0.000759862823419, 0.000220093141567};
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],hx1[i]);
+	}
+	static_cast<VNode*>(nodes[0])->u=0;static_cast<VNode*>(nodes[1])->u=1;
+	hess_reverse(root,nodes,dhess);
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],hx2[i]);
+	}
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,4);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_7)
+{
+	vector<Node*> nodes;
+	Node* root = build_nl_function1(nodes);
+
+	double eval = eval_function(root);
+
+
+	vector<double> dhess;
+	double hx0[] ={-1.747958066718855,
+			  -0.657091724418110,
+			   2.410459188139686,
+			                   0};
+	double hx1[] ={ -0.657091724418110,
+			   0.006806564792590,
+			  -0.289815306593997,
+			   1.000000000000000};
+	double hx2[] ={  2.410459188139686,
+			  -0.289815306593997,
+			   2.064383410399700,
+			                   0};
+	double hx3[] ={0,1,0,0};
+	for(unsigned int i=0;i<nodes.size();i++)
+	{
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[0])->u = 1;
+	double hval = hess_reverse(root,nodes,dhess);
+	CHECK_CLOSE(hval,eval);
+	for(unsigned int i=0;i<dhess.size();i++)
+	{
+		CHECK_CLOSE(dhess[i],hx0[i]);
+	}
+
+	for (unsigned int i = 0; i < nodes.size(); i++) {
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[1])->u = 1;
+	hess_reverse(root, nodes, dhess);
+	for (unsigned int i = 0; i < dhess.size(); i++) {
+		CHECK_CLOSE(dhess[i], hx1[i]);
+	}
+
+	for (unsigned int i = 0; i < nodes.size(); i++) {
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[2])->u = 1;
+	hess_reverse(root, nodes, dhess);
+	for (unsigned int i = 0; i < dhess.size(); i++) {
+		CHECK_CLOSE(dhess[i], hx2[i]);
+	}
+
+	for (unsigned int i = 0; i < nodes.size(); i++) {
+		static_cast<VNode*>(nodes[i])->u = 0;
+	}
+	static_cast<VNode*>(nodes[3])->u = 1;
+	hess_reverse(root, nodes, dhess);
+	for (unsigned i = 0; i < dhess.size(); i++) {
+		CHECK_CLOSE(dhess[i], hx3[i]);
+	}
+}
+
+#if FORWARD_ENABLED
+void test_hess_forward(Node* root, unsigned int& nvar)
+{
+	AutoDiff::num_var = nvar;
+	unsigned int len = (nvar+3)*nvar/2;
+	double* hess = new double[len];
+	hess_forward(root,nvar,&hess);
+	for(unsigned int i=0;i<len;i++){
+		cout<<"hess["<<i<<"]="<<hess[i]<<endl;
+	}
+	delete[] hess;
+}
+#endif
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse_8)
+{
+	vector<Node*> list;
+	vector<double> dhess;
+
+	VNode* x1 = create_var_node();
+	list.push_back(x1);
+	static_cast<VNode*>(list[0])->val = -10.5;
+	static_cast<VNode*>(list[0])->u = 1;
+	double deval = hess_reverse(x1,list,dhess);
+	CHECK_CLOSE(deval,-10.5);
+	BOOST_CHECK_EQUAL(dhess.size(),1);
+	BOOST_CHECK(isnan(dhess[0]));
+
+	EdgeSet s;
+	nonlinearEdges(x1,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+
+	PNode* p1 = create_param_node(-1.5);
+	list.clear();
+	deval = hess_reverse(p1,list,dhess);
+	CHECK_CLOSE(deval,-1.5);
+	BOOST_CHECK_EQUAL(dhess.size(),0);
+
+	s.clear();
+	nonlinearEdges(p1,s);
+	n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,0);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_revers9)
+{
+	vector<Node*> list;
+	vector<double> dhess;
+	VNode* x1 = create_var_node();
+	list.push_back(x1);
+	static_cast<VNode*>(list[0])->val = 2.5;
+	static_cast<VNode*>(list[0])->u =1;
+	Node* op1 = create_binary_op_node(OP_TIMES,x1,x1);
+	Node* root = create_binary_op_node(OP_TIMES,op1,op1);
+	double deval = hess_reverse(root,list,dhess);
+	double eval = eval_function(root);
+	CHECK_CLOSE(eval,deval);
+	BOOST_CHECK_EQUAL(dhess.size(),1);
+	CHECK_CLOSE(dhess[0],75);
+
+	EdgeSet s;
+	nonlinearEdges(root,s);
+	unsigned int n = nzHess(s);
+	BOOST_CHECK_EQUAL(n,1);
+
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_revers10)
+{
+	vector<Node*> list;
+	vector<double> dhess;
+	VNode* x1 = create_var_node();
+	VNode* x2 = create_var_node();
+	list.push_back(x1);
+	list.push_back(x2);
+	Node* op1 = create_binary_op_node(OP_TIMES, x1,x2);
+	Node* op2 = create_uary_op_node(OP_SIN,op1);
+	Node* op3 = create_uary_op_node(OP_COS,op1);
+	Node* root = create_binary_op_node(OP_TIMES, op2, op3);
+	static_cast<VNode*>(list[0])->val = 2.1;
+	static_cast<VNode*>(list[1])->val = 1.8;
+	double eval = eval_function(root);
+
+	//second column
+	static_cast<VNode*>(list[0])->u = 0;
+	static_cast<VNode*>(list[1])->u = 1;
+	double deval = hess_reverse(root,list,dhess);
+	CHECK_CLOSE(eval,deval);
+	BOOST_CHECK_EQUAL(dhess.size(),2);
+	CHECK_CLOSE(dhess[0], -6.945893481707861);
+	CHECK_CLOSE(dhess[1],  -8.441601940854081);
+
+	//first column
+	static_cast<VNode*>(list[0])->u = 1;
+	static_cast<VNode*>(list[1])->u = 0;
+	deval = hess_reverse(root,list,dhess);
+	CHECK_CLOSE(eval,deval);
+	BOOST_CHECK_EQUAL(dhess.size(),2);
+	CHECK_CLOSE(dhess[0], -6.201993262668304);
+	CHECK_CLOSE(dhess[1], -6.945893481707861);
+}
+
+BOOST_AUTO_TEST_CASE( test_grad_reverse11)
+{
+	vector<Node*> list;
+	VNode* x1 = create_var_node();
+	Node* p2 = create_param_node(2);
+	list.push_back(x1);
+	Node* op1 = create_binary_op_node(OP_POW,x1,p2);
+	static_cast<VNode*>(x1)->val = 0;
+	vector<double> grad;
+	grad_reverse(op1,list,grad);
+	BOOST_CHECK_EQUAL(grad.size(),1);
+	CHECK_CLOSE(grad[0],0);
+}
+
+BOOST_AUTO_TEST_CASE( test_hess_reverse12)
+{
+	vector<Node*> list;
+	VNode* x1 = create_var_node();
+	Node* p2 = create_param_node(2);
+	list.push_back(x1);
+	Node* op1 = create_binary_op_node(OP_POW,x1,p2);
+	x1->val = 0;
+	x1->u = 1;
+	vector<double> hess;
+	hess_reverse(op1,list,hess);
+	BOOST_CHECK_EQUAL(hess.size(),1);
+	CHECK_CLOSE(hess[0],2);
+}
+
+BOOST_AUTO_TEST_CASE( test_grad_reverse13)
+{
+	vector<Node*> list;
+	VNode* x1 = create_var_node();
+	PNode* p1 = create_param_node(0.090901);
+	VNode* x2 = create_var_node();
+	PNode* p2 = create_param_node(0.090901);
+	list.push_back(x1);
+	list.push_back(x2);
+	Node* op1 = create_binary_op_node(OP_TIMES,x1,p1);
+	Node* op2 = create_binary_op_node(OP_TIMES,x2,p2);
+	Node* root = create_binary_op_node(OP_PLUS,op1,op2);
+	x1->val = 1;
+	x2->val = 1;
+	vector<double> grad;
+	grad_reverse(root,list,grad);
+	BOOST_CHECK_EQUAL(grad.size(),2);
+	CHECK_CLOSE(grad[0],0.090901);
+	CHECK_CLOSE(grad[1],0.090901);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/boost/libs/yap/example/autodiff_library/ActNode.cpp b/src/boost/libs/yap/example/autodiff_library/ActNode.cpp
new file mode 100644
index 00000000..c21594f8
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/ActNode.cpp
@@ -0,0 +1,34 @@
+/*
+ * ActNode.cpp
+ *
+ *  Created on: 13 Apr 2013
+ *      Author: s0965328
+ */
+
+#include "ActNode.h"
+
+namespace AutoDiff {
+
+ActNode::ActNode() : AutoDiff::Node(),adj(NaN_Double){
+
+}
+
+ActNode::~ActNode() {
+}
+
+
+void ActNode::update_adj(double& v)
+{
+	assert(!isnan(adj));
+	assert(!isnan(v));
+	adj+=v;
+}
+
+void ActNode::grad_reverse_1_init_adj()
+{
+	adj = 1;
+}
+
+}
+
+
diff --git a/src/boost/libs/yap/example/autodiff_library/ActNode.h b/src/boost/libs/yap/example/autodiff_library/ActNode.h
new file mode 100644
index 00000000..58e77cc3
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/ActNode.h
@@ -0,0 +1,29 @@
+/*
+ * ActNode.h
+ *
+ *  Created on: 13 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef ACTNODE_H_
+#define ACTNODE_H_
+
+#include "Node.h"
+
+
+namespace AutoDiff {
+
+class ActNode : public Node{
+public:
+	ActNode();
+	virtual ~ActNode();
+
+	void update_adj(double& v);
+	void grad_reverse_1_init_adj();
+
+	double adj;
+};
+
+} // end namespace foo
+
+#endif /* ACTNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.cpp b/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.cpp
new file mode 100644
index 00000000..992d692d
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.cpp
@@ -0,0 +1,651 @@
+/*
+ * BinaryOPNode.cpp
+ *
+ *  Created on: 6 Nov 2013
+ *      Author: s0965328
+ */
+
+#include "auto_diff_types.h"
+#include "BinaryOPNode.h"
+#include "PNode.h"
+#include "Stack.h"
+#include "Tape.h"
+#include "EdgeSet.h"
+#include "Node.h"
+#include "VNode.h"
+#include "OPNode.h"
+#include "ActNode.h"
+#include "EdgeSet.h"
+
+namespace AutoDiff {
+
+BinaryOPNode::BinaryOPNode(OPCODE op_, Node* left_, Node* right_):OPNode(op_,left_),right(right_)
+{
+}
+
+OPNode* BinaryOPNode::createBinaryOpNode(OPCODE op, Node* left, Node* right)
+{
+	assert(left!=NULL && right!=NULL);
+	OPNode* node = NULL;
+	node = new BinaryOPNode(op,left,right);
+	return node;
+}
+
+BinaryOPNode::~BinaryOPNode() {
+	if(right->getType()!=VNode_Type)
+	{
+		delete right;
+		right = NULL;
+	}
+}
+
+void BinaryOPNode::inorder_visit(int level,ostream& oss){
+	if(left!=NULL){
+		left->inorder_visit(level+1,oss);
+	}
+	oss<<this->toString(level)<<endl;
+	if(right!=NULL){
+		right->inorder_visit(level+1,oss);
+	}
+}
+
+void BinaryOPNode::collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total){
+	total++;
+	if (left != NULL) {
+		left->collect_vnodes(nodes,total);
+	}
+	if (right != NULL) {
+		right->collect_vnodes(nodes,total);
+	}
+
+}
+
+void BinaryOPNode::eval_function()
+{
+	assert(left!=NULL && right!=NULL);
+	left->eval_function();
+	right->eval_function();
+	this->calc_eval_function();
+}
+
+void BinaryOPNode::calc_eval_function()
+{
+	double x = NaN_Double;
+	double rx = SV->pop_back();
+	double lx = SV->pop_back();
+	switch (op)
+	{
+	case OP_PLUS:
+		x = lx + rx;
+		break;
+	case OP_MINUS:
+		x = lx - rx;
+		break;
+	case OP_TIMES:
+		x = lx * rx;
+		break;
+	case OP_DIVID:
+		x = lx / rx;
+		break;
+	case OP_POW:
+		x = pow(lx,rx);
+		break;
+	default:
+		cerr<<"op["<<op<<"] not yet implemented!!"<<endl;
+		assert(false);
+		break;
+	}
+	SV->push_back(x);
+}
+
+
+//1. visiting left if not NULL
+//2. then, visiting right if not NULL
+//3. calculating the immediate derivative hu and hv
+void BinaryOPNode::grad_reverse_0()
+{
+	assert(left!=NULL && right != NULL);
+	this->adj = 0;
+	left->grad_reverse_0();
+	right->grad_reverse_0();
+	this->calc_grad_reverse_0();
+}
+
+//right left - right most traversal
+void BinaryOPNode::grad_reverse_1()
+{
+	assert(right!=NULL && left!=NULL);
+	double r_adj = SD->pop_back()*this->adj;
+	right->update_adj(r_adj);
+	double l_adj = SD->pop_back()*this->adj;
+	left->update_adj(l_adj);
+
+	right->grad_reverse_1();
+	left->grad_reverse_1();
+}
+
+void BinaryOPNode::calc_grad_reverse_0()
+{
+	assert(left!=NULL && right != NULL);
+	double l_dh = NaN_Double;
+	double r_dh = NaN_Double;
+	double rx = SV->pop_back();
+	double lx = SV->pop_back();
+	double x = NaN_Double;
+	switch (op)
+	{
+	case OP_PLUS:
+		x = lx + rx;
+		l_dh = 1;
+		r_dh = 1;
+		break;
+	case OP_MINUS:
+		x = lx - rx;
+		l_dh = 1;
+		r_dh = -1;
+		break;
+	case OP_TIMES:
+		x = lx * rx;
+		l_dh = rx;
+		r_dh = lx;
+		break;
+	case OP_DIVID:
+		x = lx / rx;
+		l_dh = 1 / rx;
+		r_dh = -(lx) / pow(rx, 2);
+		break;
+	case OP_POW:
+		if(right->getType()==PNode_Type){
+			x = pow(lx,rx);
+			l_dh = rx*pow(lx,(rx-1));
+			r_dh = 0;
+		}
+		else{
+			assert(lx>0.0); //otherwise log(lx) is not defined in read number
+			x = pow(lx,rx);
+			l_dh = rx*pow(lx,(rx-1));
+			r_dh = pow(lx,rx)*log(lx);  //this is for x1^x2 when x1=0 cause r_dh become +inf, however d(0^x2)/d(x2) = 0
+		}
+		break;
+	default:
+		cerr<<"error op not impl"<<endl;
+		break;
+	}
+	SV->push_back(x);
+	SD->push_back(l_dh);
+	SD->push_back(r_dh);
+}
+
+void BinaryOPNode::hess_reverse_0_init_n_in_arcs()
+{
+	this->left->hess_reverse_0_init_n_in_arcs();
+	this->right->hess_reverse_0_init_n_in_arcs();
+	this->Node::hess_reverse_0_init_n_in_arcs();
+}
+
+void BinaryOPNode::hess_reverse_1_clear_index()
+{
+	this->left->hess_reverse_1_clear_index();
+	this->right->hess_reverse_1_clear_index();
+	this->Node::hess_reverse_1_clear_index();
+}
+
+unsigned int BinaryOPNode::hess_reverse_0()
+{
+	assert(this->left!=NULL && right!=NULL);
+	if(index==0)
+	{
+		unsigned int lindex=0, rindex=0;
+		lindex = left->hess_reverse_0();
+		rindex = right->hess_reverse_0();
+		assert(lindex!=0 && rindex !=0);
+		II->set(lindex);
+		II->set(rindex);
+		double rx,rx_bar,rw,rw_bar;
+		double lx,lx_bar,lw,lw_bar;
+		double x,x_bar,w,w_bar;
+		double r_dh, l_dh;
+		right->hess_reverse_0_get_values(rindex,rx,rx_bar,rw,rw_bar);
+		left->hess_reverse_0_get_values(lindex,lx,lx_bar,lw,lw_bar);
+		switch(op)
+		{
+		case OP_PLUS:
+	//		cout<<"lindex="<<lindex<<"\trindex="<<rindex<<"\tI="<<I<<endl;
+			x = lx + rx;
+	//		cout<<lx<<"\t+"<<rx<<"\t="<<x<<"\t\t"<<toString(0)<<endl;
+			x_bar = 0;
+			l_dh = 1;
+			r_dh = 1;
+			w = lw * l_dh  + rw * r_dh;
+	//		cout<<lw<<"\t+"<<rw<<"\t="<<w<<"\t\t"<<toString(0)<<endl;
+			w_bar = 0;
+			break;
+		case OP_MINUS:
+			x = lx - rx;
+			x_bar = 0;
+			l_dh = 1;
+			r_dh = -1;
+			w = lw * l_dh  + rw * r_dh;
+			w_bar = 0;
+			break;
+		case OP_TIMES:
+			x = lx * rx;
+			x_bar = 0;
+			l_dh = rx;
+			r_dh = lx;
+			w = lw * l_dh  + rw * r_dh;
+			w_bar = 0;
+			break;
+		case OP_DIVID:
+			x = lx / rx;
+			x_bar = 0;
+			l_dh = 1/rx;
+			r_dh = -lx/pow(rx,2);
+			w = lw * l_dh  + rw * r_dh;
+			w_bar = 0;
+			break;
+		case OP_POW:
+			if(right->getType()==PNode_Type)
+			{
+				x = pow(lx,rx);
+				x_bar = 0;
+				l_dh = rx*pow(lx,(rx-1));
+				r_dh = 0;
+				w = lw * l_dh + rw * r_dh;
+				w_bar = 0;
+			}
+			else
+			{
+				assert(lx>0.0); //otherwise log(lx) undefined in real number
+				x = pow(lx,rx);
+				x_bar = 0;
+				l_dh = rx*pow(lx,(rx-1));
+				r_dh = pow(lx,rx)*log(lx);   //log(lx) cause -inf when lx=0;
+				w = lw * l_dh  + rw * r_dh;
+				w_bar = 0;
+			}
+			break;
+		default:
+			cerr<<"op["<<op<<"] not yet implemented!"<<endl;
+			assert(false);
+			break;
+		}
+		TT->set(x);
+		TT->set(x_bar);
+		TT->set(w);
+		TT->set(w_bar);
+		TT->set(l_dh);
+		TT->set(r_dh);
+		assert(TT->index == TT->index);
+		index = TT->index;
+	}
+	return index;
+}
+
+void BinaryOPNode::hess_reverse_0_get_values(unsigned int i,double& x, double& x_bar, double& w, double& w_bar)
+{
+	--i; // skip the r_dh (ie, dh/du)
+	--i; // skip the l_dh (ie. dh/dv)
+	w_bar = TT->get(--i);
+	w = TT->get(--i);
+	x_bar = TT->get(--i);
+	x = TT->get(--i);
+}
+
+void BinaryOPNode::hess_reverse_1(unsigned int i)
+{
+	n_in_arcs--;
+	if(n_in_arcs==0)
+	{
+		assert(right!=NULL && left!=NULL);
+		unsigned int rindex = II->get(--(II->index));
+		unsigned int lindex = II->get(--(II->index));
+	//	cout<<"ri["<<rindex<<"]\tli["<<lindex<<"]\t"<<this->toString(0)<<endl;
+		double r_dh = TT->get(--i);
+		double l_dh = TT->get(--i);
+		double w_bar = TT->get(--i);
+		--i; //skip w
+		double x_bar = TT->get(--i);
+		--i; //skip x
+
+		double lw_bar=0,rw_bar=0;
+		double lw=0,lx=0; left->hess_reverse_1_get_xw(lindex,lw,lx);
+		double rw=0,rx=0; right->hess_reverse_1_get_xw(rindex,rw,rx);
+		switch(op)
+		{
+		case OP_PLUS:
+			assert(l_dh==1);
+			assert(r_dh==1);
+			lw_bar += w_bar*l_dh;
+			rw_bar += w_bar*r_dh;
+			break;
+		case OP_MINUS:
+			assert(l_dh==1);
+			assert(r_dh==-1);
+			lw_bar += w_bar*l_dh;
+			rw_bar += w_bar*r_dh;
+			break;
+		case OP_TIMES:
+			assert(rx == l_dh);
+			assert(lx == r_dh);
+			lw_bar += w_bar*rx;
+			lw_bar += x_bar*lw*0 + x_bar*rw*1;
+			rw_bar += w_bar*lx;
+			rw_bar += x_bar*lw*1 + x_bar*rw*0;
+			break;
+		case OP_DIVID:
+			lw_bar += w_bar*l_dh;
+			lw_bar += x_bar*lw*0 + x_bar*rw*-1/(pow(rx,2));
+			rw_bar += w_bar*r_dh;
+			rw_bar += x_bar*lw*-1/pow(rx,2) + x_bar*rw*2*lx/pow(rx,3);
+			break;
+		case OP_POW:
+			if(right->getType()==PNode_Type){
+				lw_bar += w_bar*l_dh;
+				lw_bar += x_bar*lw*pow(lx,rx-2)*rx*(rx-1) + 0;
+				rw_bar += w_bar*r_dh; assert(r_dh==0.0);
+				rw_bar += 0;
+			}
+			else{
+				assert(lx>0.0); //otherwise log(lx) is not define in Real
+				lw_bar += w_bar*l_dh;
+				lw_bar += x_bar*lw*pow(lx,rx-2)*rx*(rx-1) + x_bar*rw*pow(lx,rx-1)*(rx*log(lx)+1);  //cause log(lx)=-inf when
+				rw_bar += w_bar*r_dh;
+				rw_bar += x_bar*lw*pow(lx,rx-1)*(rx*log(lx)+1) + x_bar*rw*pow(lx,rx)*pow(log(lx),2);
+			}
+			break;
+		default:
+			cerr<<"op["<<op<<"] not yet implemented !"<<endl;
+			assert(false);
+			break;
+		}
+		double rx_bar = x_bar*r_dh;
+		double lx_bar = x_bar*l_dh;
+		right->update_x_bar(rindex,rx_bar);
+		left->update_x_bar(lindex,lx_bar);
+		right->update_w_bar(rindex,rw_bar);
+		left->update_w_bar(lindex,lw_bar);
+
+
+		this->right->hess_reverse_1(rindex);
+		this->left->hess_reverse_1(lindex);
+	}
+}
+void BinaryOPNode::hess_reverse_1_init_x_bar(unsigned int i)
+{
+	TT->at(i-5) = 1;
+}
+void BinaryOPNode::update_x_bar(unsigned int i ,double v)
+{
+	TT->at(i-5) += v;
+}
+void BinaryOPNode::update_w_bar(unsigned int i ,double v)
+{
+	TT->at(i-3) += v;
+}
+void BinaryOPNode::hess_reverse_1_get_xw(unsigned int i,double& w,double& x)
+{
+	w = TT->get(i-4);
+	x = TT->get(i-6);
+}
+void BinaryOPNode::hess_reverse_get_x(unsigned int i,double& x)
+{
+	x = TT->get(i-6);
+}
+
+
+void BinaryOPNode::nonlinearEdges(EdgeSet& edges)
+{
+	for(list<Edge>::iterator it=edges.edges.begin();it!=edges.edges.end();)
+	{
+		Edge e = *it;
+		if(e.a==this || e.b == this){
+			if(e.a == this && e.b == this)
+			{
+				Edge e1(left,left);
+				Edge e2(right,right);
+				Edge e3(left,right);
+				edges.insertEdge(e1);
+				edges.insertEdge(e2);
+				edges.insertEdge(e3);
+			}
+			else
+			{
+				Node* o = e.a==this? e.b: e.a;
+				Edge e1(left,o);
+				Edge e2(right,o);
+				edges.insertEdge(e1);
+				edges.insertEdge(e2);
+			}
+			it = edges.edges.erase(it);
+		}
+		else
+		{
+			it++;
+		}
+	}
+
+	Edge e1(left,right);
+	Edge e2(left,left);
+	Edge e3(right,right);
+	switch(op)
+	{
+	case OP_PLUS:
+	case OP_MINUS:
+		//do nothing for linear operator
+		break;
+	case OP_TIMES:
+		edges.insertEdge(e1);
+		break;
+	case OP_DIVID:
+		edges.insertEdge(e1);
+		edges.insertEdge(e3);
+		break;
+	case OP_POW:
+		edges.insertEdge(e1);
+		edges.insertEdge(e2);
+		edges.insertEdge(e3);
+		break;
+	default:
+		cerr<<"op["<<op<<"] not yet implmented !"<<endl;
+		assert(false);
+		break;
+	}
+	left->nonlinearEdges(edges);
+	right->nonlinearEdges(edges);
+}
+
+#if FORWARD_ENABLED
+
+void BinaryOPNode::hess_forward(unsigned int len, double** ret_vec)
+{
+	double* lvec = NULL;
+	double* rvec = NULL;
+	if(left!=NULL){
+		left->hess_forward(len,&lvec);
+	}
+	if(right!=NULL){
+		right->hess_forward(len,&rvec);
+	}
+
+	*ret_vec = new double[len];
+	hess_forward_calc0(len,lvec,rvec,*ret_vec);
+	//delete lvec, rvec
+	delete[] lvec;
+	delete[] rvec;
+}
+
+void BinaryOPNode::hess_forward_calc0(unsigned int& len, double* lvec, double* rvec, double* ret_vec)
+{
+	double hu = NaN_Double, hv= NaN_Double;
+	double lval = NaN_Double, rval = NaN_Double;
+	double val = NaN_Double;
+	unsigned int index = 0;
+	switch (op)
+	{
+	case OP_PLUS:
+		rval = SV->pop_back();
+		lval = SV->pop_back();
+		val = lval + rval;
+		SV->push_back(val);
+		//calculate the first order derivatives
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			ret_vec[i] = lvec[i]+rvec[i];
+		}
+		//calculate the second order
+		index = AutoDiff::num_var;
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			for(unsigned int j=i;j<AutoDiff::num_var;++j){
+				ret_vec[index] = lvec[index] + 0 + rvec[index] + 0;
+				++index;
+			}
+		}
+		assert(index==len);
+		break;
+	case OP_MINUS:
+		rval = SV->pop_back();
+		lval = SV->pop_back();
+		val = lval + rval;
+		SV->push_back(val);
+		//calculate the first order derivatives
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			ret_vec[i] = lvec[i] - rvec[i];
+		}
+		//calculate the second order
+		index = AutoDiff::num_var;
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			for(unsigned int j=i;j<AutoDiff::num_var;++j){
+				ret_vec[index] = lvec[index] + 0 - rvec[index] + 0;
+				++index;
+			}
+		}
+		assert(index==len);
+		break;
+	case OP_TIMES:
+		rval = SV->pop_back();
+		lval = SV->pop_back();
+		val = lval * rval;
+		SV->push_back(val);
+		hu = rval;
+		hv = lval;
+		//calculate the first order derivatives
+		for(unsigned int i =0;i<AutoDiff::num_var;++i)
+		{
+			ret_vec[i] = hu*lvec[i] + hv*rvec[i];
+		}
+		//calculate the second order
+		index = AutoDiff::num_var;
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			for(unsigned int j=i;j<AutoDiff::num_var;++j)
+			{
+				ret_vec[index] = hu * lvec[index] + lvec[i] * rvec[j]+hv * rvec[index] + rvec[i] * lvec[j];
+				++index;
+			}
+		}
+		assert(index==len);
+		break;
+	case OP_POW:
+		rval = SV->pop_back();
+		lval = SV->pop_back();
+		val = pow(lval,rval);
+		SV->push_back(val);
+		if(left->getType()==PNode_Type && right->getType()==PNode_Type)
+		{
+			std::fill_n(ret_vec,len,0);
+		}
+		else
+		{
+			hu = rval*pow(lval,(rval-1));
+			hv = pow(lval,rval)*log(lval);
+			if(left->getType()==PNode_Type)
+			{
+				double coeff = pow(log(lval),2)*pow(lval,rval);
+				//calculate the first order derivatives
+				for(unsigned int i =0;i<AutoDiff::num_var;++i)
+				{
+					ret_vec[i] = hu*lvec[i] + hv*rvec[i];
+				}
+				//calculate the second order
+				index = AutoDiff::num_var;
+				for(unsigned int i=0;i<AutoDiff::num_var;++i)
+				{
+					for(unsigned int j=i;j<AutoDiff::num_var;++j)
+					{
+						ret_vec[index] = 0 + 0 + hv * rvec[index] + rvec[i] * coeff * rvec[j];
+						++index;
+					}
+				}
+			}
+			else if(right->getType()==PNode_Type)
+			{
+				double coeff = rval*(rval-1)*pow(lval,rval-2);
+				//calculate the first order derivatives
+				for(unsigned int i =0;i<AutoDiff::num_var;++i)
+				{
+					ret_vec[i] = hu*lvec[i] + hv*rvec[i];
+				}
+				//calculate the second order
+				index = AutoDiff::num_var;
+				for(unsigned int i=0;i<AutoDiff::num_var;++i)
+				{
+					for(unsigned int j=i;j<AutoDiff::num_var;++j)
+					{
+						ret_vec[index] = hu*lvec[index] + lvec[i] * coeff * lvec[j] + 0 + 0;
+						++index;
+					}
+				}
+			}
+			else
+			{
+				assert(false);
+			}
+		}
+		assert(index==len);
+		break;
+	case OP_SIN: //TODO should move to UnaryOPNode.cpp?
+		assert(left!=NULL&&right==NULL);
+		lval = SV->pop_back();
+		val = sin(lval);
+		SV->push_back(val);
+		hu = cos(lval);
+
+		double coeff;
+		coeff = -val; //=sin(left->val); -- and avoid cross initialisation
+		//calculate the first order derivatives
+		for(unsigned int i =0;i<AutoDiff::num_var;++i)
+		{
+			ret_vec[i] = hu*lvec[i] + 0;
+		}
+		//calculate the second order
+		index = AutoDiff::num_var;
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			for(unsigned int j=i;j<AutoDiff::num_var;++j)
+			{
+				ret_vec[index] = hu*lvec[index] + lvec[i] * coeff * lvec[j] + 0 + 0;
+				++index;
+			}
+		}
+		assert(index==len);
+		break;
+	default:
+		cerr<<"op["<<op<<"] not yet implemented!";
+		break;
+	}
+}
+#endif
+
+
+string BinaryOPNode::toString(int level){
+	ostringstream oss;
+	string s(level,'\t');
+	oss<<s<<"[BinaryOPNode]("<<op<<")";
+	return oss.str();
+}
+
+} /* namespace AutoDiff */
diff --git a/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.h b/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.h
new file mode 100644
index 00000000..7abc702a
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/BinaryOPNode.h
@@ -0,0 +1,57 @@
+/*
+ * BinaryOPNode.h
+ *
+ *  Created on: 6 Nov 2013
+ *      Author: s0965328
+ */
+
+#ifndef BINARYOPNODE_H_
+#define BINARYOPNODE_H_
+
+#include "OPNode.h"
+
+namespace AutoDiff {
+
+class EdgeSet;
+
+class BinaryOPNode: public OPNode {
+public:
+
+	static OPNode* createBinaryOpNode(OPCODE op, Node* left, Node* right);
+	virtual ~BinaryOPNode();
+
+	void collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total);
+	void eval_function();
+
+	void grad_reverse_0();
+	void grad_reverse_1();
+
+	void hess_forward(unsigned int len, double** ret_vec);
+
+	unsigned int hess_reverse_0();
+	void hess_reverse_0_init_n_in_arcs();
+	void hess_reverse_0_get_values(unsigned int,double&, double&, double&, double&);
+	void hess_reverse_1(unsigned int i);
+	void hess_reverse_1_init_x_bar(unsigned int);
+	void update_x_bar(unsigned int,double);
+	void update_w_bar(unsigned int,double);
+	void hess_reverse_1_get_xw(unsigned int, double&,double&);
+	void hess_reverse_get_x(unsigned int,double& x);
+	void hess_reverse_1_clear_index();
+
+	void nonlinearEdges(EdgeSet& a);
+
+	void inorder_visit(int level,ostream& oss);
+	string toString(int level);
+
+	Node* right;
+
+private:
+	BinaryOPNode(OPCODE op, Node* left, Node* right);
+	void calc_eval_function();
+	void calc_grad_reverse_0();
+	void hess_forward_calc0(unsigned int& len, double* lvec, double* rvec,double* ret_vec);
+};
+
+} /* namespace AutoDiff */
+#endif /* BINARYOPNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/Edge.cpp b/src/boost/libs/yap/example/autodiff_library/Edge.cpp
new file mode 100644
index 00000000..4a7183b6
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Edge.cpp
@@ -0,0 +1,54 @@
+/*
+ * Edge.cpp
+ *
+ *  Created on: 12 Nov 2013
+ *      Author: s0965328
+ */
+
+#include "Edge.h"
+#include <iostream>
+#include <sstream>
+
+namespace AutoDiff {
+
+Edge::Edge(Node* a_,Node* b_):a(a_),b(b_) {
+
+}
+
+Edge::~Edge() {
+	a = NULL;
+	b = NULL;
+}
+
+Edge::Edge(const Edge& e)
+{
+	a = e.a;
+	b = e.b;
+}
+
+bool Edge::isEqual(Edge* e)
+{
+	if(e->a == a && e->b == b)
+	{
+		return true;
+	}
+	else if(e->b == a && e->a == b)
+	{
+		return true;
+	}
+	return false;
+}
+
+bool Edge::isEqual(Edge& e)
+{
+	return isEqual(&e);
+}
+
+string Edge::toString()
+{
+	ostringstream oss;
+	oss<<""<<a->toString(0)<<"|"<<a<<" ----- "<<b->toString(0)<<"|"<<b<<""<<endl;
+	return oss.str();
+}
+
+} /* namespace AutoDiff */
diff --git a/src/boost/libs/yap/example/autodiff_library/Edge.h b/src/boost/libs/yap/example/autodiff_library/Edge.h
new file mode 100644
index 00000000..10126ac2
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Edge.h
@@ -0,0 +1,33 @@
+/*
+ * Edge.h
+ *
+ *  Created on: 12 Nov 2013
+ *      Author: s0965328
+ */
+
+#ifndef EDGE_H_
+#define EDGE_H_
+
+
+#include "Node.h"
+
+namespace AutoDiff {
+
+class Edge {
+public:
+	Edge(Node* a, Node* b);
+	Edge(const Edge& e);
+	virtual ~Edge();
+
+	bool isEqual(Edge*);
+	bool isEqual(Edge&);
+	std::string toString();
+
+	Node* a;
+	Node* b;
+
+
+};
+
+} /* namespace AutoDiff */
+#endif /* EDGE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/EdgeSet.cpp b/src/boost/libs/yap/example/autodiff_library/EdgeSet.cpp
new file mode 100644
index 00000000..20e16132
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/EdgeSet.cpp
@@ -0,0 +1,76 @@
+/*
+ * EdgeSet.cpp
+ *
+ *  Created on: 12 Nov 2013
+ *      Author: s0965328
+ */
+
+#include "EdgeSet.h"
+#include "Edge.h"
+#include <sstream>
+
+using namespace std;
+namespace AutoDiff {
+
+EdgeSet::EdgeSet() {
+	// TODO Auto-generated constructor stub
+
+}
+
+EdgeSet::~EdgeSet() {
+	edges.clear();
+}
+
+bool EdgeSet::containsEdge(Edge& e)
+{
+	list<Edge>::iterator it = edges.begin();
+	for(;it!= edges.end();it++){
+		Edge eit = *it;
+		if(eit.isEqual(e))
+		{
+			return true;
+		}
+	}
+	return false;
+}
+
+void EdgeSet::insertEdge(Edge& e) {
+	if(!containsEdge(e)){
+		edges.push_front(e);
+	}
+}
+
+void EdgeSet::clear() {
+	edges.clear();
+}
+
+unsigned int EdgeSet::size(){
+	return edges.size();
+}
+
+unsigned int EdgeSet::numSelfEdges(){
+	unsigned int diag = 0;
+	list<Edge>::iterator it = edges.begin();
+	for(;it!=edges.end();it++)
+	{
+		Edge eit = *it;
+		if(eit.a == eit.b)
+		{
+			diag++;
+		}
+	}
+	return diag;
+}
+
+string EdgeSet::toString()
+{
+	ostringstream oss;
+	list<Edge>::iterator it = edges.begin();
+	for(;it!=edges.end();it++)
+	{
+		oss<<(*it).toString()<<endl;
+	}
+	return oss.str();
+}
+
+} /* namespace AutoDiff */
diff --git a/src/boost/libs/yap/example/autodiff_library/EdgeSet.h b/src/boost/libs/yap/example/autodiff_library/EdgeSet.h
new file mode 100644
index 00000000..26b2be12
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/EdgeSet.h
@@ -0,0 +1,33 @@
+/*
+ * EdgeSet.h
+ *
+ *  Created on: 12 Nov 2013
+ *      Author: s0965328
+ */
+
+#ifndef EDGESET_H_
+#define EDGESET_H_
+
+#include "Edge.h"
+#include <list>
+
+namespace AutoDiff {
+
+class EdgeSet {
+public:
+	EdgeSet();
+	virtual ~EdgeSet();
+
+	void insertEdge(Edge& e);
+	bool containsEdge(Edge& e);
+	unsigned int numSelfEdges();
+	void clear();
+	unsigned int size();
+	std::string toString();
+
+
+	std::list<Edge> edges;
+};
+
+} /* namespace AutoDiff */
+#endif /* EDGESET_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/LICENSE b/src/boost/libs/yap/example/autodiff_library/LICENSE
new file mode 100644
index 00000000..f09534cf
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/LICENSE
@@ -0,0 +1,22 @@
+The MIT License (MIT)
+
+Copyright (c) 2014 fqiang
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
diff --git a/src/boost/libs/yap/example/autodiff_library/Node.cpp b/src/boost/libs/yap/example/autodiff_library/Node.cpp
new file mode 100644
index 00000000..13ed5764
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Node.cpp
@@ -0,0 +1,32 @@
+/*
+ * Node.cpp
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#include "Node.h"
+
+namespace AutoDiff {
+
+unsigned int Node::DEFAULT_INDEX = 0;
+Node::Node():index(Node::DEFAULT_INDEX),n_in_arcs(0){
+}
+
+
+Node::~Node() {
+}
+
+void Node::hess_reverse_0_init_n_in_arcs()
+{
+	n_in_arcs++;
+//	cout<<this->toString(0)<<endl;
+}
+
+void Node::hess_reverse_1_clear_index()
+{
+	index = Node::DEFAULT_INDEX;
+}
+
+}
+
diff --git a/src/boost/libs/yap/example/autodiff_library/Node.h b/src/boost/libs/yap/example/autodiff_library/Node.h
new file mode 100644
index 00000000..f89c2bb1
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Node.h
@@ -0,0 +1,65 @@
+/*
+ * Node.h
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef NODE_H_
+#define NODE_H_
+
+#include <boost/unordered_set.hpp>
+#include "auto_diff_types.h"
+
+using namespace std;
+
+namespace AutoDiff {
+
+class EdgeSet;
+
+class Node {
+public:
+	Node();
+	virtual ~Node();
+
+	virtual void eval_function() = 0;
+	virtual void grad_reverse_0() = 0;
+	virtual void grad_reverse_1_init_adj() = 0;
+	virtual void grad_reverse_1() = 0;
+	virtual void update_adj(double& v) = 0;
+	virtual unsigned int hess_reverse_0() = 0;
+	virtual void hess_reverse_0_init_n_in_arcs();
+	virtual void hess_reverse_0_get_values(unsigned int,double&, double&,double&, double&) = 0;
+	virtual void hess_reverse_1(unsigned int i) = 0;
+	virtual void hess_reverse_1_init_x_bar(unsigned int) = 0;
+	virtual void update_x_bar(unsigned int,double) = 0;
+	virtual void update_w_bar(unsigned int,double) = 0;
+	virtual void hess_reverse_1_get_xw(unsigned int, double&,double&) = 0;
+	virtual void hess_reverse_get_x(unsigned int,double& x)=0;
+	virtual void hess_reverse_1_clear_index();
+	//routing for checking non-zero structures
+	virtual void collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total) = 0;
+	virtual void nonlinearEdges(EdgeSet&) = 0;
+#if FORWARD_ENABLED
+	virtual void hess_forward(unsigned int len, double** ret_vec) = 0;
+#endif
+
+	//other utility methods
+	virtual void inorder_visit( int level,ostream& oss) = 0;
+	virtual string toString(int levl) = 0;
+	virtual TYPE getType() = 0;
+
+
+	//! index on the tape
+	unsigned int index;
+	//! number of incoming arcs
+	//! n_in_arcs in root node equals 1 before evaluation and 0 after evaluation
+	unsigned int n_in_arcs;
+
+	static unsigned int DEFAULT_INDEX;
+
+};
+
+} // end namespace foo
+
+#endif /* NODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/OPNode.cpp b/src/boost/libs/yap/example/autodiff_library/OPNode.cpp
new file mode 100644
index 00000000..0f647931
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/OPNode.cpp
@@ -0,0 +1,37 @@
+/*
+ * OpNode.cpp
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#include "OPNode.h"
+#include "Stack.h"
+#include "Tape.h"
+#include "PNode.h"
+/***********************************************************
+	     h
+	    / \
+	   u   v  ----- hu  hv represent dh/du dh/dv resepectively.
+	   - - -
+	  x1....xn
+***********************************************************/
+
+namespace AutoDiff{
+
+OPNode::OPNode(OPCODE op, Node* left) : ActNode(), op(op), left(left),val(NaN_Double) {
+}
+
+TYPE OPNode::getType()
+{
+	return OPNode_Type;
+}
+
+OPNode::~OPNode() {
+	if(left->getType()!=VNode_Type)
+	{
+		delete left;
+		this->left = NULL;
+	}
+}
+}
diff --git a/src/boost/libs/yap/example/autodiff_library/OPNode.h b/src/boost/libs/yap/example/autodiff_library/OPNode.h
new file mode 100644
index 00000000..e5ed2da9
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/OPNode.h
@@ -0,0 +1,37 @@
+/*
+ * OpNode.h
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef OPNODE_H_
+#define OPNODE_H_
+
+#include "Node.h"
+#include "ActNode.h"
+
+namespace AutoDiff {
+
+using namespace std;
+
+class OPNode: public ActNode {
+public:
+	OPNode(OPCODE op,Node* left);
+	virtual ~OPNode();
+
+	TYPE getType();
+
+	OPCODE op;
+	Node* left;
+	double val;
+
+
+
+private:
+
+};
+
+}
+
+#endif /* OPNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/PNode.cpp b/src/boost/libs/yap/example/autodiff_library/PNode.cpp
new file mode 100644
index 00000000..ee07a1f2
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/PNode.cpp
@@ -0,0 +1,147 @@
+/*
+ * PNode.cpp
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#include "PNode.h"
+#include "Stack.h"
+#include "Tape.h"
+#include "EdgeSet.h"
+
+namespace AutoDiff {
+
+PNode::PNode(double value):pval(value) {
+	assert(!isnan(value));
+}
+
+PNode::~PNode() {
+}
+
+void PNode::inorder_visit(int level,ostream& oss){
+	oss<<this->toString(level)<<endl;
+}
+
+void PNode::collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total)
+{
+	//do not fill this to nodes, as this is a parameter node
+	total++;
+}
+
+void PNode::eval_function()
+{
+	SV->push_back(pval);
+}
+
+string PNode::toString(int level)
+{
+	ostringstream oss;
+	string s(level,'\t');
+	oss<<s<<"[PNode]("<<pval<<")";
+	return oss.str();
+}
+
+void PNode::grad_reverse_0()
+{
+	SV->push_back(pval);
+}
+void PNode::grad_reverse_1_init_adj()
+{
+	//do nothing as PNode does not have adjoint
+}
+
+void PNode::grad_reverse_1()
+{
+	//do nothing
+	//this is a parameter
+}
+
+void PNode::update_adj(double& v)
+{
+	//do nothing
+	//no adj for PNode
+}
+
+unsigned int PNode::hess_reverse_0()
+{
+	if(index==0)
+	{
+		TT->set(pval);
+		assert(TT->index == TT->index);
+		index = TT->index;
+	}
+	return index;
+}
+
+void PNode::hess_reverse_0_get_values(unsigned int i,double& x,double& x_bar,double& w,double& w_bar)
+{
+	x = TT->get(--i);
+	x_bar = 0;
+	w = 0;
+	w_bar = 0;
+}
+
+void PNode::hess_reverse_1(unsigned int i)
+{
+	n_in_arcs--;
+	//leaf node do nothing
+}
+
+void PNode::hess_reverse_1_init_x_bar(unsigned int)
+{
+	//do nothing as Parameter does not have x_bar
+}
+
+void PNode::update_x_bar(unsigned int i ,double v)
+{
+	//do nothing as Parameter does not have x_bar
+}
+void PNode::update_w_bar(unsigned int i ,double v)
+{
+	//do nothing as Parameter does not have w_bar
+}
+void PNode::hess_reverse_1_get_xw(unsigned int i, double& w,double& x)
+{
+	//do nothing as Parameter does not have w
+	x = TT->get(i-1);
+	w = 0;
+}
+void PNode::hess_reverse_get_x(unsigned int i, double& x)
+{
+	x = TT->get(i-1);
+}
+
+void PNode::nonlinearEdges(EdgeSet& edges)
+{
+	for(std::list<Edge>::iterator it=edges.edges.begin();it!=edges.edges.end();)
+	{
+		Edge e = *it;
+		if(e.a == this || e.b == this)
+		{
+			it = edges.edges.erase(it); //erase invalidate the iterator
+		}
+		else
+		{
+			it++;
+		}
+	}
+}
+
+#if FORWARD_ENABLED
+void PNode::hess_forward(unsigned int len, double** ret_vec)
+{
+	//it's a scalar
+	(*ret_vec) = new double[len];
+	std::fill_n(*ret_vec,len,0);
+	SV->push_back(this->pval);
+	assert(SV->size()==1);
+}
+#endif
+
+
+TYPE PNode::getType()
+{
+	return PNode_Type;
+}
+}
diff --git a/src/boost/libs/yap/example/autodiff_library/PNode.h b/src/boost/libs/yap/example/autodiff_library/PNode.h
new file mode 100644
index 00000000..58924d64
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/PNode.h
@@ -0,0 +1,47 @@
+/*
+ * PNode.h
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef PNODE_H_
+#define PNODE_H_
+
+#include "Node.h"
+namespace AutoDiff {
+
+using namespace std;
+class PNode: public Node {
+public:
+	PNode(double value);
+	virtual ~PNode();
+	void collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total);
+	void eval_function();
+	void grad_reverse_0();
+	void grad_reverse_1_init_adj();
+	void grad_reverse_1();
+	void update_adj(double& v);
+	void hess_forward(unsigned int len,double** ret_vec);
+	unsigned int hess_reverse_0();
+	void hess_reverse_0_get_values(unsigned int i,double& x,double& x_bar,double& w,double& w_bar);
+	void hess_reverse_1(unsigned int i);
+	void hess_reverse_1_init_x_bar(unsigned int);
+	void update_x_bar(unsigned int, double);
+	void update_w_bar(unsigned int, double);
+	void hess_reverse_1_get_xw(unsigned int, double&,double&);
+	void hess_reverse_get_x(unsigned int,double& x);
+	
+	void nonlinearEdges(EdgeSet&);
+
+	void inorder_visit(int level,ostream& oss);
+	string toString(int level);
+	TYPE getType();
+
+	double pval;
+
+};
+
+} // end namespace foo
+
+#endif /* PNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/README.md b/src/boost/libs/yap/example/autodiff_library/README.md
new file mode 100644
index 00000000..8f375446
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/README.md
@@ -0,0 +1,10 @@
+autodiff_library
+================ <\br>
+
+Automatic Differentiation Library <br>
+1. Very easy access and light weight c++/c library <br>
+2. Build computation graph as a DAG. <br>
+3. Provide function evaluation, reverse gradient, reverse Hessian-vector, forward Hessian computation calls.<br>
+4. State-of-the-art Object-Oriented Design and Implementation in C++ <br>
+5. A modified version of this library is integrated into the Parallel Structured Model Generator(PSMG)--an algebraic modelling langauge for Mathematical Programming.
+See project wiki for more detail.
diff --git a/src/boost/libs/yap/example/autodiff_library/Stack.cpp b/src/boost/libs/yap/example/autodiff_library/Stack.cpp
new file mode 100644
index 00000000..f0e69f84
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Stack.cpp
@@ -0,0 +1,58 @@
+/*
+ * Stack.cpp
+ *
+ *  Created on: 15 Apr 2013
+ *      Author: s0965328
+ */
+
+
+#include <cstddef>
+#include <math.h>
+#include <cassert>
+
+#include "Stack.h"
+
+namespace AutoDiff {
+
+
+Stack* Stack::vals = NULL;
+Stack* Stack::diff = NULL;
+
+Stack::Stack()
+{
+}
+
+Stack::~Stack() {
+	this->clear();
+}
+
+
+double Stack::pop_back()
+{
+	assert(this->lifo.size()!=0);
+	double v = this->lifo.top();
+	lifo.pop();
+	return v;
+}
+void Stack::push_back(double& v)
+{
+	assert(!isnan(v));
+	this->lifo.push(v);
+}
+double& Stack::peek()
+{
+	return this->lifo.top();
+}
+unsigned int Stack::size()
+{
+	return this->lifo.size();
+}
+
+void Stack::clear()
+{
+	while(!this->lifo.empty())
+	{
+		this->lifo.pop();
+	}
+}
+}
diff --git a/src/boost/libs/yap/example/autodiff_library/Stack.h b/src/boost/libs/yap/example/autodiff_library/Stack.h
new file mode 100644
index 00000000..30f5a3f0
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Stack.h
@@ -0,0 +1,38 @@
+/*
+ * Stack.h
+ *
+ *  Created on: 15 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef STACK_H_
+#define STACK_H_
+
+#include <stack>
+
+namespace AutoDiff {
+
+using namespace std;
+#define SV (Stack::vals)
+#define SD (Stack::diff)
+
+class Stack {
+public:
+	Stack();
+	double pop_back();
+	void push_back(double& v);
+	double& peek();
+	unsigned int size();
+	void clear();
+	virtual ~Stack();
+
+	stack<double> lifo;
+
+	static Stack* diff;
+	static Stack* vals;
+
+
+};
+
+}
+#endif /* STACK_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/Tape.cpp b/src/boost/libs/yap/example/autodiff_library/Tape.cpp
new file mode 100644
index 00000000..0a5682f3
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Tape.cpp
@@ -0,0 +1,16 @@
+/*
+ * Tape.cpp
+ *
+ *  Created on: 6 Nov 2013
+ *      Author: s0965328
+ */
+
+
+
+#include "Tape.h"
+
+namespace AutoDiff
+{
+	template<> Tape<unsigned int>* Tape<unsigned int>::indexTape = NULL;
+	template<> Tape<double>* Tape<double>::valueTape = NULL;
+}
diff --git a/src/boost/libs/yap/example/autodiff_library/Tape.h b/src/boost/libs/yap/example/autodiff_library/Tape.h
new file mode 100644
index 00000000..9ca62c4d
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/Tape.h
@@ -0,0 +1,97 @@
+/*
+ * Tape.h
+ *
+ *  Created on: 15 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef TAPE_H_
+#define TAPE_H_
+
+#include <vector>
+#include <string>
+#include <cassert>
+#include <sstream>
+#include <iostream>
+
+
+namespace AutoDiff {
+
+using namespace std;
+#define TT 	(Tape<double>::valueTape)
+#define II 	(Tape<unsigned int>::indexTape)
+
+template<typename T> class Tape {
+public:
+	Tape<T> () : index(0){};
+	T& at(const unsigned int index);
+	const T& get(const unsigned int index);
+	void set(T& v);
+	unsigned int size();
+	void clear();
+	bool empty();
+	string toString();
+	virtual ~Tape();
+
+	vector<T> vals;
+	unsigned int index;
+
+	static Tape<double>* valueTape;
+	static Tape<unsigned int>* indexTape;
+};
+
+
+template<typename T> Tape<T>::~Tape<T>()
+{
+	index = 0;
+	vals.clear();
+}
+
+template<typename T> T& Tape<T>::at(const unsigned int i)
+{
+	assert(this->vals.size()>i);
+	return vals[i];
+}
+template<typename T> const T& Tape<T>::get(const unsigned int i)
+{
+	assert(this->vals.size()>i);
+	return vals[i];
+}
+template <typename T> void Tape<T>::set(T& v)
+{
+	vals.push_back(v);
+	index++;
+}
+
+template<typename T> unsigned int Tape<T>::size()
+{
+	return this->vals.size();
+}
+
+template<typename T> bool Tape<T>::empty()
+{
+	return vals.empty();
+}
+
+template<typename T> void Tape<T>::clear()
+{
+	this->vals.clear();
+	this->index = 0;
+	assert(this->vals.size()==0);
+	assert(this->vals.empty());
+}
+
+template<typename T>  string Tape<T>::toString()
+{
+	assert(vals.size()>=index);
+	ostringstream oss;
+	oss<<"Tape size["<<vals.size()<<"]";
+	for(unsigned int i=0;i<vals.size();i++){
+		if(i%10==0) oss<<endl;
+		oss<<vals[i]<<",";
+	}
+	oss<<endl;
+	return oss.str();
+}
+}
+#endif /* TAPE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/UaryOPNode.cpp b/src/boost/libs/yap/example/autodiff_library/UaryOPNode.cpp
new file mode 100644
index 00000000..73e2711c
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/UaryOPNode.cpp
@@ -0,0 +1,375 @@
+/*
+ * UaryOPNode.cpp
+ *
+ *  Created on: 6 Nov 2013
+ *      Author: s0965328
+ */
+
+#include "UaryOPNode.h"
+#include "BinaryOPNode.h"
+#include "PNode.h"
+#include "Stack.h"
+#include "Tape.h"
+#include "Edge.h"
+#include "EdgeSet.h"
+#include "auto_diff_types.h"
+
+#include <list>
+
+using namespace std;
+
+namespace AutoDiff {
+
+UaryOPNode::UaryOPNode(OPCODE op_, Node* left): OPNode(op_,left) {
+}
+
+OPNode* UaryOPNode::createUnaryOpNode(OPCODE op, Node* left)
+{
+	assert(left!=NULL);
+	OPNode* node = NULL;
+	if(op == OP_SQRT)
+	{
+		double param = 0.5;
+		node = BinaryOPNode::createBinaryOpNode(OP_POW,left,new PNode(param));
+	}
+	else if(op == OP_NEG)
+	{
+		double param = -1;
+		node = BinaryOPNode::createBinaryOpNode(OP_TIMES,left,new PNode(param));
+	}
+	else
+	{
+		node = new UaryOPNode(op,left);
+	}
+	return node;
+}
+
+UaryOPNode::~UaryOPNode() {
+
+}
+
+
+void UaryOPNode::inorder_visit(int level,ostream& oss){
+	if(left!=NULL){
+		left->inorder_visit(level+1,oss);
+	}
+	oss<<this->toString(level)<<endl;
+}
+
+void UaryOPNode::collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total)
+{
+	total++;
+	if(left!=NULL){
+		left->collect_vnodes(nodes,total);
+	}
+}
+
+void UaryOPNode::eval_function()
+{
+	if(left!=NULL){
+		left->eval_function();
+	}
+	this->calc_eval_function();
+}
+
+//1. visiting left if not NULL
+//2. then, visiting right if not NULL
+//3. calculating the immediate derivative hu and hv
+void UaryOPNode::grad_reverse_0(){
+	assert(left!=NULL);
+	this->adj = 0;
+	left->grad_reverse_0();
+	this->calc_grad_reverse_0();
+}
+
+//right left - right most traversal
+void UaryOPNode::grad_reverse_1()
+{
+	assert(left!=NULL);
+	double l_adj = SD->pop_back()*this->adj;
+	left->update_adj(l_adj);
+	left->grad_reverse_1();
+}
+
+void UaryOPNode::calc_grad_reverse_0()
+{
+	assert(left!=NULL);
+	double hu = NaN_Double;
+	double lval = SV->pop_back();
+	double val = NaN_Double;
+	switch (op)
+	{
+	case OP_SIN:
+		val = sin(lval);
+		hu = cos(lval);
+		break;
+	case OP_COS:
+		val = cos(lval);
+		hu = -sin(lval);
+		break;
+	default:
+		cerr<<"error op not impl"<<endl;
+		break;
+	}
+	SV->push_back(val);
+	SD->push_back(hu);
+}
+
+void UaryOPNode::calc_eval_function()
+{
+	double lval = SV->pop_back();
+	double val = NaN_Double;
+	switch (op)
+	{
+	case OP_SIN:
+		assert(left!=NULL);
+		val = sin(lval);
+		break;
+	case OP_COS:
+		assert(left!=NULL);
+		val = cos(lval);
+		break;
+	default:
+		cerr<<"op["<<op<<"] not yet implemented!!"<<endl;
+		assert(false);
+		break;
+	}
+	SV->push_back(val);
+}
+
+void UaryOPNode::hess_reverse_0_init_n_in_arcs()
+{
+	this->left->hess_reverse_0_init_n_in_arcs();
+	this->Node::hess_reverse_0_init_n_in_arcs();
+}
+
+void UaryOPNode::hess_reverse_1_clear_index()
+{
+	this->left->hess_reverse_1_clear_index();
+	this->Node::hess_reverse_1_clear_index();
+}
+
+unsigned int UaryOPNode::hess_reverse_0()
+{
+	assert(left!=NULL);
+	if(index==0)
+	{
+		unsigned int lindex=0;
+		lindex = left->hess_reverse_0();
+		assert(lindex!=0);
+		II->set(lindex);
+		double lx,lx_bar,lw,lw_bar;
+		double x,x_bar,w,w_bar;
+		double l_dh;
+		switch(op)
+		{
+		case OP_SIN:
+			assert(left != NULL);
+			left->hess_reverse_0_get_values(lindex,lx,lx_bar,lw,lw_bar);
+			x = sin(lx);
+			x_bar = 0;
+			l_dh = cos(lx);
+			w = lw*l_dh;
+			w_bar = 0;
+			break;
+		case OP_COS:
+			assert(left!=NULL);
+			left->hess_reverse_0_get_values(lindex,lx,lx_bar,lw,lw_bar);
+			x = cos(lx);
+			x_bar = 0;
+			l_dh = -sin(lx);
+			w = lw*l_dh;
+			w_bar = 0;
+			break;
+		default:
+			cerr<<"op["<<op<<"] not yet implemented!"<<endl;
+			assert(false);
+			break;
+		}
+		TT->set(x);
+		TT->set(x_bar);
+		TT->set(w);
+		TT->set(w_bar);
+		TT->set(l_dh);
+		assert(TT->index == TT->index);
+		index = TT->index;
+	}
+	return index;
+}
+
+void UaryOPNode::hess_reverse_0_get_values(unsigned int i,double& x, double& x_bar, double& w, double& w_bar)
+{
+	--i; // skip the l_dh (ie, dh/du)
+	w_bar = TT->get(--i);
+	w = TT->get(--i);
+	x_bar = TT->get(--i);
+	x = TT->get(--i);
+}
+
+void UaryOPNode::hess_reverse_1(unsigned int i)
+{
+	n_in_arcs--;
+	if(n_in_arcs==0)
+	{
+		double lindex = II->get(--(II->index));
+	//	cout<<"li["<<lindex<<"]\t"<<this->toString(0)<<endl;
+		double l_dh = TT->get(--i);
+		double w_bar = TT->get(--i);
+		--i; //skip w
+		double x_bar = TT->get(--i);
+		--i; //skip x
+	//	cout<<"i["<<i<<"]"<<endl;
+
+		assert(left!=NULL);
+		left->update_x_bar(lindex,x_bar*l_dh);
+		double lw_bar = 0;
+		double lw = 0,lx = 0;
+		left->hess_reverse_1_get_xw(lindex,lw,lx);
+		switch(op)
+		{
+		case OP_SIN:
+			assert(l_dh == cos(lx));
+			lw_bar += w_bar*l_dh;
+			lw_bar += x_bar*lw*(-sin(lx));
+			break;
+		case OP_COS:
+			assert(l_dh == -sin(lx));
+			lw_bar += w_bar*l_dh;
+			lw_bar += x_bar*lw*(-cos(lx));
+			break;
+		default:
+			cerr<<"op["<<op<<"] not yet implemented!"<<endl;
+			break;
+		}
+		left->update_w_bar(lindex,lw_bar);
+		left->hess_reverse_1(lindex);
+	}
+}
+
+void UaryOPNode::hess_reverse_1_init_x_bar(unsigned int i)
+{
+	TT->at(i-4) = 1;
+}
+
+void UaryOPNode::update_x_bar(unsigned int i ,double v)
+{
+	TT->at(i-4) += v;
+}
+void UaryOPNode::update_w_bar(unsigned int i ,double v)
+{
+	TT->at(i-2) += v;
+}
+void UaryOPNode::hess_reverse_1_get_xw(unsigned int i,double& w,double& x)
+{
+	w = TT->get(i-3);
+	x = TT->get(i-5);
+}
+void UaryOPNode::hess_reverse_get_x(unsigned int i, double& x)
+{
+	x = TT->get(i-5);
+}
+
+void UaryOPNode::nonlinearEdges(EdgeSet& edges)
+{
+	for(list<Edge>::iterator it=edges.edges.begin();it!=edges.edges.end();)
+	{
+		Edge& e = *it;
+		if(e.a == this || e.b == this){
+			if(e.a == this && e.b == this)
+			{
+				Edge e1(left,left);
+				edges.insertEdge(e1);
+			}
+			else{
+				Node* o = e.a==this?e.b:e.a;
+				Edge e1(left,o);
+				edges.insertEdge(e1);
+			}
+			it = edges.edges.erase(it);
+		}
+		else
+		{
+			it++;
+		}
+	}
+
+	Edge e1(left,left);
+	switch(op)
+	{
+	case OP_SIN:
+		edges.insertEdge(e1);
+		break;
+	case OP_COS:
+		edges.insertEdge(e1);
+		break;
+	default:
+		cerr<<"op["<<op<<"] is not yet implemented !"<<endl;
+		assert(false);
+		break;
+	}
+	left->nonlinearEdges(edges);
+}
+
+#if FORWARD_ENABLED
+void UaryOPNode::hess_forward(unsigned int len, double** ret_vec)
+{
+	double* lvec = NULL;
+	if(left!=NULL){
+		left->hess_forward(len,&lvec);
+	}
+
+	*ret_vec = new double[len];
+	this->hess_forward_calc0(len,lvec,*ret_vec);
+	delete[] lvec;
+}
+
+void UaryOPNode::hess_forward_calc0(unsigned int& len, double* lvec, double* ret_vec)
+{
+	double hu = NaN_Double;
+	double lval = NaN_Double;
+	double val = NaN_Double;
+	unsigned int index = 0;
+	switch (op)
+	{
+	case OP_SIN:
+		assert(left!=NULL);
+		lval = SV->pop_back();
+		val = sin(lval);
+		SV->push_back(val);
+		hu = cos(lval);
+
+		double coeff;
+		coeff = -val; //=sin(left->val); -- and avoid cross initialisation
+		//calculate the first order derivatives
+		for(unsigned int i =0;i<AutoDiff::num_var;++i)
+		{
+			ret_vec[i] = hu*lvec[i] + 0;
+		}
+		//calculate the second order
+		index = AutoDiff::num_var;
+		for(unsigned int i=0;i<AutoDiff::num_var;++i)
+		{
+			for(unsigned int j=i;j<AutoDiff::num_var;++j)
+			{
+				ret_vec[index] = hu*lvec[index] + lvec[i] * coeff * lvec[j] + 0 + 0;
+				++index;
+			}
+		}
+		assert(index==len);
+		break;
+	default:
+		cerr<<"op["<<op<<"] not yet implemented!";
+		break;
+	}
+}
+#endif
+
+string UaryOPNode::toString(int level)
+{
+	ostringstream oss;
+	string s(level,'\t');
+	oss<<s<<"[UaryOPNode]("<<op<<")";
+	return oss.str();
+}
+
+} /* namespace AutoDiff */
diff --git a/src/boost/libs/yap/example/autodiff_library/UaryOPNode.h b/src/boost/libs/yap/example/autodiff_library/UaryOPNode.h
new file mode 100644
index 00000000..241cd992
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/UaryOPNode.h
@@ -0,0 +1,52 @@
+/*
+ * UaryOPNode.h
+ *
+ *  Created on: 6 Nov 2013
+ *      Author: s0965328
+ */
+
+#ifndef UARYOPNODE_H_
+#define UARYOPNODE_H_
+
+#include "OPNode.h"
+
+namespace AutoDiff {
+
+class UaryOPNode: public OPNode {
+public:
+	static OPNode* createUnaryOpNode(OPCODE op, Node* left);
+	virtual ~UaryOPNode();
+
+	void inorder_visit(int level,ostream& oss);
+	void collect_vnodes(boost::unordered_set<Node*> & nodes,unsigned int& total);
+	void eval_function();
+
+	void grad_reverse_0();
+	void grad_reverse_1();
+#if FORWARD_ENABLED
+	void hess_forward(unsigned int len, double** ret_vec);
+#endif
+	unsigned int hess_reverse_0();
+	void hess_reverse_0_init_n_in_arcs();
+	void hess_reverse_0_get_values(unsigned int i,double& x, double& x_bar, double& w, double& w_bar);
+	void hess_reverse_1(unsigned int i);
+	void hess_reverse_1_init_x_bar(unsigned int);
+	void update_x_bar(unsigned int, double v);
+	void update_w_bar(unsigned int, double v);
+	void hess_reverse_1_get_xw(unsigned int, double&,double&);
+	void hess_reverse_get_x(unsigned int,double& x);
+	void hess_reverse_1_clear_index();
+
+	void nonlinearEdges(EdgeSet&);
+
+	string toString(int level);
+
+private:
+	UaryOPNode(OPCODE op, Node* left);
+	void calc_eval_function();
+	void calc_grad_reverse_0();
+	void hess_forward_calc0(unsigned int& len, double* lvec,double* ret_vec);
+};
+
+} /* namespace AutoDiff */
+#endif /* UARYOPNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/VNode.cpp b/src/boost/libs/yap/example/autodiff_library/VNode.cpp
new file mode 100644
index 00000000..285af01f
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/VNode.cpp
@@ -0,0 +1,149 @@
+/*
+ * VNode.cpp
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#include "VNode.h"
+#include "Tape.h"
+#include "Stack.h"
+
+using namespace std;
+
+namespace AutoDiff {
+
+#if FORWARD_ENABLED
+int VNode::DEFAULT_ID = -1;
+#endif
+
+VNode::VNode(double v) : ActNode(), val(v),u(NaN_Double)
+#if FORWARD_ENABLED
+,id(DEFAULT_ID)
+#endif
+{
+}
+
+VNode::~VNode() {
+}
+
+void VNode::collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total)
+{
+	total++;
+	boost::unordered_set<Node*>::iterator it = nodes.find(this);
+	if(it==nodes.end())
+		nodes.insert(this);
+}
+
+void VNode::inorder_visit(int level,ostream& oss)
+{
+	oss<<this->toString(level)<<endl;
+}
+
+void VNode::eval_function()
+{
+	SV->push_back(val);
+}
+
+string VNode::toString(int level)
+{
+	ostringstream oss;
+	string s(level,'\t');
+	oss<<s<<"[VNode](index:"<<index<<",val:"<<val<<",u:"<<u<<") - "<<this;
+	return oss.str();
+}
+
+void VNode::grad_reverse_0()
+{
+	this->adj = 0;
+	SV->push_back(val);
+}
+
+void VNode::grad_reverse_1()
+{
+	//do nothing
+	//this is a leaf node
+}
+
+#if FORWARD_ENABLED
+void VNode::hess_forward(unsigned int len, double** ret_vec)
+{
+	assert(id!=DEFAULT_ID);
+	(*ret_vec) = new double[len];
+	std::fill_n(*ret_vec,len,0);
+	(*ret_vec)[id]=1;
+	SV->push_back(this->val);
+}
+#endif
+
+unsigned int VNode::hess_reverse_0()
+{
+	if(index==0)
+	{//this node is not on tape
+		double nan = NaN_Double;
+		TT->set(val);  	//x_i
+		TT->set(nan);		//x_bar_i
+		TT->set(u);    	//w_i
+		TT->set(nan);    	//w_bar_i
+		index = TT->index;
+	}
+//	cout<<toString(0)<<"  -- "<<index<<endl;
+	return index;
+}
+
+void VNode::hess_reverse_0_get_values(unsigned int i,double& x, double& x_bar, double& w, double& w_bar)
+{
+	w_bar = TT->get(--i);
+	w = TT->get(--i);
+	x_bar = TT->get(--i);
+	x = TT->get(--i);
+}
+
+void VNode::hess_reverse_1(unsigned int i)
+{
+	n_in_arcs--;
+	//leaf node do nothing
+}
+
+void VNode::hess_reverse_1_init_x_bar(unsigned int i)
+{
+	TT->at(i-3) = 1;
+}
+
+void VNode::update_x_bar(unsigned int i ,double v)
+{
+//	cout<<toString(0)<<"  --- "<<__FUNCTION__<<"  v="<<TT->at(i-3)<<"+"<<v<<endl;
+	TT->at(i-3) = isnan(TT->get(i-3))? v: TT->get(i-3) + v;
+}
+
+void VNode::update_w_bar(unsigned int i,double v)
+{
+//	cout<<toString(0)<<"  --- "<<__FUNCTION__<<"  v="<<TT->at(i-1)<<"+"<<v<<endl;
+	TT->at(i-1) = isnan(TT->get(i-1))? v: TT->get(i-1) + v;
+}
+void VNode::hess_reverse_1_get_xw(unsigned int i, double& w,double& x)
+{
+	//cout<<toString(0)<<"  --- "<<__FUNCTION__<<"  w="<<TT->get(i-2)<<"-- "<<"x="<<TT->get(i-4)<<endl;
+	w = TT->get(i-2);
+	x = TT->get(i-4);
+}
+void VNode::hess_reverse_get_x(unsigned int i ,double& x)
+{
+	x = TT->get(i-4);
+}
+
+void VNode::nonlinearEdges(EdgeSet& edges)
+{
+//	for(list<Edge>::iterator it = edges.edges.begin();it!=edges.edges.end();)
+//	{
+//		Edge e=*it;
+//
+//	}
+}
+
+
+TYPE VNode::getType()
+{
+	return VNode_Type;
+}
+}
diff --git a/src/boost/libs/yap/example/autodiff_library/VNode.h b/src/boost/libs/yap/example/autodiff_library/VNode.h
new file mode 100644
index 00000000..d9673d4b
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/VNode.h
@@ -0,0 +1,52 @@
+/*
+ * VNode.h
+ *
+ *  Created on: 8 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef VNODE_H_
+#define VNODE_H_
+
+#include "ActNode.h"
+
+namespace AutoDiff {
+class VNode: public ActNode {
+public:
+	VNode(double v=NaN_Double);
+	virtual ~VNode();
+	void collect_vnodes(boost::unordered_set<Node*>& nodes,unsigned int& total);
+	void eval_function();
+	void grad_reverse_0();
+	void grad_reverse_1();
+	unsigned int hess_reverse_0();
+	void hess_reverse_0_get_values(unsigned int i,double& x, double& x_bar, double& w, double& w_bar);
+	void hess_reverse_1(unsigned int i);
+	void hess_reverse_1_init_x_bar(unsigned int);
+	void update_x_bar(unsigned int,double);
+	void update_w_bar(unsigned int,double);
+	void hess_reverse_1_get_xw(unsigned int,double&,double&);
+	void hess_reverse_get_x(unsigned int,double& x);
+
+	void nonlinearEdges(EdgeSet&);
+
+	void inorder_visit(int level,ostream& oss);
+	string toString(int level);
+	TYPE getType();
+
+#if FORWARD_ENABLED
+	void hess_forward(unsigned int nvar, double** ret_vec);
+	//! used for only forward hessian
+	//! the id has to be assigned starting from 0
+	int id;
+	static int DEFAULT_ID;
+#endif
+	double val;
+	double u;
+
+
+};
+
+} // end namespace foo
+
+#endif /* VNODE_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/auto_diff_types.h b/src/boost/libs/yap/example/autodiff_library/auto_diff_types.h
new file mode 100644
index 00000000..b24c59a1
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/auto_diff_types.h
@@ -0,0 +1,26 @@
+/*
+ * auto_diff_types.h
+ *
+ *  Created on: 18 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef AUTO_DIFF_TYPES_H_
+#define AUTO_DIFF_TYPES_H_
+
+namespace AutoDiff{
+
+#define FORWARD_ENABLED 0
+#if FORWARD_ENABLED
+extern unsigned int num_var;
+#endif
+
+#define NaN_Double std::numeric_limits<double>::quiet_NaN()
+
+typedef enum { OPNode_Type=0, VNode_Type, PNode_Type} TYPE;
+
+
+typedef enum {OP_PLUS=0, OP_MINUS, OP_TIMES, OP_DIVID, OP_SIN, OP_COS, OP_SQRT, OP_POW, OP_NEG} OPCODE;
+
+}
+#endif /* AUTO_DIFF_TYPES_H_ */
diff --git a/src/boost/libs/yap/example/autodiff_library/autodiff.cpp b/src/boost/libs/yap/example/autodiff_library/autodiff.cpp
new file mode 100644
index 00000000..5fae3686
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/autodiff.cpp
@@ -0,0 +1,335 @@
+//============================================================================
+// Name        : autodiff.cpp
+// Author      : 
+// Version     :
+// Copyright   : Your copyright notice
+// Description : Hello World in C++, Ansi-style
+//============================================================================
+
+#include <iostream>
+#include <sstream>
+#include <numeric>
+#include <boost/foreach.hpp>
+#include "autodiff.h"
+#include "Stack.h"
+#include "Tape.h"
+#include "BinaryOPNode.h"
+#include "UaryOPNode.h"
+
+using namespace std;
+
+namespace AutoDiff
+{
+
+#if FORWARD_ENABLED
+
+unsigned int num_var = 0;
+
+void hess_forward(Node* root, unsigned int nvar, double** hess_mat)
+{
+	assert(nvar == num_var);
+	unsigned int len = (nvar+3)*nvar/2;
+	root->hess_forward(len,hess_mat);
+}
+
+#endif
+
+
+PNode* create_param_node(double value){
+	return new PNode(value);
+}
+VNode* create_var_node(double v)
+{
+	return new VNode(v);
+}
+OPNode* create_binary_op_node(OPCODE code, Node* left, Node* right)
+{
+	return BinaryOPNode::createBinaryOpNode(code,left,right);
+}
+OPNode* create_uary_op_node(OPCODE code, Node* left)
+{
+	return UaryOPNode::createUnaryOpNode(code,left);
+}
+double eval_function(Node* root)
+{
+	assert(SD->size()==0);
+	assert(SV->size()==0);
+	root->eval_function();
+	assert(SV->size()==1);
+	double val = SV->pop_back();
+	return val;
+}
+
+double grad_reverse(Node* root,vector<Node*>& vnodes, vector<double>& grad)
+{
+	grad.clear();
+	BOOST_FOREACH(Node* node, vnodes)
+	{
+		assert(node->getType()==VNode_Type);
+		static_cast<VNode*>(node)->adj = NaN_Double;
+	}
+
+	assert(SD->size()==0);
+	root->grad_reverse_0();
+	assert(SV->size()==1);
+	root->grad_reverse_1_init_adj();	
+	root->grad_reverse_1();
+	assert(SD->size()==0);
+	double val = SV->pop_back();
+	assert(SV->size()==0);
+	//int i=0;
+	BOOST_FOREACH(Node* node, vnodes)
+	{
+		assert(node->getType()==VNode_Type);
+		grad.push_back(static_cast<VNode*>(node)->adj);
+		static_cast<VNode*>(node)->adj = NaN_Double;
+	}
+	assert(grad.size()==vnodes.size());
+	//all nodes are VNode and adj == NaN_Double -- this reset adj for this expression tree by root
+	return val;
+}
+
+double grad_reverse(Node* root, vector<Node*>& vnodes, col_compress_matrix_row& rgrad)
+{
+	BOOST_FOREACH(Node* node, vnodes)
+	{
+		assert(node->getType()==VNode_Type);
+		static_cast<VNode*>(node)->adj = NaN_Double;
+	}
+	assert(SD->size()==0);
+	root->grad_reverse_0();
+	assert(SV->size()==1);
+	root->grad_reverse_1_init_adj();
+	root->grad_reverse_1();
+	assert(SD->size()==0);
+	double val = SV->pop_back();
+	assert(SV->size()==0);
+	unsigned int i =0;
+	BOOST_FOREACH(Node* node, vnodes)
+	{
+		assert((node)->getType()==VNode_Type);
+		double diff = static_cast<VNode*>(node)->adj;
+		if(!isnan(diff)){
+			rgrad(i) = diff;
+			static_cast<VNode*>(node)->adj = NaN_Double;
+		}
+		i++;
+	}
+	//all nodes are VNode and adj == NaN_Double -- this reset adj for this expression tree by root
+	assert(i==vnodes.size());
+	return val;
+}
+
+double hess_reverse(Node* root,vector<Node*>& vnodes,vector<double>& dhess)
+{
+	TT->clear();
+	II->clear();
+	assert(TT->empty());
+	assert(II->empty());
+	assert(TT->index==0);
+	assert(II->index==0);
+	dhess.clear();
+
+//	for(vector<Node*>::iterator it=nodes.begin();it!=nodes.end();it++)
+//	{
+//		assert((*it)->getType()==VNode_Type);
+//		(*it)->index = 0;
+//	} //this work complete in hess-reverse_0_init_index
+
+	assert(root->n_in_arcs == 0);
+	root->hess_reverse_0_init_n_in_arcs();
+	assert(root->n_in_arcs == 1);
+	root->hess_reverse_0();
+	double val = NaN_Double;
+	root->hess_reverse_get_x(TT->index,val);
+//	cout<<TT->toString();
+//	cout<<endl;
+//	cout<<II->toString();
+//	cout<<"======================================= hess_reverse_0"<<endl;
+	root->hess_reverse_1_init_x_bar(TT->index);
+	assert(root->n_in_arcs == 1);
+	root->hess_reverse_1(TT->index);
+	assert(root->n_in_arcs == 0);
+	assert(II->index==0);
+//	cout<<TT->toString();
+//	cout<<endl;
+//	cout<<II->toString();
+//	cout<<"======================================= hess_reverse_1"<<endl;
+
+	for(vector<Node*>::iterator it=vnodes.begin();it!=vnodes.end();it++)
+	{
+		assert((*it)->getType()==VNode_Type);
+		dhess.push_back(TT->get((*it)->index-1));
+	}
+
+	TT->clear();
+	II->clear();
+	root->hess_reverse_1_clear_index();
+	return val;
+}
+
+double hess_reverse(Node* root,vector<Node*>& vnodes,col_compress_matrix_col& chess)
+{
+	TT->clear();
+	II->clear();
+	assert(TT->empty());
+	assert(II->empty());
+	assert(TT->index==0);
+	assert(II->index==0);
+
+//	for(vector<Node*>::iterator it=nodes.begin();it!=nodes.end();it++)
+//	{
+//		assert((*it)->getType()==VNode_Type);
+//		(*it)->index = 0;
+//	} //this work complete in hess-reverse_0_init_index
+
+	assert(root->n_in_arcs == 0);
+	//reset node index and n_in_arcs - for the Tape location
+	root->hess_reverse_0_init_n_in_arcs();
+	assert(root->n_in_arcs == 1);
+	root->hess_reverse_0();
+	double val = NaN_Double;
+	root->hess_reverse_get_x(TT->index,val);
+//	cout<<TT->toString();
+//	cout<<endl;
+//	cout<<II->toString();
+//	cout<<"======================================= hess_reverse_0"<<endl;
+	root->hess_reverse_1_init_x_bar(TT->index);
+	assert(root->n_in_arcs == 1);
+	root->hess_reverse_1(TT->index);
+	assert(root->n_in_arcs == 0);
+	assert(II->index==0);
+//	cout<<TT->toString();
+//	cout<<endl;
+//	cout<<II->toString();
+//	cout<<"======================================= hess_reverse_1"<<endl;
+
+	unsigned int i =0;
+	BOOST_FOREACH(Node* node, vnodes)
+	{
+		assert(node->getType() == VNode_Type);
+		//node->index = 0 means this VNode is not in the tree
+		if(node->index!=0)
+		{
+			double hess = TT->get(node->index -1);
+			if(!isnan(hess))
+			{
+				chess(i) = chess(i) + hess;
+			}
+		}
+		i++;
+	}
+	assert(i==vnodes.size());
+	root->hess_reverse_1_clear_index();
+	TT->clear();
+	II->clear();
+	return val;
+}
+
+unsigned int nzGrad(Node* root)
+{
+	unsigned int nzgrad,total = 0;
+	boost::unordered_set<Node*> nodes;
+	root->collect_vnodes(nodes,total);
+	nzgrad = nodes.size();
+	return nzgrad;
+}
+
+/*
+ * number of non-zero gradient in constraint tree root that also belong to vSet
+ */
+unsigned int nzGrad(Node* root, boost::unordered_set<Node*>& vSet)
+{
+	unsigned int nzgrad=0, total=0;
+	boost::unordered_set<Node*> vnodes;
+	root->collect_vnodes(vnodes,total);
+	//cout<<"nzGrad - vnodes size["<<vnodes.size()<<"] -- total node["<<total<<"]"<<endl;
+	for(boost::unordered_set<Node*>::iterator it=vnodes.begin();it!=vnodes.end();it++)
+	{
+		Node* n = *it;
+		if(vSet.find(n) != vSet.end())
+		{
+			nzgrad++;
+		}
+	}
+	return nzgrad;
+}
+
+void nonlinearEdges(Node* root, EdgeSet& edges)
+{
+	root->nonlinearEdges(edges);
+}
+
+unsigned int nzHess(EdgeSet& eSet,boost::unordered_set<Node*>& set1, boost::unordered_set<Node*>& set2)
+{
+	list<Edge>::iterator i = eSet.edges.begin();
+	for(;i!=eSet.edges.end();)
+	{
+		Edge e =*i;
+		Node* a = e.a;
+		Node* b = e.b;
+		if((set1.find(a)!=set1.end() && set2.find(b)!=set2.end())
+			||
+			(set1.find(b)!=set1.end() && set2.find(a)!=set2.end()))
+		{
+			//e is connected between set1 and set2
+			i++;
+		}
+		else
+		{
+			i = eSet.edges.erase(i);
+		}
+	}
+	unsigned int diag=eSet.numSelfEdges();
+	unsigned int nzHess = (eSet.size())*2 - diag;
+	return nzHess;
+}
+
+unsigned int nzHess(EdgeSet& edges)
+{
+	unsigned int diag=edges.numSelfEdges();
+	unsigned int nzHess = (edges.size())*2 - diag;
+	return nzHess;
+}
+
+unsigned int numTotalNodes(Node* root)
+{
+	unsigned int total = 0;
+	boost::unordered_set<Node*> nodes;
+	root->collect_vnodes(nodes,total);
+	return total;
+}
+
+string tree_expr(Node* root)
+{
+	ostringstream oss;
+	oss<<"visiting tree == "<<endl;
+	int level = 0;
+	root->inorder_visit(level,oss);
+	return oss.str();
+}
+
+void print_tree(Node* root)
+{
+	cout<<"visiting tree == "<<endl;
+	int level = 0;
+	root->inorder_visit(level,cout);
+}
+
+void autodiff_setup()
+{
+	Stack::diff = new Stack();
+	Stack::vals = new Stack();
+	Tape<unsigned int>::indexTape = new Tape<unsigned int>();
+	Tape<double>::valueTape = new Tape<double>();
+}
+
+void autodiff_cleanup()
+{
+	delete Stack::diff;
+	delete Stack::vals;
+	delete Tape<unsigned int>::indexTape;
+	delete Tape<double>::valueTape;
+}
+
+} //AutoDiff namespace end
diff --git a/src/boost/libs/yap/example/autodiff_library/autodiff.h b/src/boost/libs/yap/example/autodiff_library/autodiff.h
new file mode 100644
index 00000000..738cb3f9
--- /dev/null
+++ b/src/boost/libs/yap/example/autodiff_library/autodiff.h
@@ -0,0 +1,114 @@
+/*
+ * autodiff.h
+ *
+ *  Created on: 16 Apr 2013
+ *      Author: s0965328
+ */
+
+#ifndef AUTODIFF_H_
+#define AUTODIFF_H_
+#include <boost/unordered_set.hpp>
+#include <boost/numeric/ublas/matrix_proxy.hpp>
+#include <boost/numeric/ublas/matrix.hpp>
+#include <boost/numeric/ublas/matrix_sparse.hpp>
+#include <boost/numeric/ublas/io.hpp>
+#include "auto_diff_types.h"
+#include "Node.h"
+#include "VNode.h"
+#include "OPNode.h"
+#include "PNode.h"
+#include "ActNode.h"
+#include "EdgeSet.h"
+
+
+/*
+ * + Function and Gradient Evaluation
+ * The tapeless implementation for function and derivative evaluation
+ * Advantage for tapeless:
+ * 			Low memory usage
+ * 			Function evaluation use one stack
+ * 			Gradient evaluation use two stack.
+ * Disadvantage for tapeless:
+ * 			Inefficient if the expression tree have repeated nodes.
+ * 			for example:
+ * 						 root
+ * 						 /  \
+ * 						*    *
+ * 					   / \	/ \
+ * 				      x1 x1 x1 x1
+ * 				      Tapeless implementation will go through all the edges.
+ * 				      ie. adjoint of x will be updated 4 times for the correct
+ * 				      gradient of x1.While the tape implemenation can discovery this
+ * 				      dependence and update adjoint of x1 just twice. The computational
+ * 				      graph (DAG) for a taped implemenation will be look like bellow.
+ * 				       root
+ * 				        /\
+ * 				        *
+ * 				        /\
+ * 				        x1
+ *
+ * + Forward Hessian Evaluation:
+ * This is an inefficient implementation of the forward Hessian method. It will evaluate the diagonal
+ * and upper triangular of the Hessian. The gradient is also evaluation in the same routine. The result
+ * will be returned in an array.
+ * To use this method, one have to provide a len parameter. len = (nvar+3)*nvar/2 where nvar is the number
+ * of independent variables. ie. x_1 x_2 ... x_nvar. And the varaible id need to be a consequent integer start
+ * with 0.
+ * ret_vec will contains len number of doubles. Where the first nvar elements is the gradient vector,
+ * and the rest of (nvar+1)*nvar/2 elements are the upper/lower plus the diagonal part of the Hessian matrix
+ * in row format.
+ * This algorithm is inefficient, because at each nodes, it didn't check the dependency of the independent
+ * variables up to the current node. (or it is hard to do so for this setup). Therefore, it computes a full
+ * for loops over each independent variable (ie. assume they are all dependent), for those independent
+ * variables that are not dependent at the current node, zero will be produced by computation.
+ * By default the forward mode hessian routing is disabled. To enable the forward hessian interface, the
+ * compiler marco FORWARD_ENABLED need to be set equal to 1 in auto_diff_types.h
+ *
+ * + Reverse Hessian*Vector Evaluation:
+ * Simple, building a tape in the forward pass, and a reverse pass will evaluate the Hessian*vector. The implemenation
+ * also discovery the repeated subexpression and use one piece of memory on the tape for the same subexpression. This
+ * allow efficient evaluation, because the repeated subexpression only evaluate once in the forward and reverse pass.
+ * This algorithm can be called n times to compute a full Hessian, where n equals the number of independent
+ * variables.
+ * */
+
+typedef boost::numeric::ublas::compressed_matrix<double,boost::numeric::ublas::column_major,0,std::vector<std::size_t>,std::vector<double> >  col_compress_matrix;
+typedef boost::numeric::ublas::matrix_row<col_compress_matrix > col_compress_matrix_row;
+typedef boost::numeric::ublas::matrix_column<col_compress_matrix  > col_compress_matrix_col;
+
+namespace AutoDiff{
+
+	//node creation methods
+	extern PNode* create_param_node(double value);
+	extern VNode* create_var_node(double v=NaN_Double);
+	extern OPNode* create_uary_op_node(OPCODE code, Node* left);
+	extern OPNode* create_binary_op_node(OPCODE code, Node* left,Node* right);
+
+	//single constraint version
+	extern double eval_function(Node* root);
+	extern unsigned int nzGrad(Node* root);
+	extern double grad_reverse(Node* root,vector<Node*>& nodes, vector<double>& grad);
+	extern unsigned int nzHess(EdgeSet&);
+	extern double hess_reverse(Node* root, vector<Node*>& nodes, vector<double>& dhess);
+
+	//multiple constraints version
+	extern unsigned int nzGrad(Node* root, boost::unordered_set<Node*>& vnodes);
+	extern double grad_reverse(Node* root, vector<Node*>& nodes, col_compress_matrix_row& rgrad);
+	extern unsigned int nzHess(EdgeSet&,boost::unordered_set<Node*>& set1, boost::unordered_set<Node*>& set2);
+	extern double hess_reverse(Node* root, vector<Node*>& nodes, col_compress_matrix_col& chess);
+
+#if FORWARD_ENDABLED
+	//forward methods
+	extern void hess_forward(Node* root, unsigned int nvar, double** hess_mat);
+#endif
+
+	//utiliy methods
+	extern void nonlinearEdges(Node* root, EdgeSet& edges);
+	extern unsigned int numTotalNodes(Node*);
+	extern string tree_expr(Node* root);
+	extern void print_tree(Node* root);
+	extern void autodiff_setup();
+	extern void autodiff_cleanup();
+};
+
+#endif /* AUTODIFF_H_ */
diff --git a/src/boost/libs/yap/example/calc1.cpp b/src/boost/libs/yap/example/calc1.cpp
new file mode 100644
index 00000000..20c869ba
--- /dev/null
+++ b/src/boost/libs/yap/example/calc1.cpp
@@ -0,0 +1,27 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ calc1
+#include <boost/yap/expression.hpp>
+
+#include <iostream>
+
+
+int main ()
+{
+    using namespace boost::yap::literals;
+
+    // Displays "5"
+    std::cout << evaluate( 1_p + 2.0, 3.0 ) << std::endl;
+
+    // Displays "6"
+    std::cout << evaluate( 1_p * 2_p, 3.0, 2.0 ) << std::endl;
+
+    // Displays "0.5"
+    std::cout << evaluate( (1_p - 2_p) / 2_p, 3.0, 2.0 ) << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/calc2a.cpp b/src/boost/libs/yap/example/calc2a.cpp
new file mode 100644
index 00000000..8d28e5bf
--- /dev/null
+++ b/src/boost/libs/yap/example/calc2a.cpp
@@ -0,0 +1,45 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ calc2a
+#include <boost/yap/expression.hpp>
+
+#include <iostream>
+
+
+int main ()
+{
+    using namespace boost::yap::literals;
+
+    auto expr_1 = 1_p + 2.0;
+
+    auto expr_1_fn = [expr_1](auto &&... args) {
+        return evaluate(expr_1, args...);
+    };
+
+    auto expr_2 = 1_p * 2_p;
+
+    auto expr_2_fn = [expr_2](auto &&... args) {
+        return evaluate(expr_2, args...);
+    };
+
+    auto expr_3 = (1_p - 2_p) / 2_p;
+
+    auto expr_3_fn = [expr_3](auto &&... args) {
+        return evaluate(expr_3, args...);
+    };
+
+    // Displays "5"
+    std::cout << expr_1_fn(3.0) << std::endl;
+
+    // Displays "6"
+    std::cout << expr_2_fn(3.0, 2.0) << std::endl;
+
+    // Displays "0.5"
+    std::cout << expr_3_fn(3.0, 2.0) << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/calc2b.cpp b/src/boost/libs/yap/example/calc2b.cpp
new file mode 100644
index 00000000..cad5b913
--- /dev/null
+++ b/src/boost/libs/yap/example/calc2b.cpp
@@ -0,0 +1,27 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ calc2b
+#include <boost/yap/expression.hpp>
+
+#include <iostream>
+
+
+int main ()
+{
+    using namespace boost::yap::literals;
+
+    // Displays "5"
+    std::cout << make_expression_function(1_p + 2.0)(3.0) << std::endl;
+
+    // Displays "6"
+    std::cout << make_expression_function(1_p * 2_p)(3.0, 2.0) << std::endl;
+
+    // Displays "0.5"
+    std::cout << make_expression_function((1_p - 2_p) / 2_p)(3.0, 2.0) << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/calc3.cpp b/src/boost/libs/yap/example/calc3.cpp
new file mode 100644
index 00000000..7f0f55b7
--- /dev/null
+++ b/src/boost/libs/yap/example/calc3.cpp
@@ -0,0 +1,100 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ calc3
+#include <boost/yap/expression.hpp>
+
+#include <boost/hana/maximum.hpp>
+
+#include <iostream>
+
+
+// Look! A transform!  This one transforms the expression tree into the arity
+// of the expression, based on its placeholders.
+//[ calc3_get_arity_xform
+struct get_arity
+{
+    // Base case 1: Match a placeholder terminal, and return its arity as the
+    // result.
+    template <long long I>
+    boost::hana::llong<I> operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                                      boost::yap::placeholder<I>)
+    { return boost::hana::llong_c<I>; }
+
+    // Base case 2: Match any other terminal.  Return 0; non-placeholders do
+    // not contribute to arity.
+    template <typename T>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T &&)
+    {
+        using namespace boost::hana::literals;
+        return 0_c;
+    }
+
+    // Recursive case: Match any expression not covered above, and return the
+    // maximum of its children's arities.
+    template <boost::yap::expr_kind Kind, typename... Arg>
+    auto operator() (boost::yap::expr_tag<Kind>, Arg &&... arg)
+    {
+        return boost::hana::maximum(
+            boost::hana::make_tuple(
+                boost::yap::transform(
+                    boost::yap::as_expr(std::forward<Arg>(arg)),
+                    get_arity{}
+                )...
+            )
+        );
+    }
+};
+//]
+
+int main ()
+{
+    using namespace boost::yap::literals;
+
+    // These lambdas wrap our expressions as callables, and allow us to check
+    // the arity of each as we call it.
+
+    auto expr_1 = 1_p + 2.0;
+
+    auto expr_1_fn = [expr_1](auto &&... args) {
+        auto const arity = boost::yap::transform(expr_1, get_arity{});
+        static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
+        return evaluate(expr_1, args...);
+    };
+
+    auto expr_2 = 1_p * 2_p;
+
+    auto expr_2_fn = [expr_2](auto &&... args) {
+        auto const arity = boost::yap::transform(expr_2, get_arity{});
+        static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
+        return evaluate(expr_2, args...);
+    };
+
+    auto expr_3 = (1_p - 2_p) / 2_p;
+
+    auto expr_3_fn = [expr_3](auto &&... args) {
+        auto const arity = boost::yap::transform(expr_3, get_arity{});
+        static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
+        return evaluate(expr_3, args...);
+    };
+
+    // Displays "5"
+    std::cout << expr_1_fn(3.0) << std::endl;
+
+    // Displays "6"
+    std::cout << expr_2_fn(3.0, 2.0) << std::endl;
+
+    // Displays "0.5"
+    std::cout << expr_3_fn(3.0, 2.0) << std::endl;
+
+    // Static-asserts with "Called with wrong number of args."
+    //std::cout << expr_3_fn(3.0) << std::endl;
+
+    // Static-asserts with "Called with wrong number of args."
+    //std::cout << expr_3_fn(3.0, 2.0, 1.0) << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/future_group.cpp b/src/boost/libs/yap/example/future_group.cpp
new file mode 100644
index 00000000..15c980f0
--- /dev/null
+++ b/src/boost/libs/yap/example/future_group.cpp
@@ -0,0 +1,129 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ future_group
+#include <boost/yap/algorithm.hpp>
+
+#include <boost/hana/concat.hpp>
+
+
+// A custom expression template for future groups.  It supports operators ||
+// and &&.
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct future_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    future_expr (Tuple && tuple) :
+        elements (std::forward<Tuple &&>(tuple))
+    {}
+
+    Tuple elements;
+
+    // Returns the transformed/flattened expression.
+    auto get () const;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(logical_or, future_expr, future_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(logical_and, future_expr, future_expr)
+
+// A special-cased future terminal that matches the semantics from the
+// original Proto example.
+template <typename T>
+struct future :
+    future_expr<boost::yap::expr_kind::terminal, boost::hana::tuple<T>>
+{
+    future (T const & t = T()) :
+        future_expr<boost::yap::expr_kind::terminal, boost::hana::tuple<T>> (boost::hana::tuple<T>{t})
+    {}
+
+    T get () const
+    { return boost::yap::value(*this); }
+};
+
+template <typename T>
+using remove_cv_ref_t = std::remove_cv_t<std::remove_reference_t<T>>;
+
+// A transform that flattens future expressions into a tuple.
+struct future_transform
+{
+    // Transform a terminal into its contained tuple.
+    template <typename T>
+    auto operator() (
+        future_expr<
+            boost::yap::expr_kind::terminal,
+            boost::hana::tuple<T>
+        > const & term
+    ) {
+        return term.elements;
+    }
+
+//[ expr_xform
+    // Transform left || right -> transform(left).
+    template <typename T, typename U>
+    auto operator() (
+        future_expr<
+            boost::yap::expr_kind::logical_or,
+            boost::hana::tuple<T, U>
+        > const & or_expr
+    ) {
+        // Recursively transform the left side, and return the result.
+        // Without the recursion, we might return a terminal expression here
+        // insead of a tuple.
+        return boost::yap::transform(boost::yap::left(or_expr), *this);
+    }
+//]
+
+    // Transform left && right -> concat(transform(left), transform(right)).
+    template <typename T, typename U>
+    auto operator() (
+        future_expr<
+            boost::yap::expr_kind::logical_and,
+            boost::hana::tuple<T, U>
+        > const & and_expr
+    ) {
+        // Recursively transform each side, then combine the resulting tuples
+        // into a single tuple result.
+        return boost::hana::concat(
+            boost::yap::transform(boost::yap::left(and_expr), *this),
+            boost::yap::transform(boost::yap::right(and_expr), *this)
+        );
+    }
+};
+
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+auto future_expr<Kind, Tuple>::get () const
+{ return boost::yap::transform(*this, future_transform{}); }
+
+
+// TEST CASES
+struct A {};
+struct B {};
+struct C {};
+
+// Called "vector" just so the code in main() will match the original Proto
+// example.
+template <typename ...T>
+using vector = boost::hana::tuple<T...>;
+
+int main()
+{
+    future<A> a;
+    future<B> b;
+    future<C> c;
+    future<vector<A,B> > ab;
+
+    // Verify that various future groups have the
+    // correct return types.
+    A                       t0 = a.get();
+    vector<A, B, C>         t1 = (a && b && c).get();
+    vector<A, C>            t2 = ((a || a) && c).get();
+    vector<A, B, C>         t3 = ((a && b || a && b) && c).get();
+    vector<vector<A, B>, C> t4 = ((ab || ab) && c).get();
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/hello_world.cpp b/src/boost/libs/yap/example/hello_world.cpp
new file mode 100644
index 00000000..f509078e
--- /dev/null
+++ b/src/boost/libs/yap/example/hello_world.cpp
@@ -0,0 +1,19 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[hello_world
+
+#include <boost/yap/expression.hpp>
+
+#include <iostream>
+
+
+int main ()
+{
+    evaluate(boost::yap::make_terminal(std::cout) << "Hello" << ',' << " world!\n");
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/hello_world_redux.cpp b/src/boost/libs/yap/example/hello_world_redux.cpp
new file mode 100644
index 00000000..0bb7eac0
--- /dev/null
+++ b/src/boost/libs/yap/example/hello_world_redux.cpp
@@ -0,0 +1,32 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[hello_world_redux
+#include <boost/yap/algorithm.hpp>
+
+#include <iostream>
+
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct stream_expr
+{
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+
+    template <typename T>
+    decltype(auto) operator<< (T && x)
+    { return boost::yap::value(*this) << std::forward<T &&>(x); }
+};
+
+
+int main ()
+{
+    auto cout = boost::yap::make_terminal<stream_expr>(std::cout);
+    cout << "Hello" << ',' << " world!\n";
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/lazy_vector.cpp b/src/boost/libs/yap/example/lazy_vector.cpp
new file mode 100644
index 00000000..dd43ed84
--- /dev/null
+++ b/src/boost/libs/yap/example/lazy_vector.cpp
@@ -0,0 +1,112 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ lazy_vector
+#include <boost/yap/expression.hpp>
+
+#include <algorithm>
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr;
+
+
+// This transform turns a terminal of std::vector<double> into a terminal
+// containing the nth double in that vector.  Think of it as turning our
+// expression of vectors into an expression of scalars.
+struct take_nth
+{
+    boost::yap::terminal<lazy_vector_expr, double>
+    operator() (boost::yap::terminal<lazy_vector_expr, std::vector<double>> const & expr);
+
+    std::size_t n;
+};
+
+// A custom expression template that defines lazy + and - operators that
+// produce expressions, and an eager [] operator that returns the nth element
+// of the expression.
+//[ lazy_vector_decl
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr
+{
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+
+    // Note that this does not return an expression; it is greedily evaluated.
+    auto operator[] (std::size_t n) const;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, lazy_vector_expr, lazy_vector_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, lazy_vector_expr, lazy_vector_expr)
+//]
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+auto lazy_vector_expr<Kind, Tuple>::operator[] (std::size_t n) const
+{ return boost::yap::evaluate(boost::yap::transform(*this, take_nth{n})); }
+
+boost::yap::terminal<lazy_vector_expr, double>
+take_nth::operator() (boost::yap::terminal<lazy_vector_expr, std::vector<double>> const & expr)
+{
+    double x = boost::yap::value(expr)[n];
+    // This move is something of a hack; we're forcing Yap to take a copy of x
+    // by using std::move().  The move indicates that the terminal should keep
+    // the value of x (since, being an rvalue, it may be a temporary), rather
+    // than a reference to x.  See the "How Expression Operands Are Treated"
+    // section of the tutorial for details.
+    return boost::yap::make_terminal<lazy_vector_expr, double>(std::move(x));
+}
+
+// In order to define the += operator with the semantics we want, it's
+// convenient to derive a terminal type from a terminal instantiation of
+// lazy_vector_expr.  Note that we could have written a template
+// specialization here instead -- either one would work.  That would of course
+// have required more typing.
+struct lazy_vector :
+    lazy_vector_expr<
+        boost::yap::expr_kind::terminal,
+        boost::hana::tuple<std::vector<double>>
+    >
+{
+    lazy_vector () {}
+
+    explicit lazy_vector (std::vector<double> && vec)
+    { elements = boost::hana::tuple<std::vector<double>>(std::move(vec)); }
+
+    template <boost::yap::expr_kind Kind, typename Tuple>
+    lazy_vector & operator+= (lazy_vector_expr<Kind, Tuple> const & rhs)
+    {
+        std::vector<double> & this_vec = boost::yap::value(*this);
+        for (int i = 0, size = (int)this_vec.size(); i < size; ++i) {
+            this_vec[i] += rhs[i];
+        }
+        return *this;
+    }
+};
+
+int main ()
+{
+    lazy_vector v1{std::vector<double>(4, 1.0)};
+    lazy_vector v2{std::vector<double>(4, 2.0)};
+    lazy_vector v3{std::vector<double>(4, 3.0)};
+
+    double d1 = (v2 + v3)[2];
+    std::cout << d1 << "\n";
+
+    v1 += v2 - v3;
+    std::cout << '{' << v1[0] << ',' << v1[1]
+              << ',' << v1[2] << ',' << v1[3] << '}' << "\n";
+
+    // This expression is disallowed because it does not conform to the
+    // implicit grammar.  operator+= is only defined on terminals, not
+    // arbitrary expressions.
+    // (v2 + v3) += v1;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/let.cpp b/src/boost/libs/yap/example/let.cpp
new file mode 100644
index 00000000..0cac1975
--- /dev/null
+++ b/src/boost/libs/yap/example/let.cpp
@@ -0,0 +1,177 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ let
+#include <boost/yap/yap.hpp>
+
+#include <boost/hana/map.hpp>
+#include <boost/hana/at_key.hpp>
+#include <boost/hana/contains.hpp>
+#include <boost/hana/keys.hpp>
+
+#include <vector>
+#include <iostream>
+
+
+// Here, we introduce special let-placeholders, so we can use them along side
+// the normal YAP placeholders without getting them confused.
+template<long long I>
+struct let_placeholder : boost::hana::llong<I>
+{
+};
+
+// Replaces each let-terminal with the expression with which it was
+// initialized in let().  So in 'let(_a = foo)[ _a + 1 ]', this transform will
+// be used on '_a + 1' to replace '_a' with 'foo'.  The map_ member holds the
+// mapping of let-placeholders to their initializers.
+template<typename ExprMap>
+struct let_terminal_transform
+{
+    // This matches only let-placeholders.  For each one matched, we look up
+    // its initializer in map_ and return it.
+    template<long long I>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+        let_placeholder<I> i)
+    {
+        // If we have an entry in map_ for this placeholder, return the value
+        // of the entry.  Otherwise, pass i through as a terminal.
+        if constexpr (boost::hana::contains(
+                          decltype(boost::hana::keys(map_))(),
+                          boost::hana::llong_c<I>)) {
+            return map_[boost::hana::llong_c<I>];
+        } else {
+            return boost::yap::make_terminal(i);
+        }
+    }
+
+    ExprMap map_;
+};
+
+// As you can see below, let() is an eager function; this template is used for
+// its return values.  It contains the mapping from let-placeholders to
+// initializer expressions used to transform the expression inside '[]' after
+// a let()'.  It also has an operator[]() member function that takes the
+// expression inside '[]' and returns a version of it with the
+// let-placeholders replaced.
+template<typename ExprMap>
+struct let_result
+{
+    template<typename Expr>
+    auto operator[](Expr && expr)
+    {
+        return boost::yap::transform(
+            std::forward<Expr>(expr), let_terminal_transform<ExprMap>{map_});
+    }
+
+    ExprMap map_;
+};
+
+// Processes the expressions passed to let() one at a time, adding each one to
+// a Hana map of hana::llong<>s to YAP expressions.
+template<typename Map, typename Expr, typename... Exprs>
+auto let_impl(Map && map, Expr && expr, Exprs &&... exprs)
+{
+    static_assert(
+        Expr::kind == boost::yap::expr_kind::assign,
+        "Expressions passed to let() must be of the form placeholder = Expression");
+    if constexpr (sizeof...(Exprs) == 0) {
+        using I = typename std::remove_reference<decltype(
+            boost::yap::value(boost::yap::left(expr)))>::type;
+        auto const i = boost::hana::llong_c<I::value>;
+        using map_t = decltype(boost::hana::insert(
+            map, boost::hana::make_pair(i, boost::yap::right(expr))));
+        return let_result<map_t>{boost::hana::insert(
+            map, boost::hana::make_pair(i, boost::yap::right(expr)))};
+    } else {
+        using I = typename std::remove_reference<decltype(
+            boost::yap::value(boost::yap::left(expr)))>::type;
+        auto const i = boost::hana::llong_c<I::value>;
+        return let_impl(
+            boost::hana::insert(
+                map, boost::hana::make_pair(i, boost::yap::right(expr))),
+            std::forward<Exprs>(exprs)...);
+    }
+}
+
+// Takes N > 0 expressions of the form 'placeholder = expr', and returns an
+// object with an overloaded operator[]().
+template<typename Expr, typename... Exprs>
+auto let(Expr && expr, Exprs &&... exprs)
+{
+    return let_impl(
+        boost::hana::make_map(),
+        std::forward<Expr>(expr),
+        std::forward<Exprs>(exprs)...);
+}
+
+int main()
+{
+    // Some handy terminals -- the _a and _b let-placeholders and std::cout as
+    // a YAP terminal.
+    boost::yap::expression<
+        boost::yap::expr_kind::terminal,
+        boost::hana::tuple<let_placeholder<0>>> const _a;
+    boost::yap::expression<
+        boost::yap::expr_kind::terminal,
+        boost::hana::tuple<let_placeholder<1>>> const _b;
+    auto const cout = boost::yap::make_terminal(std::cout);
+
+    using namespace boost::yap::literals;
+
+    {
+        auto expr = let(_a = 2)[_a + 1];
+        assert(boost::yap::evaluate(expr) == 3);
+    }
+
+    {
+        auto expr = let(_a = 123, _b = 456)[_a + _b];
+        assert(boost::yap::evaluate(expr) == 123 + 456);
+    }
+
+    // This prints out "0 0", because 'i' is passed as an lvalue, so its
+    // decrement is visible outside the let expression.
+    {
+        int i = 1;
+
+        boost::yap::evaluate(let(_a = 1_p)[cout << --_a << ' '], i);
+
+        std::cout << i << std::endl;
+    }
+
+    // Prints "Hello, World" due to let()'s scoping rules.
+    {
+        boost::yap::evaluate(
+            let(_a = 1_p, _b = 2_p)
+            [
+                // _a here is an int: 1
+
+                let(_a = 3_p) // hides the outer _a
+                [
+                    cout << _a << _b // prints "Hello, World"
+                ]
+            ],
+            1, " World", "Hello,"
+        );
+    }
+
+    std::cout << "\n";
+
+    // Due to the macro-substitution style that this example uses, this prints
+    // "3132".  Phoenix's let() prints "312", because it only evaluates '1_p
+    // << 3' once.
+    {
+        boost::yap::evaluate(
+            let(_a = 1_p << 3)
+            [
+                _a << "1", _a << "2"
+            ],
+            std::cout
+        );
+    }
+
+    std::cout << "\n";
+}
+//]
diff --git a/src/boost/libs/yap/example/map_assign.cpp b/src/boost/libs/yap/example/map_assign.cpp
new file mode 100644
index 00000000..d8b304be
--- /dev/null
+++ b/src/boost/libs/yap/example/map_assign.cpp
@@ -0,0 +1,93 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ map_assign
+#include <boost/yap/algorithm.hpp>
+
+#include <map>
+#include <iostream>
+
+
+// This transform applies all the call-subexpressions in a map_list_of
+// expression (a nested chain of call operations) as a side effect; the
+// expression returned by the transform is ignored.
+template <typename Key, typename Value, typename Allocator>
+struct map_list_of_transform
+{
+    template <typename Fn, typename Key2, typename Value2>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::call>,
+                     Fn const & fn, Key2 && key, Value2 && value)
+    {
+        // Recurse into the function subexpression.  Remember, transform()
+        // walks the nodes in an expression tree looking for matches.  Once it
+        // finds a match, it is finished with that matching subtree.  So
+        // without this recursive call, only the top-level call expression is
+        // matched by transform().
+        boost::yap::transform(
+            boost::yap::as_expr<boost::yap::minimal_expr>(fn), *this);
+        map.emplace(
+            std::forward<Key2 &&>(key),
+            std::forward<Value2 &&>(value)
+        );
+        // All we care about are the side effects of this transform, so we can
+        // return any old thing here.
+        return 0;
+    }
+
+    std::map<Key, Value, Allocator> & map;
+};
+
+
+// A custom expression template type for map_list_of expressions.  We only
+// need support for the call operator and an implicit conversion to a
+// std::map.
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct map_list_of_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+
+    template <typename Key, typename Value, typename Allocator>
+    operator std::map<Key, Value, Allocator> () const
+    {
+        std::map<Key, Value, Allocator> retval;
+        map_list_of_transform<Key, Value, Allocator> transform{retval};
+        boost::yap::transform(*this, transform);
+        return retval;
+    }
+
+    BOOST_YAP_USER_CALL_OPERATOR_N(::map_list_of_expr, 2)
+};
+
+// A tag type for creating the map_list_of function terminal.
+struct map_list_of_tag {};
+
+auto map_list_of = boost::yap::make_terminal<map_list_of_expr>(map_list_of_tag{});
+
+
+int main()
+{
+    // Initialize a map:
+    std::map<std::string, int> op =
+        map_list_of
+            ("<", 1)
+            ("<=",2)
+            (">", 3)
+            (">=",4)
+            ("=", 5)
+            ("<>",6)
+        ;
+
+    std::cout << "\"<\"  --> " << op["<"] << std::endl;
+    std::cout << "\"<=\" --> " << op["<="] << std::endl;
+    std::cout << "\">\"  --> " << op[">"] << std::endl;
+    std::cout << "\">=\" --> " << op[">="] << std::endl;
+    std::cout << "\"=\"  --> " << op["="] << std::endl;
+    std::cout << "\"<>\" --> " << op["<>"] << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/minimal.cpp b/src/boost/libs/yap/example/minimal.cpp
new file mode 100644
index 00000000..d79e372f
--- /dev/null
+++ b/src/boost/libs/yap/example/minimal.cpp
@@ -0,0 +1,42 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/algorithm.hpp>
+
+#include <array>
+#include <iostream>
+
+
+//[ minimal_template
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct minimal_expr
+{
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+};
+//]
+
+
+int main()
+{
+//[ minimal_template_manual_construction
+    auto left = boost::yap::make_terminal<minimal_expr>(1);
+    auto right = boost::yap::make_terminal<minimal_expr>(41);
+
+    auto expr = boost::yap::make_expression<
+        minimal_expr,
+        boost::yap::expr_kind::plus
+    >(left, right);
+//]
+
+//[ minimal_template_evaluation
+    auto result = boost::yap::evaluate(expr);
+
+    std::cout << result << "\n"; // prints "42"
+//]
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/example/mixed.cpp b/src/boost/libs/yap/example/mixed.cpp
new file mode 100644
index 00000000..e7dee54c
--- /dev/null
+++ b/src/boost/libs/yap/example/mixed.cpp
@@ -0,0 +1,213 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ mixed
+#include <boost/yap/yap.hpp>
+
+#include <complex>
+#include <list>
+#include <vector>
+#include <iostream>
+
+
+// This wrapper makes the pattern matching in transforms below (like deref and
+// incr) a lot easier to write.
+template <typename Iter>
+struct iter_wrapper
+{
+    Iter it;
+};
+
+template <typename Iter>
+auto make_iter_wrapper (Iter it)
+{ return iter_wrapper<Iter>{it}; }
+
+
+// A container -> wrapped-begin transform.
+struct begin
+{
+    template <typename Cont>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                     Cont const & cont)
+        -> decltype(boost::yap::make_terminal(make_iter_wrapper(cont.begin())))
+    { return boost::yap::make_terminal(make_iter_wrapper(cont.begin())); }
+};
+
+// A wrapped-iterator -> dereferenced value transform.
+struct deref
+{
+    template <typename Iter>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                     iter_wrapper<Iter> wrapper)
+        -> decltype(boost::yap::make_terminal(*wrapper.it))
+    { return boost::yap::make_terminal(*wrapper.it); }
+};
+
+// A wrapped-iterator increment transform, using side effects.
+struct incr
+{
+    template <typename Iter>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                     iter_wrapper<Iter> & wrapper)
+        -> decltype(boost::yap::make_terminal(wrapper.it))
+    {
+        ++wrapper.it;
+        // Since this transform is valuable for its side effects, and thus the
+        // result of the transform is ignored, we could return anything here.
+        return boost::yap::make_terminal(wrapper.it);
+    }
+};
+
+
+// The implementation of elementwise evaluation of expressions of sequences;
+// all the later operations use this one.
+template <
+    template <class, class> class Cont,
+    typename T,
+    typename A,
+    typename Expr,
+    typename Op
+>
+Cont<T, A> & op_assign (Cont<T, A> & cont, Expr const & e, Op && op)
+{
+    decltype(auto) expr = boost::yap::as_expr(e);
+    // Transform the expression of sequences into an expression of
+    // begin-iterators.
+    auto expr2 = boost::yap::transform(boost::yap::as_expr(expr), begin{});
+    for (auto && x : cont) {
+        // Transform the expression of iterators into an expression of
+        // pointed-to-values, evaluate the resulting expression, and call op()
+        // with the result of the evaluation.
+        op(x, boost::yap::evaluate(boost::yap::transform(expr2, deref{})));
+        // Transform the expression of iterators into an ignored value; as a
+        // side effect, increment the iterators in the expression.
+        boost::yap::transform(expr2, incr{});
+    }
+    return cont;
+}
+
+template <
+    template <class, class> class Cont,
+    typename T,
+    typename A,
+    typename Expr
+>
+Cont<T, A> & assign (Cont<T, A> & cont, Expr const & expr)
+{
+    return op_assign(cont, expr, [](auto & cont_value, auto && expr_value) {
+        cont_value = std::forward<decltype(expr_value)>(expr_value);
+    });
+}
+
+template <
+    template <class, class> class Cont,
+    typename T,
+    typename A,
+    typename Expr
+>
+Cont<T, A> & operator+= (Cont<T, A> & cont, Expr const & expr)
+{
+    return op_assign(cont, expr, [](auto & cont_value, auto && expr_value) {
+        cont_value += std::forward<decltype(expr_value)>(expr_value);
+    });
+}
+
+template <
+    template <class, class> class Cont,
+    typename T,
+    typename A,
+    typename Expr
+>
+Cont<T, A> & operator-= (Cont<T, A> & cont, Expr const & expr)
+{
+    return op_assign(cont, expr, [](auto & cont_value, auto && expr_value) {
+        cont_value -= std::forward<decltype(expr_value)>(expr_value);
+    });
+}
+
+// A type trait that identifies std::vectors and std::lists.
+template <typename T>
+struct is_mixed : std::false_type {};
+
+template <typename T, typename A>
+struct is_mixed<std::vector<T, A>> : std::true_type {};
+
+template <typename T, typename A>
+struct is_mixed<std::list<T, A>> : std::true_type {};
+
+// Define expression-producing operators over std::vectors and std::lists.
+BOOST_YAP_USER_UDT_UNARY_OPERATOR(negate, boost::yap::expression, is_mixed); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(multiplies, boost::yap::expression, is_mixed); // *
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(divides, boost::yap::expression, is_mixed); // /
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(modulus, boost::yap::expression, is_mixed); // %
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(plus, boost::yap::expression, is_mixed); // +
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(minus, boost::yap::expression, is_mixed); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(less, boost::yap::expression, is_mixed); // <
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(greater, boost::yap::expression, is_mixed); // >
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(less_equal, boost::yap::expression, is_mixed); // <=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(greater_equal, boost::yap::expression, is_mixed); // >=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(equal_to, boost::yap::expression, is_mixed); // ==
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(not_equal_to, boost::yap::expression, is_mixed); // !=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(logical_or, boost::yap::expression, is_mixed); // ||
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(logical_and, boost::yap::expression, is_mixed); // &&
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_and, boost::yap::expression, is_mixed); // &
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_or, boost::yap::expression, is_mixed); // |
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_xor, boost::yap::expression, is_mixed); // ^
+
+// Define a type that can resolve to any overload of std::sin().
+struct sin_t
+{
+    template<typename T>
+    T operator()(T x)
+    {
+        return std::sin(x);
+    }
+};
+
+int main()
+{
+    int n = 10;
+    std::vector<int> a,b,c,d;
+    std::list<double> e;
+    std::list<std::complex<double>> f;
+
+    int i;
+    for(i = 0;i < n; ++i)
+    {
+        a.push_back(i);
+        b.push_back(2*i);
+        c.push_back(3*i);
+        d.push_back(i);
+        e.push_back(0.0);
+        f.push_back(std::complex<double>(1.0, 1.0));
+    }
+
+    assign(b, 2);
+    assign(d, a + b * c);
+    a += if_else(d < 30, b, c);
+
+    assign(e, c);
+    e += e - 4 / (c + 1);
+
+    auto sin = boost::yap::make_terminal(sin_t{});
+    f -= sin(0.1 * e * std::complex<double>(0.2, 1.2));
+
+    std::list<double>::const_iterator ei = e.begin();
+    std::list<std::complex<double>>::const_iterator fi = f.begin();
+    for (i = 0; i < n; ++i)
+    {
+        std::cout
+            << "a(" << i << ") = " << a[i]
+            << " b(" << i << ") = " << b[i]
+            << " c(" << i << ") = " << c[i]
+            << " d(" << i << ") = " << d[i]
+            << " e(" << i << ") = " << *ei++
+            << " f(" << i << ") = " << *fi++
+            << std::endl;
+    }
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/pipable_algorithms.cpp b/src/boost/libs/yap/example/pipable_algorithms.cpp
new file mode 100644
index 00000000..07c71f54
--- /dev/null
+++ b/src/boost/libs/yap/example/pipable_algorithms.cpp
@@ -0,0 +1,147 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ pipable_algorithms
+#include <boost/yap/algorithm.hpp>
+
+#include <algorithm>
+#include <vector>
+
+
+//[ pipable_algorithms_and_simple_range
+// An enum to represent all the standard algorithms we want to adapt.  In this
+// example, we only care about std::sort() and std::unique().
+enum class algorithm_t { sort, unique };
+
+// Just about the simplest range template you could construct.  Nothing fancy.
+template<typename Iter>
+struct simple_range
+{
+    Iter begin() const { return first_; }
+    Iter end() const { return last_; }
+
+    Iter first_;
+    Iter last_;
+};
+
+// This simply calls the standard algorithm that corresponds to "a".  This
+// certainly won't work for all the algorithms, but it works for many of them
+// that just take a begin/end pair.
+template<typename Range>
+auto call_algorithm(algorithm_t a, Range & r)
+{
+    simple_range<decltype(r.begin())> retval{r.begin(), r.end()};
+    if (a == algorithm_t::sort) {
+        std::sort(r.begin(), r.end());
+    } else if (a == algorithm_t::unique) {
+        retval.last_ = std::unique(r.begin(), r.end());
+    }
+    return retval;
+}
+//]
+
+// This is the transform that evaluates our piped expressions.  It returns a
+// simple_range<>, not a Yap expression.
+struct algorithm_eval
+{
+    // A pipe should always have a Yap expression on the left and an
+    // algorithm_t terminal on the right.
+    template<typename LExpr>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::bitwise_or>,
+        LExpr && left,
+        algorithm_t right)
+    {
+        // Recursively evaluate the left ...
+        auto const left_result =
+            boost::yap::transform(std::forward<LExpr>(left), *this);
+        // ... and use the result to call the function on the right.
+        return call_algorithm(right, left_result);
+    }
+
+    // A call operation is evaluated directly.  Note that the range parameter
+    // is taken as an lvalue reference, to prevent binding to a temporary and
+    // taking dangling references to its begin and end.  We let the compiler
+    // deduce whether the lvalue reference is const.
+//[ tag_xform
+    template<typename Range>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::call>,
+        algorithm_t a,
+        Range & r)
+    {
+        return call_algorithm(a, r);
+    }
+//]
+};
+
+// This is the expression template we use for the general case of a pipable
+// algorithm expression.  Terminals are handled separately.
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct algorithm_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+
+    // This is how we get the nice initializer semantics we see in the example
+    // usage below.  This is a bit limited though, because we always create a
+    // temporary.  It might therefore be better just to create algorithm_expr
+    // expressions, call yap::evaluate(), and then use the sequence containers
+    // assign() member function to do the actual assignment.
+    template<typename Assignee>
+    operator Assignee() const
+    {
+        // Exercise left for the reader: static_assert() that Assignee is some
+        // sort of container type.
+        auto const range = boost::yap::transform(*this, algorithm_eval{});
+        return Assignee(range.begin(), range.end());
+    }
+};
+
+
+// This is a bit loose, because it allows us to write "sort(v) | unique(u)" or
+// similar.  It works fine for this example, but in production code you may
+// want to write out the functions generated by this macro, and add SFINAE or
+// concepts constraints on the right template parameter.
+BOOST_YAP_USER_BINARY_OPERATOR(bitwise_or, algorithm_expr, algorithm_expr)
+
+// It's useful to specially handle terminals, because we want a different set
+// of operations to apply to them.  We don't want "sort(x)(y)" to be
+// well-formed, for instance, or "sort | unique" either.
+struct algorithm
+{
+    static boost::yap::expr_kind const kind = boost::yap::expr_kind::terminal;
+
+    boost::hana::tuple<algorithm_t> elements;
+
+    BOOST_YAP_USER_CALL_OPERATOR_N(::algorithm_expr, 1)
+};
+
+// Here are ready-made Yap terminals, one for each algorithm enumerated in
+// algorithm_t.
+constexpr algorithm sort{{algorithm_t::sort}};
+constexpr algorithm unique{{algorithm_t::unique}};
+
+int main()
+{
+    {
+//[ typical_sort_unique_usage
+        std::vector<int> v1 = {0, 2, 2, 7, 1, 3, 8};
+        std::sort(v1.begin(), v1.end());
+        auto it = std::unique(v1.begin(), v1.end());
+        std::vector<int> const v2(v1.begin(), it);
+        assert(v2 == std::vector<int>({0, 1, 2, 3, 7, 8}));
+//]
+    }
+    {
+//[ pipable_sort_unique_usage
+        std::vector<int> v1 = {0, 2, 2, 7, 1, 3, 8};
+        std::vector<int> const v2 = sort(v1) | unique;
+        assert(v2 == std::vector<int>({0, 1, 2, 3, 7, 8}));
+//]
+    }
+}
+//]
diff --git a/src/boost/libs/yap/example/self_evaluation.cpp b/src/boost/libs/yap/example/self_evaluation.cpp
new file mode 100644
index 00000000..d5c7323d
--- /dev/null
+++ b/src/boost/libs/yap/example/self_evaluation.cpp
@@ -0,0 +1,237 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ self_evaluation
+#include <boost/yap/expression.hpp>
+
+#include <boost/optional.hpp>
+#include <boost/hana/fold.hpp>
+#include <boost/hana/maximum.hpp>
+
+#include <algorithm>
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+
+// A super-basic matrix type, and a few associated operations.
+struct matrix
+{
+    matrix() : values_(), rows_(0), cols_(0) {}
+
+    matrix(int rows, int cols) : values_(rows * cols), rows_(rows), cols_(cols)
+    {
+        assert(0 < rows);
+        assert(0 < cols);
+    }
+
+    int rows() const { return rows_; }
+    int cols() const { return cols_; }
+
+    double operator()(int r, int c) const
+    { return values_[r * cols_ + c]; }
+    double & operator()(int r, int c)
+    { return values_[r * cols_ + c]; }
+
+private:
+    std::vector<double> values_;
+    int rows_;
+    int cols_;
+};
+
+matrix operator*(matrix const & lhs, double x)
+{
+    matrix retval = lhs;
+    for (int i = 0; i < retval.rows(); ++i) {
+        for (int j = 0; j < retval.cols(); ++j) {
+            retval(i, j) *= x;
+        }
+    }
+    return retval;
+}
+matrix operator*(double x, matrix const & lhs) { return lhs * x; }
+
+matrix operator+(matrix const & lhs, matrix const & rhs)
+{
+    assert(lhs.rows() == rhs.rows());
+    assert(lhs.cols() == rhs.cols());
+    matrix retval = lhs;
+    for (int i = 0; i < retval.rows(); ++i) {
+        for (int j = 0; j < retval.cols(); ++j) {
+            retval(i, j) += rhs(i, j);
+        }
+    }
+    return retval;
+}
+
+// daxpy() means Double-precision AX Plus Y.  This crazy name comes from BLAS.
+// It is more efficient than a naive implementation, because it does not
+// create temporaries.  The covnention of using Y as an out-parameter comes
+// from FORTRAN BLAS.
+matrix & daxpy(double a, matrix const & x, matrix & y)
+{
+    assert(x.rows() == y.rows());
+    assert(x.cols() == y.cols());
+    for (int i = 0; i < y.rows(); ++i) {
+        for (int j = 0; j < y.cols(); ++j) {
+            y(i, j) += a * x(i, j);
+        }
+    }
+    return y;
+}
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct self_evaluating_expr;
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+auto evaluate_matrix_expr(self_evaluating_expr<Kind, Tuple> const & expr);
+
+// This is the primary template for our expression template.  If you assign a
+// self_evaluating_expr to a matrix, its conversion operator transforms and
+// evaluates the expression with a call to evaluate_matrix_expr().
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct self_evaluating_expr
+{
+    operator auto() const;
+
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+};
+
+// This is a specialization of our expression template for assignment
+// expressions.  The destructor transforms and evaluates via a call to
+// evaluate_matrix_expr(), and then assigns the result to the variable on the
+// left side of the assignment.
+//
+// In a production implementation, you'd need to have specializations for
+// plus_assign, minus_assign, etc.
+template <typename Tuple>
+struct self_evaluating_expr<boost::yap::expr_kind::assign, Tuple>
+{
+    ~self_evaluating_expr();
+
+    static const boost::yap::expr_kind kind = boost::yap::expr_kind::assign;
+
+    Tuple elements;
+};
+
+struct use_daxpy
+{
+    // A plus-expression, which may be of the form double * matrix + matrix,
+    // or may be something else.  Since our daxpy() above requires a mutable
+    // "y", we only need to match a mutable lvalue matrix reference here.
+    template <typename Tuple>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::plus>,
+        self_evaluating_expr<boost::yap::expr_kind::multiplies, Tuple> const & expr,
+        matrix & m)
+    {
+        // Here, we transform the left-hand side into a pair if it's the
+        // double * matrix operation we're looking for.  Otherwise, we just
+        // get a copy of the left side expression.
+        //
+        // Note that this is a bit of a cheat, done for clarity.  If we pass a
+        // larger expression that happens to contain a double * matrix
+        // subexpression, that subexpression will be transformed into a tuple!
+        // In production code, this transform should probably only be
+        // performed on an expression with all terminal members.
+        auto lhs = boost::yap::transform(
+            expr,
+            [](boost::yap::expr_tag<boost::yap::expr_kind::multiplies>,
+               double d,
+               matrix const & m) {
+                return std::pair<double, matrix const &>(d, m);
+            });
+
+        // If we got back a copy of expr above, just re-construct the
+        // expression this function mathes; in other words, do not effectively
+        // transform anything.  Otherwise, replace the expression matched by
+        // this function with a call to daxpy().
+        if constexpr (boost::yap::is_expr<decltype(lhs)>::value) {
+            return expr + m;
+        } else {
+            return boost::yap::make_terminal(daxpy)(lhs.first, lhs.second, m);
+        }
+    }
+};
+
+
+// This is the heart of what self_evaluating_expr does.  If we had other
+// optimizations/transformations we wanted to do, we'd put them in this
+// function, either before or after the use_daxpy transformation.
+template <boost::yap::expr_kind Kind, typename Tuple>
+auto evaluate_matrix_expr(self_evaluating_expr<Kind, Tuple> const & expr)
+{
+    auto daxpy_form = boost::yap::transform(expr, use_daxpy{});
+    return boost::yap::evaluate(daxpy_form);
+}
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+self_evaluating_expr<Kind, Tuple>::operator auto() const
+{
+    return evaluate_matrix_expr(*this);
+}
+
+template<typename Tuple>
+self_evaluating_expr<boost::yap::expr_kind::assign, Tuple>::
+    ~self_evaluating_expr()
+{
+    using namespace boost::hana::literals;
+    boost::yap::evaluate(elements[0_c]) = evaluate_matrix_expr(elements[1_c]);
+}
+
+// In order to define the = operator with the semantics we want, it's
+// convenient to derive a terminal type from a terminal instantiation of
+// self_evaluating_expr.  Note that we could have written a template
+// specialization here instead -- either one would work.  That would of course
+// have required more typing.
+struct self_evaluating :
+    self_evaluating_expr<
+        boost::yap::expr_kind::terminal,
+        boost::hana::tuple<matrix>
+    >
+{
+    self_evaluating() {}
+
+    explicit self_evaluating(matrix m)
+    { elements = boost::hana::tuple<matrix>(std::move(m)); }
+
+    BOOST_YAP_USER_ASSIGN_OPERATOR(self_evaluating_expr, ::self_evaluating_expr);
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, self_evaluating_expr, self_evaluating_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, self_evaluating_expr, self_evaluating_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(multiplies, self_evaluating_expr, self_evaluating_expr)
+
+
+int main()
+{
+    matrix identity(2, 2);
+    identity(0, 0) = 1.0;
+    identity(1, 1) = 1.0;
+
+    // These are YAP-ified terminal expressions.
+    self_evaluating m1(identity);
+    self_evaluating m2(identity);
+    self_evaluating m3(identity);
+
+    // This transforms the YAP expression to use daxpy(), so it creates no
+    // temporaries.  The transform happens in the destructor of the
+    // assignment-expression specialization of self_evaluating_expr.
+    m1 = 3.0 * m2 + m3;
+
+    // Same as above, except that it uses the matrix conversion operator on
+    // the self_evaluating_expr primary template, because here we're assigning
+    // a YAP expression to a non-YAP-ified matrix.
+    matrix m_result_1 = 3.0 * m2 + m3;
+
+    // Creates temporaries and does not use daxpy(), because the A * X + Y
+    // pattern does not occur within the expression.
+    matrix m_result_2 = 3.0 * m2;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/tarray.cpp b/src/boost/libs/yap/example/tarray.cpp
new file mode 100644
index 00000000..6aa4e109
--- /dev/null
+++ b/src/boost/libs/yap/example/tarray.cpp
@@ -0,0 +1,186 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ tarray
+#include <boost/yap/algorithm.hpp>
+#include <boost/yap/print.hpp>
+
+#include <array>
+#include <iostream>
+
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct tarray_expr;
+
+
+struct take_nth
+{
+    boost::yap::terminal<tarray_expr, int>
+    operator() (boost::yap::terminal<tarray_expr, std::array<int, 3>> const & expr);
+
+    std::size_t n;
+};
+
+// Another custom expression template.  In this case, we static_assert() that
+// it only gets instantiated with terminals with pre-approved value types.
+template <boost::yap::expr_kind Kind, typename Tuple>
+struct tarray_expr
+{
+    // Make sure that, if this expression is a terminal, its value is one we
+    // want to support.  Note that the presence of expr_kind::expr_ref makes
+    // life slightly more difficult; we have to account for int const & and
+    // int & as well as int.
+    static_assert(
+        Kind != boost::yap::expr_kind::terminal ||
+        std::is_same<Tuple, boost::hana::tuple<int const &>>{} ||
+        std::is_same<Tuple, boost::hana::tuple<int &>>{} ||
+        std::is_same<Tuple, boost::hana::tuple<int>>{} ||
+        std::is_same<Tuple, boost::hana::tuple<std::array<int, 3>>>{},
+        "tarray_expr instantiated with an unsupported terminal type."
+    );
+
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+
+    int operator[] (std::size_t n) const
+    { return boost::yap::evaluate(boost::yap::transform(*this, take_nth{n})); }
+};
+
+// Define operators +, -, *, and /.
+BOOST_YAP_USER_BINARY_OPERATOR(plus, tarray_expr, tarray_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, tarray_expr, tarray_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(multiplies, tarray_expr, tarray_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(divides, tarray_expr, tarray_expr)
+
+
+boost::yap::terminal<tarray_expr, int>
+take_nth::operator() (boost::yap::terminal<tarray_expr, std::array<int, 3>> const & expr)
+{
+    int x = boost::yap::value(expr)[n];
+    // Again, this is the move hack to get x into the resulting terminal as a
+    // value instead of a reference.
+    return boost::yap::make_terminal<tarray_expr>(std::move(x));
+}
+
+
+// Stream-out operators for the two kinds of terminals we support.
+
+std::ostream & operator<< (std::ostream & os, boost::yap::terminal<tarray_expr, int> expr)
+{ return os << '{' << boost::yap::value(expr) << '}'; }
+
+std::ostream & operator<< (std::ostream & os, boost::yap::terminal<tarray_expr, std::array<int, 3>> expr)
+{
+    std::array<int, 3> const & a = boost::yap::value(expr);
+    return os << '{' << a[0] << ", " << a[1] << ", " << a[2] << '}';
+}
+
+// Stream-out operators for general expressions.  Note that we have to treat
+// the reference case separately; this also could have been done using
+// constexpr if in a single function template.
+
+template <typename Tuple>
+std::ostream & operator<< (std::ostream & os, tarray_expr<boost::yap::expr_kind::expr_ref, Tuple> const & expr)
+{ return os << boost::yap::deref(expr); }
+
+template <boost::yap::expr_kind Kind, typename Tuple>
+std::ostream & operator<< (std::ostream & os, tarray_expr<Kind, Tuple> const & expr)
+{
+    if (Kind == boost::yap::expr_kind::plus || Kind == boost::yap::expr_kind::minus)
+        os << '(';
+    os << boost::yap::left(expr) << " " << op_string(Kind) << " " << boost::yap::right(expr);
+    if (Kind == boost::yap::expr_kind::plus || Kind == boost::yap::expr_kind::minus)
+        os << ')';
+    return os;
+}
+
+
+// Since we want different behavior on terminals than on other kinds of
+// expressions, we create a custom type that does so.
+struct tarray :
+    tarray_expr<
+        boost::yap::expr_kind::terminal,
+        boost::hana::tuple<std::array<int, 3>>
+    >
+{
+    explicit tarray (int i = 0, int j = 0, int k = 0)
+    {
+        (*this)[0] = i;
+        (*this)[1] = j;
+        (*this)[2] = k;
+    }
+
+    explicit tarray (std::array<int, 3> a)
+    {
+        (*this)[0] = a[0];
+        (*this)[1] = a[1];
+        (*this)[2] = a[2];
+    }
+
+    int & operator[] (std::ptrdiff_t i)
+    { return boost::yap::value(*this)[i]; }
+
+    int const & operator[] (std::ptrdiff_t i) const
+    { return boost::yap::value(*this)[i]; }
+
+    template <typename T>
+    tarray & operator= (T const & t)
+    {
+        // We use as_expr() here to make sure that the value passed to
+        // assign() is an expression.  as_expr() simply forwards expressions
+        // through, and wraps non-expressions as terminals.
+        return assign(boost::yap::as_expr< ::tarray_expr>(t));
+    }
+
+    template <typename Expr>
+    tarray & printAssign (Expr const & expr)
+    {
+        *this = expr;
+        std::cout << *this << " = " << expr << std::endl;
+        return *this;
+    }
+
+private:
+    template <typename Expr>
+    tarray & assign (Expr const & expr)
+    {
+        (*this)[0] = expr[0];
+        (*this)[1] = expr[1];
+        (*this)[2] = expr[2];
+        return *this;
+    }
+};
+
+
+int main()
+{
+    tarray a(3,1,2);
+
+    tarray b;
+
+    std::cout << a << std::endl;
+    std::cout << b << std::endl;
+
+    b[0] = 7; b[1] = 33; b[2] = -99;
+
+    tarray c(a);
+
+    std::cout << c << std::endl;
+
+    a = 0;
+
+    std::cout << a << std::endl;
+    std::cout << b << std::endl;
+    std::cout << c << std::endl;
+
+    a = b + c;
+
+    std::cout << a << std::endl;
+
+    a.printAssign(b+c*(b + 3*c));
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/transform_terminals.cpp b/src/boost/libs/yap/example/transform_terminals.cpp
new file mode 100644
index 00000000..2bab93d6
--- /dev/null
+++ b/src/boost/libs/yap/example/transform_terminals.cpp
@@ -0,0 +1,72 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ transform_terminals
+#include <boost/yap/yap.hpp>
+
+
+struct iota_terminal_transform
+{
+    // Base case. Note that we're not treating placeholders specially for this
+    // example (they're easy to special-case if necessary).
+    template<typename T>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T && t)
+    {
+        // Like the std::iota() algorithm, we create replacement int terminals
+        // with the values index_, index_ + 1, index_ + 2, etc.
+        return boost::yap::make_terminal(index_++);
+    }
+
+    // Recursive case: Match any call expression.
+    template<typename CallableExpr, typename... Arg>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::call>,
+                    CallableExpr callable, Arg &&... arg)
+    {
+        // Even though the callable in a call expression is technically a
+        // terminal, it doesn't make a lot of sense to replace it with an int,
+        // so we'll only transform the argument subexpressions.
+        return boost::yap::make_expression<boost::yap::expr_kind::call>(
+            boost::yap::as_expr(callable),
+            boost::yap::transform(boost::yap::as_expr(arg), *this)...);
+    }
+
+    int index_;
+};
+
+int sum(int a, int b) { return a + b; }
+
+int main()
+{
+    {
+        // This simple sum(8, 8) expression requires both overloads of
+        // iota_terminal_transform.
+        auto expr = boost::yap::make_terminal(sum)(8, 8);
+        assert(evaluate(expr) == 16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{1});
+        assert(evaluate(iota_expr) == 3);
+    }
+
+    {
+        // This expression requires only the terminal case of
+        // iota_terminal_transform.
+        auto expr = -(boost::yap::make_terminal(8) + 8);
+        assert(evaluate(expr) == -16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
+        assert(evaluate(iota_expr) == -1);
+    }
+
+    {
+        // Like the first expression above, this expression requires both
+        // overloads of iota_terminal_transform.
+        auto expr = boost::yap::make_terminal(sum)(-(boost::yap::make_terminal(8) + 8), 0);
+        assert(evaluate(expr) == -16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
+        assert(evaluate(iota_expr) == -3);
+    }
+}
+//]
diff --git a/src/boost/libs/yap/example/vec3.cpp b/src/boost/libs/yap/example/vec3.cpp
new file mode 100644
index 00000000..5a458dda
--- /dev/null
+++ b/src/boost/libs/yap/example/vec3.cpp
@@ -0,0 +1,129 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ vec3
+#include <boost/yap/yap.hpp>
+
+#include <array>
+#include <iostream>
+
+
+struct take_nth
+{
+    auto operator() (boost::yap::terminal<boost::yap::expression, std::array<int, 3>> const & expr)
+    {
+        int x = boost::yap::value(expr)[n];
+        // The move forces the terminal to store the value of x, not a
+        // reference.
+        return boost::yap::make_terminal(std::move(x));
+    }
+
+    std::size_t n;
+};
+
+// Since this example doesn't constrain the operators defined on its
+// expressions, we can just use boost::yap::expression<> as the expression
+// template.
+using vec3_terminal = boost::yap::expression<
+    boost::yap::expr_kind::terminal,
+    boost::hana::tuple<std::array<int, 3>>
+>;
+
+// Customize the terminal type we use by adding index and assignment
+// operations.
+struct vec3 : vec3_terminal
+{
+    explicit vec3 (int i = 0, int j = 0, int k = 0)
+    {
+        (*this)[0] = i;
+        (*this)[1] = j;
+        (*this)[2] = k;
+    }
+
+    explicit vec3 (std::array<int, 3> a)
+    {
+        (*this)[0] = a[0];
+        (*this)[1] = a[1];
+        (*this)[2] = a[2];
+    }
+
+    int & operator[] (std::ptrdiff_t i)
+    { return boost::yap::value(*this)[i]; }
+
+    int const & operator[] (std::ptrdiff_t i) const
+    { return boost::yap::value(*this)[i]; }
+
+    template <typename T>
+    vec3 & operator= (T const & t)
+    {
+        decltype(auto) expr = boost::yap::as_expr(t);
+        (*this)[0] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{0}));
+        (*this)[1] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{1}));
+        (*this)[2] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{2}));
+        return *this;
+    }
+
+    void print() const
+    {
+        std::cout << '{' << (*this)[0]
+                  << ", " << (*this)[1]
+                  << ", " << (*this)[2]
+                  << '}' << std::endl;
+    }
+};
+
+// This is a stateful transform that keeps a running count of the terminals it
+// has seen.
+struct count_leaves_impl
+{
+    auto operator() (vec3_terminal const & expr)
+    {
+        value += 1;
+        return expr;
+    }
+
+    int value = 0;
+};
+
+template <typename Expr>
+int count_leaves (Expr const & expr)
+{
+    count_leaves_impl impl;
+    boost::yap::transform(boost::yap::as_expr(expr), impl);
+    return impl.value;
+}
+
+
+int main()
+{
+    vec3 a, b, c;
+
+    c = 4;
+
+    b[0] = -1;
+    b[1] = -2;
+    b[2] = -3;
+
+    a = b + c;
+
+    a.print();
+
+    vec3 d;
+    auto expr1 = b + c;
+    d = expr1;
+    d.print();
+
+    int num = count_leaves(expr1);
+    std::cout << num << std::endl;
+
+    num = count_leaves(b + 3 * c);
+    std::cout << num << std::endl;
+
+    num = count_leaves(b + c * d);
+    std::cout << num << std::endl;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/example/vector.cpp b/src/boost/libs/yap/example/vector.cpp
new file mode 100644
index 00000000..e6bd185b
--- /dev/null
+++ b/src/boost/libs/yap/example/vector.cpp
@@ -0,0 +1,145 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ vector
+#include <boost/yap/yap.hpp>
+
+#include <vector>
+#include <iostream>
+
+
+//[ vector_take_nth_xform
+struct take_nth
+{
+    template <typename T>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                     std::vector<T> const & vec)
+    { return boost::yap::make_terminal(vec[n]); }
+
+    std::size_t n;
+};
+//]
+
+// A stateful transform that records whether all the std::vector<> terminals
+// it has seen are equal to the given size.
+struct equal_sizes_impl
+{
+    template <typename T>
+    auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+                     std::vector<T> const & vec)
+    {
+        auto const expr_size = vec.size();
+        if (expr_size != size)
+            value = false;
+        return 0;
+    }
+
+    std::size_t const size;
+    bool value;
+};
+
+template <typename Expr>
+bool equal_sizes (std::size_t size, Expr const & expr)
+{
+    equal_sizes_impl impl{size, true};
+    boost::yap::transform(boost::yap::as_expr(expr), impl);
+    return impl.value;
+}
+
+
+// Assigns some expression e to the given vector by evaluating e elementwise,
+// to avoid temporaries and allocations.
+template <typename T, typename Expr>
+std::vector<T> & assign (std::vector<T> & vec, Expr const & e)
+{
+    decltype(auto) expr = boost::yap::as_expr(e);
+    assert(equal_sizes(vec.size(), expr));
+    for (std::size_t i = 0, size = vec.size(); i < size; ++i) {
+        vec[i] = boost::yap::evaluate(
+            boost::yap::transform(boost::yap::as_expr(expr), take_nth{i}));
+    }
+    return vec;
+}
+
+// As assign() above, just using +=.
+template <typename T, typename Expr>
+std::vector<T> & operator+= (std::vector<T> & vec, Expr const & e)
+{
+    decltype(auto) expr = boost::yap::as_expr(e);
+    assert(equal_sizes(vec.size(), expr));
+    for (std::size_t i = 0, size = vec.size(); i < size; ++i) {
+        vec[i] += boost::yap::evaluate(
+            boost::yap::transform(boost::yap::as_expr(expr), take_nth{i}));
+    }
+    return vec;
+}
+
+// Define a type trait that identifies std::vectors.
+template <typename T>
+struct is_vector : std::false_type {};
+
+template <typename T, typename A>
+struct is_vector<std::vector<T, A>> : std::true_type {};
+
+// Define all the expression-returning numeric operators we need.  Each will
+// accept any std::vector<> as any of its arguments, and then any value in the
+// remaining argument, if any -- some of the operators below are unary.
+BOOST_YAP_USER_UDT_UNARY_OPERATOR(negate, boost::yap::expression, is_vector); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(multiplies, boost::yap::expression, is_vector); // *
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(divides, boost::yap::expression, is_vector); // /
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(modulus, boost::yap::expression, is_vector); // %
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(plus, boost::yap::expression, is_vector); // +
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(minus, boost::yap::expression, is_vector); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(less, boost::yap::expression, is_vector); // <
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(greater, boost::yap::expression, is_vector); // >
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(less_equal, boost::yap::expression, is_vector); // <=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(greater_equal, boost::yap::expression, is_vector); // >=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(equal_to, boost::yap::expression, is_vector); // ==
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(not_equal_to, boost::yap::expression, is_vector); // !=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(logical_or, boost::yap::expression, is_vector); // ||
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(logical_and, boost::yap::expression, is_vector); // &&
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_and, boost::yap::expression, is_vector); // &
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_or, boost::yap::expression, is_vector); // |
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(bitwise_xor, boost::yap::expression, is_vector); // ^
+
+int main()
+{
+    int i;
+    int const n = 10;
+    std::vector<int> a,b,c,d;
+    std::vector<double> e(n);
+
+    for (i = 0; i < n; ++i)
+    {
+        a.push_back(i);
+        b.push_back(2*i);
+        c.push_back(3*i);
+        d.push_back(i);
+    }
+
+    // After this point, no allocations occur.
+
+    assign(b, 2);
+    assign(d, a + b * c);
+
+    a += if_else(d < 30, b, c);
+
+    assign(e, c);
+    e += e - 4 / (c + 1);
+
+    for (i = 0; i < n; ++i)
+    {
+        std::cout
+            << " a(" << i << ") = " << a[i]
+            << " b(" << i << ") = " << b[i]
+            << " c(" << i << ") = " << c[i]
+            << " d(" << i << ") = " << d[i]
+            << " e(" << i << ") = " << e[i]
+            << std::endl;
+    }
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/index.html b/src/boost/libs/yap/index.html
new file mode 100644
index 00000000..ebb03015
--- /dev/null
+++ b/src/boost/libs/yap/index.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta http-equiv="refresh" content="0; URL=../../doc/html/yap.html">
+  </head>
+
+  <body>
+    Automatic redirection failed, click this <a href="../../doc/html/yap.html">link</a>
+    <hr>
+    <p>Copyright T. Zachary Laine 2016-2018</p>
+    <p>
+      Distributed under the Boost Software License, Version 1.0.
+      (See accompanying file <a href="LICENSE.md">LICENSE.md</a> or copy at
+      <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)
+    </p>
+  </body>
+</html>
diff --git a/src/boost/libs/yap/meta/libraries.json b/src/boost/libs/yap/meta/libraries.json
new file mode 100644
index 00000000..acd55688
--- /dev/null
+++ b/src/boost/libs/yap/meta/libraries.json
@@ -0,0 +1,8 @@
+{
+    "key": "yap",
+    "name": "YAP",
+    "authors": [ "T. Zachary Laine" ],
+    "maintainers": [ "Zach Laine <whatwasthataddress -at- gmail.com>" ],
+    "description": "An expression template library for C++14 and later.",
+    "category": [ "Generic", "Metaprogramming" ]
+}
diff --git a/src/boost/libs/yap/perf/CMakeLists.txt b/src/boost/libs/yap/perf/CMakeLists.txt
new file mode 100644
index 00000000..9c261491
--- /dev/null
+++ b/src/boost/libs/yap/perf/CMakeLists.txt
@@ -0,0 +1,55 @@
+include_directories(${CMAKE_HOME_DIRECTORY})
+
+
+macro(add_code_gen_executable name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name} yap)
+    if (clang_on_linux)
+        target_link_libraries(${name} c++)
+    endif ()
+endmacro()
+
+add_code_gen_executable(code_gen_samples)
+add_code_gen_executable(map_assign_code_gen)
+add_code_gen_executable(lazy_vector_perf)
+
+
+macro(add_perf_executable name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name} yap benchmark)
+    if (clang_on_linux)
+        target_link_libraries(${name} c++)
+    endif ()
+endmacro()
+
+add_perf_executable(map_assign_perf)
+add_perf_executable(arithmetic_perf)
+
+include(Disassemble)
+set(disassemble_dump_targets)
+foreach(fun eval_as_cpp_expr eval_as_yap_expr eval_as_cpp_expr_4x eval_as_yap_expr_4x)
+    disassemble(disassemble.arithmetic_perf.${fun} EXECUTABLE arithmetic_perf FUNCTION ${fun})
+    disassemble(disassemble.code_gen_samples.${fun} EXECUTABLE code_gen_samples FUNCTION ${fun})
+
+    add_custom_target(disass_dump.${fun}
+        COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} --target disassemble.arithmetic_perf.${fun}
+        COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} --target disassemble.code_gen_samples.${fun}
+    )
+    list(APPEND disassemble_dump_targets disass_dump.${fun})
+endforeach()
+
+foreach(fun get_d1_with_yap get_d1_by_hand update_v1_with_yap update_v1_by_hand)
+    disassemble(disassemble.lazy_vector_perf.${fun} EXECUTABLE lazy_vector_perf FUNCTION ${fun})
+
+    add_custom_target(disass_dump.${fun}
+        COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} --target disassemble.lazy_vector_perf.${fun}
+    )
+    list(APPEND disassemble_dump_targets disass_dump.${fun})
+endforeach()
+
+add_custom_target(perf
+    COMMAND map_assign_perf
+    COMMAND arithmetic_perf
+
+    DEPENDS ${disassemble_dump_targets}
+)
diff --git a/src/boost/libs/yap/perf/arithmetic_perf.cpp b/src/boost/libs/yap/perf/arithmetic_perf.cpp
new file mode 100644
index 00000000..bc3d4b49
--- /dev/null
+++ b/src/boost/libs/yap/perf/arithmetic_perf.cpp
@@ -0,0 +1,141 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <chrono>
+#include <iostream>
+
+#include <benchmark/benchmark.h>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+//[ arithmetic_perf_decls
+namespace user {
+
+    struct number
+    {
+        double value;
+
+        friend number operator+(number lhs, number rhs)
+        {
+            return number{lhs.value + rhs.value};
+        }
+
+        friend number operator*(number lhs, number rhs)
+        {
+            return number{lhs.value * rhs.value};
+        }
+    };
+}
+//]
+
+double get_noise()
+{
+    auto const start_time = std::chrono::high_resolution_clock::now();
+    auto const start_time_ns =
+        std::chrono::time_point_cast<std::chrono::nanoseconds>(start_time);
+    return 1.0 * start_time_ns.time_since_epoch().count();
+}
+
+
+user::number g_a{get_noise()};
+user::number g_x{get_noise()};
+user::number g_y{get_noise()};
+
+//[ arithmetic_perf_eval_as_yap_expr
+user::number eval_as_yap_expr(user::number a_, user::number x_, user::number y_)
+{
+    term<user::number> a{{a_}};
+    term<user::number> x{{x_}};
+    term<user::number> y{{y_}};
+    auto expr = (a * x + y) * (a * x + y) + (a * x + y);
+    return yap::evaluate(expr);
+}
+//]
+
+void BM_eval_as_yap_expr(benchmark::State & state)
+{
+    double d = 0;
+    while (state.KeepRunning()) {
+        user::number const n = eval_as_yap_expr(g_a, g_x, g_y);
+        d += n.value;
+    }
+    std::cout << "Sum of doubles=" << d << "\n";
+}
+
+//[ arithmetic_perf_eval_as_yap_expr_4x
+user::number
+eval_as_yap_expr_4x(user::number a_, user::number x_, user::number y_)
+{
+    term<user::number> a{{a_}};
+    term<user::number> x{{x_}};
+    term<user::number> y{{y_}};
+    auto expr = (a * x + y) * (a * x + y) + (a * x + y) +
+                (a * x + y) * (a * x + y) + (a * x + y) +
+                (a * x + y) * (a * x + y) + (a * x + y) +
+                (a * x + y) * (a * x + y) + (a * x + y);
+    return yap::evaluate(expr);
+}
+//]
+
+void BM_eval_as_yap_expr_4x(benchmark::State & state)
+{
+    double d = 0;
+    while (state.KeepRunning()) {
+        user::number const n = eval_as_yap_expr_4x(g_a, g_x, g_y);
+        d += n.value;
+    }
+    std::cout << "Sum of doubles=" << d << "\n";
+}
+
+//[ arithmetic_perf_eval_as_cpp_expr
+user::number eval_as_cpp_expr(user::number a, user::number x, user::number y)
+{
+    return (a * x + y) * (a * x + y) + (a * x + y);
+}
+//]
+
+void BM_eval_as_cpp_expr(benchmark::State & state)
+{
+    double d = 0;
+    while (state.KeepRunning()) {
+        user::number const n = eval_as_cpp_expr(g_a, g_x, g_y);
+        d += n.value;
+    }
+    std::cout << "Sum of doubles=" << d << "\n";
+}
+
+//[ arithmetic_perf_eval_as_cpp_expr_4x
+user::number eval_as_cpp_expr_4x(user::number a, user::number x, user::number y)
+{
+    return (a * x + y) * (a * x + y) + (a * x + y) + (a * x + y) * (a * x + y) +
+           (a * x + y) + (a * x + y) * (a * x + y) + (a * x + y) +
+           (a * x + y) * (a * x + y) + (a * x + y);
+}
+//]
+
+void BM_eval_as_cpp_expr_4x(benchmark::State & state)
+{
+    double d = 0;
+    while (state.KeepRunning()) {
+        user::number const n = eval_as_cpp_expr_4x(g_a, g_x, g_y);
+        d += n.value;
+    }
+    std::cout << "Sum of doubles=" << d << "\n";
+}
+
+BENCHMARK(BM_eval_as_yap_expr);
+BENCHMARK(BM_eval_as_yap_expr_4x);
+BENCHMARK(BM_eval_as_cpp_expr);
+BENCHMARK(BM_eval_as_cpp_expr_4x);
+
+BENCHMARK_MAIN()
diff --git a/src/boost/libs/yap/perf/code_gen_samples.cpp b/src/boost/libs/yap/perf/code_gen_samples.cpp
new file mode 100644
index 00000000..3df71b1c
--- /dev/null
+++ b/src/boost/libs/yap/perf/code_gen_samples.cpp
@@ -0,0 +1,99 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+namespace user {
+
+    struct number
+    {
+        double value;
+
+        friend number operator+(number lhs, number rhs)
+        {
+            return number{lhs.value + rhs.value};
+        }
+
+        friend number operator*(number lhs, number rhs)
+        {
+            return number{lhs.value * rhs.value};
+        }
+    };
+
+    // A more efficient fused multiply-add operation would normally go here.
+    number naxpy(number a, number x, number y)
+    {
+        return number{a.value * x.value + y.value};
+    }
+
+    // Transforms expressions of the form "a * x + y" to "naxpy(a, x, y)" via
+    // the implicit transform customiztion point.
+    template<typename Expr1, typename Expr2, typename Expr3>
+    decltype(auto) transform_expression(yap::expression<
+                                        yap::expr_kind::plus,
+                                        bh::tuple<
+                                            yap::expression<
+                                                yap::expr_kind::multiplies,
+                                                bh::tuple<Expr1, Expr2>>,
+                                            Expr3>> const & expr)
+    {
+        return naxpy(
+            evaluate(expr.left().left()),
+            evaluate(expr.left().right()),
+            evaluate(expr.right()));
+    }
+}
+
+term<user::number> a{{1.0}};
+term<user::number> x{{42.0}};
+term<user::number> y{{3.0}};
+
+user::number
+eval_as_yap_expr(decltype((a * x + y) * (a * x + y) + (a * x + y)) & expr)
+{
+    return yap::evaluate(expr);
+}
+
+user::number eval_as_yap_expr_4x(decltype(
+    (a * x + y) * (a * x + y) + (a * x + y) + (a * x + y) * (a * x + y) +
+    (a * x + y) + (a * x + y) * (a * x + y) + (a * x + y) +
+    (a * x + y) * (a * x + y) + (a * x + y)) & expr)
+{
+    return yap::evaluate(expr);
+}
+
+user::number eval_as_cpp_expr(user::number a, user::number x, user::number y)
+{
+    return (a * x + y) * (a * x + y) + (a * x + y);
+}
+
+user::number eval_as_cpp_expr_4x(user::number a, user::number x, user::number y)
+{
+    return (a * x + y) * (a * x + y) + (a * x + y) + (a * x + y) * (a * x + y) +
+           (a * x + y) + (a * x + y) * (a * x + y) + (a * x + y) +
+           (a * x + y) * (a * x + y) + (a * x + y);
+}
+
+
+int main()
+{
+    auto expr = (a * x + y) * (a * x + y) + (a * x + y);
+    user::number result_1 = eval_as_yap_expr(expr);
+    user::number result_2 =
+        eval_as_cpp_expr(yap::value(a), yap::value(x), yap::value(y));
+
+    (void)result_1;
+    (void)result_2;
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/perf/lazy_vector_perf.cpp b/src/boost/libs/yap/perf/lazy_vector_perf.cpp
new file mode 100644
index 00000000..e4099050
--- /dev/null
+++ b/src/boost/libs/yap/perf/lazy_vector_perf.cpp
@@ -0,0 +1,151 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ lazy_vector
+// Defining this allows the assignment below of an expression to a double
+// without writing any specific code to do so.
+#include <boost/yap/expression.hpp>
+
+#include <algorithm>
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr;
+
+
+// This transform turns a terminal of std::vector<double> into a terminal
+// containing the nth double in that vector.  Think of it as turning our
+// expression of vectors into an expression of scalars.
+struct take_nth
+{
+    boost::yap::terminal<lazy_vector_expr, double> operator()(
+        boost::yap::terminal<lazy_vector_expr, std::vector<double>> const &
+            expr);
+
+    std::size_t n;
+};
+
+// A custom expression template that defines lazy + and - operators that
+// produce expressions, and an eager [] operator that returns the nth element
+// of the expression.
+//[ lazy_vector_decl
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr
+{
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+
+    // Note that this does not return an expression; it is greedily evaluated.
+    auto operator[](std::size_t n) const;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, lazy_vector_expr, lazy_vector_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, lazy_vector_expr, lazy_vector_expr)
+//]
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+auto lazy_vector_expr<Kind, Tuple>::operator[](std::size_t n) const
+{
+    return boost::yap::evaluate(boost::yap::transform(*this, take_nth{n}));
+}
+
+boost::yap::terminal<lazy_vector_expr, double> take_nth::operator()(
+    boost::yap::terminal<lazy_vector_expr, std::vector<double>> const & expr)
+{
+    double x = boost::yap::value(expr)[n];
+    // This move is something of a hack.  The move indicates that the terminal
+    // should keep the value of x (since, being an rvalue, it may be a
+    // temporary), rather than a reference to x.  See the "How Expression
+    // Operands Are Treated" section of the tutorial for details.
+    return boost::yap::make_terminal<lazy_vector_expr, double>(std::move(x));
+}
+
+// In order to define the += operator with the semantics we want, it's
+// convenient to derive a terminal type from a terminal instantiation of
+// lazy_vector_expr.  note that we could have written a template
+// specialization here instead -- either one would work.  That would of course
+// have required more typing.
+struct lazy_vector : lazy_vector_expr<
+                         boost::yap::expr_kind::terminal,
+                         boost::hana::tuple<std::vector<double>>>
+{
+    lazy_vector() {}
+
+    explicit lazy_vector(std::vector<double> && vec)
+    {
+        elements = boost::hana::tuple<std::vector<double>>(std::move(vec));
+    }
+
+    template<boost::yap::expr_kind Kind, typename Tuple>
+    lazy_vector & operator+=(lazy_vector_expr<Kind, Tuple> const & rhs)
+    {
+        std::vector<double> & this_vec = boost::yap::value(*this);
+        for (int i = 0, size = (int)this_vec.size(); i < size; ++i) {
+            this_vec[i] += rhs[i];
+        }
+        return *this;
+    }
+};
+
+lazy_vector v1{std::vector<double>(4, 1.0)};
+lazy_vector v2{std::vector<double>(4, 2.0)};
+lazy_vector v3{std::vector<double>(4, 3.0)};
+
+double get_d1_with_yap()
+{
+    double retval = (v2 + v3)[2];
+    return retval;
+}
+
+double get_d1_by_hand()
+{
+    std::vector<double> & v2_ref = boost::yap::value(v2);
+    std::vector<double> & v3_ref = boost::yap::value(v3);
+    double retval = v2_ref[2] + v3_ref[2];
+    return retval;
+}
+
+void update_v1_with_yap() { v1 += v2 - v3; }
+
+void update_v1_by_hand()
+{
+    std::vector<double> & v1_ref = boost::yap::value(v1);
+    std::vector<double> & v2_ref = boost::yap::value(v2);
+    std::vector<double> & v3_ref = boost::yap::value(v3);
+    for (int i = 0, size = (int)v1_ref.size(); i < size; ++i) {
+        v1_ref[i] += v2_ref[i] - v3_ref[i];
+    }
+}
+
+int main()
+{
+    double d1_1 = get_d1_with_yap();
+    std::cout << d1_1 << "\n";
+
+    double d1_2 = get_d1_by_hand();
+    std::cout << d1_2 << "\n";
+
+    update_v1_with_yap();
+    std::cout << '{' << v1[0] << ',' << v1[1] << ',' << v1[2] << ',' << v1[3]
+              << '}' << "\n";
+
+    boost::yap::value(v1) = std::vector<double>(4, 1.0);
+
+    update_v1_by_hand();
+    std::cout << '{' << v1[0] << ',' << v1[1] << ',' << v1[2] << ',' << v1[3]
+              << '}' << "\n";
+
+    // This expression is disallowed because it does not conform to the
+    // implicit grammar.  operator+= is only defined on terminals, not
+    // arbitrary expressions.
+    // (v2 + v3) += v1;
+
+    return 0;
+}
+//]
diff --git a/src/boost/libs/yap/perf/map_assign_code_gen.cpp b/src/boost/libs/yap/perf/map_assign_code_gen.cpp
new file mode 100644
index 00000000..dc1fb777
--- /dev/null
+++ b/src/boost/libs/yap/perf/map_assign_code_gen.cpp
@@ -0,0 +1,149 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/assign/list_of.hpp>
+
+#include <map>
+#include <iostream>
+
+
+template<typename Key, typename Value, typename Allocator>
+struct map_list_of_transform
+{
+    template<typename Fn, typename Key2, typename Value2>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::call>,
+        Fn const & fn,
+        Key2 && key,
+        Value2 && value)
+    {
+        boost::yap::transform(
+            boost::yap::as_expr<boost::yap::minimal_expr>(fn), *this);
+        map.emplace(
+            Key{std::forward<Key2 &&>(key)},
+            Value{std::forward<Value2 &&>(value)});
+        return 0;
+    }
+
+    std::map<Key, Value, Allocator> map;
+};
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct map_list_of_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+
+    template<typename Key, typename Value, typename Allocator>
+    operator std::map<Key, Value, Allocator>() const
+    {
+        map_list_of_transform<Key, Value, Allocator> transform;
+        boost::yap::transform(*this, transform);
+        return transform.map;
+    }
+
+    BOOST_YAP_USER_CALL_OPERATOR(::map_list_of_expr)
+};
+
+struct map_list_of_tag
+{};
+
+auto map_list_of =
+    boost::yap::make_terminal<map_list_of_expr>(map_list_of_tag{});
+
+
+#if __GNUC__ || __clang__
+#define NOINLINE __attribute__((noinline))
+#else
+#define NOINLINE
+#endif
+
+
+NOINLINE std::map<std::string, int> make_map_with_boost_yap()
+{
+    return map_list_of("<", 1)("<=", 2)(">", 3)(">=", 4)("=", 5)("<>", 6);
+}
+
+
+NOINLINE std::map<std::string, int> make_map_with_boost_assign()
+{
+    return boost::assign::map_list_of("<", 1)("<=", 2)(">", 3)(">=", 4)("=", 5)(
+        "<>", 6);
+}
+
+
+NOINLINE std::map<std::string, int> make_map_manually()
+{
+    std::map<std::string, int> retval;
+    retval.emplace("<", 1);
+    retval.emplace("<=", 2);
+    retval.emplace(">", 3);
+    retval.emplace(">=", 4);
+    retval.emplace("=", 5);
+    retval.emplace("<>", 6);
+    return retval;
+}
+
+
+NOINLINE std::map<std::string, int> make_map_inializer_list()
+{
+    std::map<std::string, int> retval = {
+        {"<", 1}, {"<=", 2}, {">", 3}, {">=", 4}, {"=", 5}, {"<>", 6}};
+    return retval;
+}
+
+
+int main()
+{
+    {
+        std::map<std::string, int> op = make_map_with_boost_yap();
+
+        std::cout << "\"<\"  --> " << op["<"] << std::endl;
+        std::cout << "\"<=\" --> " << op["<="] << std::endl;
+        std::cout << "\">\"  --> " << op[">"] << std::endl;
+        std::cout << "\">=\" --> " << op[">="] << std::endl;
+        std::cout << "\"=\"  --> " << op["="] << std::endl;
+        std::cout << "\"<>\" --> " << op["<>"] << std::endl;
+    }
+
+    {
+        std::map<std::string, int> op = make_map_with_boost_assign();
+
+        std::cout << "\"<\"  --> " << op["<"] << std::endl;
+        std::cout << "\"<=\" --> " << op["<="] << std::endl;
+        std::cout << "\">\"  --> " << op[">"] << std::endl;
+        std::cout << "\">=\" --> " << op[">="] << std::endl;
+        std::cout << "\"=\"  --> " << op["="] << std::endl;
+        std::cout << "\"<>\" --> " << op["<>"] << std::endl;
+    }
+
+    {
+        std::map<std::string, int> op = make_map_manually();
+
+        std::cout << "\"<\"  --> " << op["<"] << std::endl;
+        std::cout << "\"<=\" --> " << op["<="] << std::endl;
+        std::cout << "\">\"  --> " << op[">"] << std::endl;
+        std::cout << "\">=\" --> " << op[">="] << std::endl;
+        std::cout << "\"=\"  --> " << op["="] << std::endl;
+        std::cout << "\"<>\" --> " << op["<>"] << std::endl;
+    }
+
+    {
+        std::map<std::string, int> op = make_map_inializer_list();
+
+        std::cout << "\"<\"  --> " << op["<"] << std::endl;
+        std::cout << "\"<=\" --> " << op["<="] << std::endl;
+        std::cout << "\">\"  --> " << op[">"] << std::endl;
+        std::cout << "\">=\" --> " << op[">="] << std::endl;
+        std::cout << "\"=\"  --> " << op["="] << std::endl;
+        std::cout << "\"<>\" --> " << op["<>"] << std::endl;
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/perf/map_assign_perf.cpp b/src/boost/libs/yap/perf/map_assign_perf.cpp
new file mode 100644
index 00000000..2253f3b6
--- /dev/null
+++ b/src/boost/libs/yap/perf/map_assign_perf.cpp
@@ -0,0 +1,162 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/assign/list_of.hpp>
+
+#include <map>
+#include <iostream>
+
+#include <benchmark/benchmark.h>
+
+
+template<typename Key, typename Value, typename Allocator>
+struct map_list_of_transform
+{
+    template<typename Fn, typename Key2, typename Value2>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::call>,
+        Fn const & fn,
+        Key2 && key,
+        Value2 && value)
+    {
+        boost::yap::transform(
+            boost::yap::as_expr<boost::yap::minimal_expr>(fn), *this);
+        map.emplace(
+            Key{std::forward<Key2 &&>(key)},
+            Value{std::forward<Value2 &&>(value)});
+        return 0;
+    }
+
+    std::map<Key, Value, Allocator> map;
+};
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct map_list_of_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+
+    template<typename Key, typename Value, typename Allocator>
+    operator std::map<Key, Value, Allocator>() const
+    {
+        map_list_of_transform<Key, Value, Allocator> transform;
+        boost::yap::transform(*this, transform);
+        return transform.map;
+    }
+
+    BOOST_YAP_USER_CALL_OPERATOR(::map_list_of_expr)
+};
+
+struct map_list_of_tag
+{};
+
+auto map_list_of =
+    boost::yap::make_terminal<map_list_of_expr>(map_list_of_tag{});
+
+
+std::map<std::string, int> make_map_with_boost_yap()
+{
+    return map_list_of("<", 1)("<=", 2)(">", 3)(">=", 4)("=", 5)("<>", 6);
+}
+
+void BM_make_map_with_boost_yap(benchmark::State & state)
+{
+    int i = 0;
+    while (state.KeepRunning()) {
+        {
+            std::map<std::string, int> map = make_map_with_boost_yap();
+            state.PauseTiming();
+            for (auto && x : map) {
+                i += x.second;
+            }
+        }
+        state.ResumeTiming();
+    }
+    std::cout << "Sum of ints in all maps made=" << i << "\n";
+}
+
+std::map<std::string, int> make_map_with_boost_assign()
+{
+    return boost::assign::map_list_of("<", 1)("<=", 2)(">", 3)(">=", 4)("=", 5)(
+        "<>", 6);
+}
+
+void BM_make_map_with_boost_assign(benchmark::State & state)
+{
+    int i = 0;
+    while (state.KeepRunning()) {
+        {
+            std::map<std::string, int> map = make_map_with_boost_assign();
+            state.PauseTiming();
+            for (auto && x : map) {
+                i += x.second;
+            }
+        }
+        state.ResumeTiming();
+    }
+    std::cout << "Sum of ints in all maps made=" << i << "\n";
+}
+
+std::map<std::string, int> make_map_manually()
+{
+    std::map<std::string, int> retval;
+    retval.emplace("<", 1);
+    retval.emplace("<=", 2);
+    retval.emplace(">", 3);
+    retval.emplace(">=", 4);
+    retval.emplace("=", 5);
+    retval.emplace("<>", 6);
+    return retval;
+}
+
+void BM_make_map_manually(benchmark::State & state)
+{
+    int i = 0;
+    while (state.KeepRunning()) {
+        {
+            std::map<std::string, int> map = make_map_manually();
+            state.PauseTiming();
+            for (auto && x : map) {
+                i += x.second;
+            }
+        }
+        state.ResumeTiming();
+    }
+    std::cout << "Sum of ints in all maps made=" << i << "\n";
+}
+
+std::map<std::string, int> make_map_inializer_list()
+{
+    std::map<std::string, int> retval = {
+        {"<", 1}, {"<=", 2}, {">", 3}, {">=", 4}, {"=", 5}, {"<>", 6}};
+    return retval;
+}
+
+void BM_make_map_inializer_list(benchmark::State & state)
+{
+    int i = 0;
+    while (state.KeepRunning()) {
+        {
+            std::map<std::string, int> map = make_map_inializer_list();
+            state.PauseTiming();
+            for (auto && x : map) {
+                i += x.second;
+            }
+        }
+        state.ResumeTiming();
+    }
+    std::cout << "Sum of ints in all maps made=" << i << "\n";
+}
+
+BENCHMARK(BM_make_map_with_boost_yap);
+BENCHMARK(BM_make_map_with_boost_assign);
+BENCHMARK(BM_make_map_manually);
+BENCHMARK(BM_make_map_inializer_list);
+
+BENCHMARK_MAIN()
diff --git a/src/boost/libs/yap/test/CMakeLists.txt b/src/boost/libs/yap/test/CMakeLists.txt
new file mode 100644
index 00000000..0188b806
--- /dev/null
+++ b/src/boost/libs/yap/test/CMakeLists.txt
@@ -0,0 +1,131 @@
+include_directories(${CMAKE_HOME_DIRECTORY})
+
+include(CTest)
+
+enable_testing()
+
+add_custom_target(yap_check COMMAND ${CMAKE_CTEST_COMMAND} -VV -C ${CMAKE_CFG_INTDIR})
+if (NOT TARGET check)
+    add_custom_target(check DEPENDS yap_check)
+else()
+    add_dependencies(check yap_check)
+endif()
+
+set(coverage_gcda_files)
+
+macro(add_test_executable name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name} yap)
+    target_compile_definitions(${name} PRIVATE BOOST_NO_AUTO_PTR)
+    add_test(${name} ${CMAKE_CURRENT_BINARY_DIR}/${name})
+    if (clang_on_linux)
+        target_link_libraries(${name} c++)
+    endif ()
+    list(APPEND coverage_gcda_files ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/${name}.dir/${name}.cpp.gcda)
+endmacro()
+
+add_test_executable(deref)
+add_test_executable(value)
+add_test_executable(left)
+add_test_executable(right)
+add_test_executable(print)
+add_test_executable(default_eval)
+add_test_executable(user_expression_transform_1)
+add_test_executable(user_expression_transform_2)
+add_test_executable(placeholder_eval)
+add_test_executable(call_expr)
+add_test_executable(reference_returns)
+add_test_executable(depth_stress_test_left)
+add_test_executable(depth_stress_test_right)
+add_test_executable(lazy_vector_alloc_test)
+add_test_executable(vector_alloc_test)
+add_test_executable(operators_unary)
+add_test_executable(comma)
+add_test_executable(if_else)
+add_test_executable(expression_function)
+add_test_executable(transform)
+
+add_executable(
+    compile_tests
+    compile_tests_main.cpp
+    compile_is_expr.cpp
+    compile_const_term.cpp
+    compile_placeholders.cpp
+    compile_term_plus_expr.cpp
+    compile_term_plus_term.cpp
+    compile_term_plus_x.cpp
+    compile_x_plus_term.cpp
+    compile_term_plus_x_this_ref_overloads.cpp
+    compile_const_term.cpp
+    compile_move_only_types.cpp
+    compile_user_macros.cpp
+)
+target_link_libraries(compile_tests yap)
+if (clang_on_linux)
+    target_link_libraries(compile_tests c++)
+endif ()
+
+function(add_compile_fail_test name)
+    try_compile(
+        compiles
+        ${CMAKE_BINARY_DIR}
+        ${CMAKE_CURRENT_SOURCE_DIR}/${name}.cpp
+        COMPILE_DEFINITIONS
+            ${std_flag} -I${Boost_INCLUDE_DIRS} -I${CMAKE_SOURCE_DIR}/include
+        OUTPUT_VARIABLE foo
+    )
+    #message("foo=${foo}")
+    if (compiles)
+        message(FATAL_ERROR "Compile-fail test ${name} does not fail to compile.")
+    endif ()
+endfunction()
+
+add_compile_fail_test(fail_transform)
+add_compile_fail_test(fail_get)
+add_compile_fail_test(fail_left)
+add_compile_fail_test(fail_right)
+add_compile_fail_test(fail_cond)
+add_compile_fail_test(fail_then)
+add_compile_fail_test(fail_else)
+add_compile_fail_test(fail_callable)
+add_compile_fail_test(fail_argument)
+add_compile_fail_test(fail_make_expression)
+add_compile_fail_test(fail_make_terminal)
+
+if (BUILD_COVERAGE AND UNIX)
+    if (APPLE)
+        add_custom_target(
+            coverage
+            rm -rf ${coverage_gcda_files} lcov-all.info lcov.info output
+            COMMAND
+                ${CMAKE_CTEST_COMMAND} -VV -C ${CMAKE_CFG_INTDIR}
+            COMMAND
+                cd ${CMAKE_BINARY_DIR}
+            COMMAND
+                llvm-cov gcov -f -b ${coverage_gcda_files}
+            COMMAND
+                lcov --directory . --base-directory . --gcov-tool ${CMAKE_SOURCE_DIR}/llvm-gcov.sh --capture -o lcov-all.info
+            COMMAND
+                lcov -e lcov-all.info ${CMAKE_SOURCE_DIR}/include/boost/yap/* ${CMAKE_SOURCE_DIR}/include/boost/yap/detail/* -o lcov.info
+            COMMAND
+                genhtml lcov.info -o output
+        )
+    else ()
+        add_custom_target(
+            coverage
+            rm -rf ${coverage_gcda_files} lcov-all.info lcov.info output
+            COMMAND
+                ${CMAKE_CTEST_COMMAND} -j4 -VV -C ${CMAKE_CFG_INTDIR}
+            COMMAND
+                cd ${CMAKE_BINARY_DIR}
+            COMMAND
+                gcov -f -b ${coverage_gcda_files}
+            COMMAND
+                lcov --directory . --base-directory . --capture -o lcov-all.info
+            COMMAND
+                lcov -e lcov-all.info ${CMAKE_SOURCE_DIR}/include/boost/yap/* ${CMAKE_SOURCE_DIR}/include/boost/yap/detail/* -o lcov.info
+            COMMAND
+                genhtml lcov.info -o output
+        )
+    endif ()
+endif ()
diff --git a/src/boost/libs/yap/test/Jamfile.v2 b/src/boost/libs/yap/test/Jamfile.v2
new file mode 100644
index 00000000..17bfd90c
--- /dev/null
+++ b/src/boost/libs/yap/test/Jamfile.v2
@@ -0,0 +1,63 @@
+# Copyright (c) 2018
+# T. Zachary Laine
+#
+# Distributed under the Boost Software License, Version 1.0. (See
+# accompanying file LICENSE_1_0.txt or copy at
+# http://www.boost.org/LICENSE_1_0.txt
+
+import config : requires ;
+import testing ;
+
+project
+    : requirements
+        [ requires
+            cxx14_constexpr
+            cxx14_decltype_auto
+            cxx14_generic_lambdas
+            cxx14_return_type_deduction
+        ]
+    ;
+
+run deref.cpp ;
+run value.cpp ;
+run left.cpp ;
+run right.cpp ;
+run print.cpp ;
+run default_eval.cpp ;
+run user_expression_transform_1.cpp ;
+run user_expression_transform_2.cpp ;
+run placeholder_eval.cpp ;
+run call_expr.cpp ;
+run reference_returns.cpp ;
+run depth_stress_test_left.cpp ;
+run depth_stress_test_right.cpp ;
+run lazy_vector_alloc_test.cpp ;
+run vector_alloc_test.cpp ;
+run operators_unary.cpp ;
+run comma.cpp ;
+run if_else.cpp ;
+run expression_function.cpp ;
+run transform.cpp ;
+
+compile compile_is_expr.cpp ;
+compile compile_const_term.cpp ;
+compile compile_placeholders.cpp ;
+compile compile_term_plus_expr.cpp ;
+compile compile_term_plus_term.cpp ;
+compile compile_term_plus_x.cpp ;
+compile compile_x_plus_term.cpp ;
+compile compile_term_plus_x_this_ref_overloads.cpp ;
+compile compile_move_only_types.cpp ;
+compile compile_user_macros.cpp ;
+
+compile-fail fail_transform.cpp ;
+compile-fail fail_get.cpp ;
+compile-fail fail_left.cpp ;
+compile-fail fail_right.cpp ;
+compile-fail fail_cond.cpp ;
+compile-fail fail_then.cpp ;
+compile-fail fail_else.cpp ;
+compile-fail fail_callable.cpp ;
+compile-fail fail_argument.cpp ;
+compile-fail fail_make_expression.cpp ;
+compile-fail fail_make_terminal.cpp ;
diff --git a/src/boost/libs/yap/test/call_expr.cpp b/src/boost/libs/yap/test/call_expr.cpp
new file mode 100644
index 00000000..2e5c343f
--- /dev/null
+++ b/src/boost/libs/yap/test/call_expr.cpp
@@ -0,0 +1,198 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+namespace user {
+
+    struct number
+    {
+        explicit operator double() const { return value; }
+
+        double value;
+    };
+
+    number naxpy(number a, number x, number y)
+    {
+        return number{a.value * x.value + y.value + 10.0};
+    }
+
+    struct tag_type
+    {};
+
+    inline number tag_function(double a, double b) { return number{a + b}; }
+
+    struct eval_xform_tag
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::call>, tag_type, number a, double b)
+        {
+            return tag_function(a.value, b);
+        }
+
+        int operator()(
+            yap::expr_tag<yap::expr_kind::call>, tag_type, double a, double b)
+        {
+            return 42;
+        }
+
+        char const * operator()() { return "42"; }
+    };
+
+    struct empty_xform
+    {};
+
+    struct eval_xform_expr
+    {
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::call,
+                                  bh::tuple<
+                                      ref<term<user::tag_type>>,
+                                      term<user::number>,
+                                      term<int>>> const & expr)
+        {
+            using namespace boost::hana::literals;
+            return tag_function(
+                (double)yap::value(expr.elements[1_c]).value,
+                (double)yap::value(expr.elements[2_c]));
+        }
+
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::call,
+                                  bh::tuple<
+                                      ref<term<user::tag_type>>,
+                                      ref<term<user::number>>,
+                                      term<int>>> const & expr)
+        {
+            using namespace boost::hana::literals;
+            return tag_function(
+                (double)yap::value(expr.elements[1_c]).value,
+                (double)yap::value(expr.elements[2_c]));
+        }
+    };
+
+    struct eval_xform_both
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::call>,
+            tag_type,
+            user::number a,
+            double b)
+        {
+            return tag_function(a.value, b);
+        }
+
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::call,
+                                  bh::tuple<
+                                      ref<term<user::tag_type>>,
+                                      term<user::number>,
+                                      term<int>>> const & expr)
+        {
+            using namespace boost::hana::literals;
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return tag_function(
+                (double)yap::value(expr.elements[1_c]).value,
+                (double)yap::value(expr.elements[2_c]));
+        }
+
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::call,
+                                  bh::tuple<
+                                      ref<term<user::tag_type>>,
+                                      ref<term<user::number>>,
+                                      term<int>>> const & expr)
+        {
+            using namespace boost::hana::literals;
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return tag_function(
+                (double)yap::value(expr.elements[1_c]).value,
+                (double)yap::value(expr.elements[2_c]));
+        }
+    };
+}
+
+
+int test_main(int, char * [])
+{
+    {
+        using namespace boost::yap::literals;
+
+        {
+            auto plus = yap::make_terminal(user::tag_type{});
+            auto expr = plus(user::number{13}, 1);
+
+            {
+                transform(expr, user::empty_xform{});
+            }
+
+            {
+                user::number result = transform(expr, user::eval_xform_tag{});
+                BOOST_CHECK(result.value == 14);
+            }
+
+            {
+                user::number result = transform(expr, user::eval_xform_expr{});
+                BOOST_CHECK(result.value == 14);
+            }
+
+            {
+                user::number result = transform(expr, user::eval_xform_both{});
+                BOOST_CHECK(result.value == 14);
+            }
+        }
+
+        {
+            auto plus = yap::make_terminal(user::tag_type{});
+            auto thirteen = yap::make_terminal(user::number{13});
+            auto expr = plus(thirteen, 1);
+
+            {
+                user::number result = transform(expr, user::eval_xform_tag{});
+                BOOST_CHECK(result.value == 14);
+            }
+
+            {
+                user::number result = transform(expr, user::eval_xform_expr{});
+                BOOST_CHECK(result.value == 14);
+            }
+
+            {
+                user::number result = transform(expr, user::eval_xform_both{});
+                BOOST_CHECK(result.value == 14);
+            }
+        }
+
+        {
+            term<user::number> a{{1.0}};
+            term<user::number> x{{42.0}};
+            term<user::number> y{{3.0}};
+            auto n = yap::make_terminal(user::naxpy);
+
+            auto expr = n(a, x, y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 55);
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/comma.cpp b/src/boost/libs/yap/test/comma.cpp
new file mode 100644
index 00000000..af3814cf
--- /dev/null
+++ b/src/boost/libs/yap/test/comma.cpp
@@ -0,0 +1,126 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using term_ref = boost::yap::expression_ref<boost::yap::expression, term<T> &>;
+
+template<typename T>
+using term_cref =
+    boost::yap::expression_ref<boost::yap::expression, term<T> const &>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+struct void_callable
+{
+    void operator()() { *called_ = (*call_count_)++; }
+    int * call_count_;
+    int * called_;
+};
+
+struct int_callable
+{
+    int operator()()
+    {
+        *called_ = (*call_count_)++;
+        return 42;
+    }
+    int * call_count_;
+    int * called_;
+};
+
+struct double_callable
+{
+    double operator()()
+    {
+        *called_ = (*call_count_)++;
+        return 13.0;
+    }
+    int * call_count_;
+    int * called_;
+};
+
+
+int test_main(int, char * [])
+{
+{
+    {
+        int call_count = 0;
+        int int_called = -1;
+        int double_called = -1;
+
+        auto int_double_expr =
+            (term<int_callable>{{&call_count, &int_called}}(),
+             term<double_callable>{{&call_count, &double_called}}());
+
+        BOOST_CHECK(evaluate(int_double_expr) == 13.0);
+        BOOST_CHECK(int_called == 0);
+        BOOST_CHECK(double_called == 1);
+    }
+
+    {
+        int call_count = 0;
+        int int_called = -1;
+        int double_called = -1;
+
+        auto double_int_expr =
+            (term<double_callable>{{&call_count, &double_called}}(),
+             term<int_callable>{{&call_count, &int_called}}());
+
+        BOOST_CHECK(evaluate(double_int_expr) == 42);
+        BOOST_CHECK(int_called == 1);
+        BOOST_CHECK(double_called == 0);
+    }
+}
+
+{
+    {
+        int call_count = 0;
+        int void_called = -1;
+        int int_called = -1;
+
+        auto void_int_expr =
+            (term<void_callable>{{&call_count, &void_called}}(),
+             term<int_callable>{{&call_count, &int_called}}());
+
+        BOOST_CHECK(evaluate(void_int_expr) == 42);
+        BOOST_CHECK(void_called == 0);
+        BOOST_CHECK(int_called == 1);
+    }
+
+    {
+        int call_count = 0;
+        int void_called = -1;
+        int int_called = -1;
+
+        auto int_void_expr =
+            (term<int_callable>{{&call_count, &int_called}}(),
+             term<void_callable>{{&call_count, &void_called}}());
+
+        using eval_type = decltype(evaluate(int_void_expr));
+        BOOST_MPL_ASSERT(
+            (std::is_same<void, eval_type>));
+
+        evaluate(int_void_expr);
+        BOOST_CHECK(void_called == 1);
+        BOOST_CHECK(int_called == 0);
+    }
+}
+
+return 0;
+}
diff --git a/src/boost/libs/yap/test/compile_const_term.cpp b/src/boost/libs/yap/test/compile_const_term.cpp
new file mode 100644
index 00000000..11ff761d
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_const_term.cpp
@@ -0,0 +1,77 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_const_term()
+{
+    {
+        term<double const> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double const> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double const> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double const> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> const unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> const &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> const &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> const &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int const &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const &>>> const expr =
+            unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int const &>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_is_expr.cpp b/src/boost/libs/yap/test/compile_is_expr.cpp
new file mode 100644
index 00000000..3bf030d4
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_is_expr.cpp
@@ -0,0 +1,99 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+namespace yap = boost::yap;
+
+struct alternate_expr_1
+{
+    static const yap::expr_kind kind = yap::expr_kind::plus;
+    boost::hana::tuple<> elements;
+};
+
+struct alternate_expr_2
+{
+    static const yap::expr_kind kind = yap::expr_kind::plus;
+    boost::hana::tuple<int, double> elements;
+};
+
+
+struct non_expr_1
+{};
+
+struct non_expr_2
+{
+    boost::hana::tuple<int, double> elements;
+};
+
+struct non_expr_3
+{
+    static const int kind = 0;
+    boost::hana::tuple<int, double> elements;
+};
+
+struct non_expr_4
+{
+    int kind;
+    boost::hana::tuple<int, double> elements;
+};
+
+struct non_expr_5
+{
+    static const yap::expr_kind kind = yap::expr_kind::plus;
+};
+
+struct non_expr_6
+{
+    static const yap::expr_kind kind = yap::expr_kind::plus;
+    int elements;
+};
+
+
+void compile_is_expr()
+{
+    static_assert(
+        yap::is_expr<yap::terminal<yap::expression, double>>::value, "");
+
+    static_assert(
+        yap::is_expr<yap::terminal<yap::expression, double> const>::value, "");
+    static_assert(
+        yap::is_expr<yap::terminal<yap::expression, double> const &>::value,
+        "");
+    static_assert(
+        yap::is_expr<yap::terminal<yap::expression, double> &>::value, "");
+    static_assert(
+        yap::is_expr<yap::terminal<yap::expression, double> &&>::value, "");
+
+    {
+        using namespace yap::literals;
+        static_assert(yap::is_expr<decltype(1_p)>::value, "");
+    }
+
+    static_assert(
+        yap::is_expr<yap::expression<
+            yap::expr_kind::unary_plus,
+            boost::hana::tuple<yap::terminal<yap::expression, double>>>>::value,
+        "");
+    static_assert(
+        yap::is_expr<yap::expression<
+            yap::expr_kind::plus,
+            boost::hana::tuple<
+                yap::terminal<yap::expression, double>,
+                yap::terminal<yap::expression, double>>>>::value,
+        "");
+
+    static_assert(yap::is_expr<alternate_expr_1>::value, "");
+    static_assert(yap::is_expr<alternate_expr_2>::value, "");
+
+    static_assert(!yap::is_expr<int>::value, "");
+    static_assert(!yap::is_expr<non_expr_1>::value, "");
+    static_assert(!yap::is_expr<non_expr_2>::value, "");
+    static_assert(!yap::is_expr<non_expr_3>::value, "");
+    static_assert(!yap::is_expr<non_expr_4>::value, "");
+    static_assert(!yap::is_expr<non_expr_5>::value, "");
+    static_assert(!yap::is_expr<non_expr_6>::value, "");
+}
diff --git a/src/boost/libs/yap/test/compile_move_only_types.cpp b/src/boost/libs/yap/test/compile_move_only_types.cpp
new file mode 100644
index 00000000..2649ff00
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_move_only_types.cpp
@@ -0,0 +1,46 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <memory>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+inline auto double_to_float(term<double> expr)
+{
+    return term<float>{(float)expr.value()};
+}
+
+void compile_move_only_types()
+{
+    term<double> unity{1.0};
+    term<std::unique_ptr<int>> i{new int{7}};
+    yap::expression<
+        yap::expr_kind::plus,
+        bh::tuple<ref<term<double> &>, term<std::unique_ptr<int>>>>
+        expr_1 = unity + std::move(i);
+
+    yap::expression<
+        yap::expr_kind::plus,
+        bh::tuple<
+            ref<term<double> &>,
+            yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> &>, term<std::unique_ptr<int>>>>>>
+        expr_2 = unity + std::move(expr_1);
+
+    auto transformed_expr = transform(std::move(expr_2), double_to_float);
+    (void)transformed_expr;
+}
diff --git a/src/boost/libs/yap/test/compile_placeholders.cpp b/src/boost/libs/yap/test/compile_placeholders.cpp
new file mode 100644
index 00000000..8a4e50aa
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_placeholders.cpp
@@ -0,0 +1,50 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<long long I>
+using place_term =
+    boost::yap::terminal<boost::yap::expression, boost::yap::placeholder<I>>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_placeholders()
+{
+    using namespace boost::yap::literals;
+
+    {
+        place_term<1> p1 = 1_p;
+        (void)p1;
+    }
+
+    {
+        place_term<1> p1 = 1_p;
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<place_term<1> &>, ref<term<double> &>>>
+            expr = p1 + unity;
+        (void)expr;
+    }
+
+    {
+        place_term<1> p1 = 1_p;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<place_term<1> &>, place_term<2>>>
+            expr = p1 + 2_p;
+        (void)expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_term_plus_expr.cpp b/src/boost/libs/yap/test/compile_term_plus_expr.cpp
new file mode 100644
index 00000000..9a90f9ac
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_term_plus_expr.cpp
@@ -0,0 +1,308 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_term_plus_expr()
+{
+    // values
+    {
+        term<double> unity{1.0};
+        term<int> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int> &>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int const> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int const> &>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    // const value terminals/expressions
+    {
+        term<double> unity{1.0};
+        term<int> const i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int> const &>>> const expr =
+            unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<
+                        ref<term<double> &>,
+                        ref<term<int> const &>>> const &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int> &>>> const expr =
+            unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int> &>>> const &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    // lvalue refs
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int &> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int &> &>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int const &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const &> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<
+                        ref<term<double> &>,
+                        ref<term<int const &> &>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                ref<yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &>>> &>>>
+            unevaluated_expr = unity + expr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int &> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int &> &>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int const &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const &> &>>>
+            expr = unity + i;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, ref<term<int const &> &>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    // rvalue refs
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_term_plus_term.cpp b/src/boost/libs/yap/test/compile_term_plus_term.cpp
new file mode 100644
index 00000000..d1037ce6
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_term_plus_term.cpp
@@ -0,0 +1,221 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <string>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_term_plus_term()
+{
+    using namespace std::literals;
+
+    // char const * string
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<char const *>>>
+            unevaluated_expr = unity + term<char const *>{"3"};
+        (void)unevaluated_expr;
+    }
+
+    // std::string temporary
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<std::string>>>
+            unevaluated_expr = unity + term<std::string>{"3"s};
+        (void)unevaluated_expr;
+    }
+
+    // pointers
+    {
+        term<double> unity{1.0};
+        int ints_[] = {1, 2};
+        term<int *> ints = {ints_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int *> &>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints_[] = {1, 2};
+        term<int const *> ints = {ints_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const *> &>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints_[] = {1, 2};
+        term<int *> ints = {ints_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + std::move(ints);
+        (void)unevaluated_expr;
+    }
+
+    // const pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        term<int * const> int_ptr = {ints};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int * const> &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        term<int const * const> int_ptr = {ints};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const * const> &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        term<int * const> int_ptr = {ints};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int * const>>>
+            unevaluated_expr = unity + std::move(int_ptr);
+        (void)unevaluated_expr;
+    }
+
+    // values
+    {
+        term<double> unity{1.0};
+        term<int> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int> &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int const> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const> &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int> i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+
+    // const value terminals
+    {
+        term<double> unity{1.0};
+        term<int> const i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int> const &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        term<int const> const i = {1};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const> const &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    // lvalue refs
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int &> &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int const &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<int const &> &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &> i{i_};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+
+    // rvalue refs
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 1;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_term_plus_x.cpp b/src/boost/libs/yap/test/compile_term_plus_x.cpp
new file mode 100644
index 00000000..1382abf9
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_term_plus_x.cpp
@@ -0,0 +1,174 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <string>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_term_plus_x()
+{
+    using namespace std::literals;
+
+    // char const * string
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<char const *>>>
+            unevaluated_expr = unity + "3";
+        (void)unevaluated_expr;
+    }
+
+    // std::string temporary
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<std::string>>>
+            unevaluated_expr = unity + "3"s;
+        (void)unevaluated_expr;
+    }
+
+    // arrays
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const *>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + std::move(ints);
+        (void)unevaluated_expr;
+    }
+
+    // pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *&>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const *&>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + std::move(int_ptr);
+        (void)unevaluated_expr;
+    }
+
+    // const pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int * const &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const * const &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int * const>>>
+            unevaluated_expr = unity + std::move(int_ptr);
+        (void)unevaluated_expr;
+    }
+
+    // values
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_term_plus_x_this_ref_overloads.cpp b/src/boost/libs/yap/test/compile_term_plus_x_this_ref_overloads.cpp
new file mode 100644
index 00000000..58541609
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_term_plus_x_this_ref_overloads.cpp
@@ -0,0 +1,174 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <string>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_term_plus_x_this_ref_overloads()
+{
+    using namespace std::literals;
+
+    // char const * string
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<char const *>>>
+            unevaluated_expr = unity + "3";
+        (void)unevaluated_expr;
+    }
+
+    // std::string temporary
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<std::string>>>
+            unevaluated_expr = unity + "3"s;
+        (void)unevaluated_expr;
+    }
+
+    // arrays
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const *>>>
+            unevaluated_expr = unity + ints;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + std::move(ints);
+        (void)unevaluated_expr;
+    }
+
+    // pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *&>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const *&>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int *>>>
+            unevaluated_expr = unity + std::move(int_ptr);
+        (void)unevaluated_expr;
+    }
+
+    // const pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int * const &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const * const &>>>
+            unevaluated_expr = unity + int_ptr;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int * const>>>
+            unevaluated_expr = unity + std::move(int_ptr);
+        (void)unevaluated_expr;
+    }
+
+    // values
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int const &>>>
+            unevaluated_expr = unity + i;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>
+            unevaluated_expr = unity + std::move(i);
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/compile_tests_main.cpp b/src/boost/libs/yap/test/compile_tests_main.cpp
new file mode 100644
index 00000000..7c77fc4e
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_tests_main.cpp
@@ -0,0 +1,29 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+void compile_is_expr();
+void compile_const_term();
+void compile_move_only_types();
+void compile_placeholders();
+void compile_term_plus_expr();
+void compile_term_plus_term();
+void compile_term_plus_x();
+void compile_term_plus_x_this_ref_overloads();
+void compile_x_plus_term();
+void compile_user_macros();
+
+int main()
+{
+    compile_is_expr();
+    compile_const_term();
+    compile_move_only_types();
+    compile_placeholders();
+    compile_term_plus_expr();
+    compile_term_plus_term();
+    compile_term_plus_x();
+    compile_term_plus_x_this_ref_overloads();
+    compile_x_plus_term();
+    compile_user_macros();
+}
diff --git a/src/boost/libs/yap/test/compile_user_macros.cpp b/src/boost/libs/yap/test/compile_user_macros.cpp
new file mode 100644
index 00000000..f9fd01f4
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_user_macros.cpp
@@ -0,0 +1,58 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<yap::expr_kind Kind, typename Tuple>
+struct expr
+{
+    static yap::expr_kind const kind = Kind;
+    Tuple elements;
+
+    BOOST_YAP_USER_ASSIGN_OPERATOR(expr, ::expr);
+};
+
+
+static_assert(yap::detail::copy_or_move<int, int const &>::value, "");
+static_assert(yap::detail::copy_or_move<int, int &>::value, "");
+static_assert(yap::detail::copy_or_move<int, int &&>::value, "");
+static_assert(!yap::detail::copy_or_move<int, int const &&>::value, "");
+static_assert(!yap::detail::copy_or_move<int, int>::value, "");
+
+
+void compile_user_macros()
+{
+    using namespace boost::hana::literals;
+
+    expr<yap::expr_kind::negate, bh::tuple<int>> negation1;
+    negation1.elements[0_c] = 1;
+    expr<yap::expr_kind::negate, bh::tuple<int>> negation2;
+    negation2.elements[0_c] = 2;
+
+    // Normal-rules assignment.
+    negation2 = negation1;
+    assert(negation2.elements[0_c] == 1);
+
+    negation2.elements[0_c] = 2;
+
+    // Normal-rules move assignment.
+    negation2 = std::move(negation1);
+    assert(negation2.elements[0_c] == 1);
+
+    // Produce a new expression via BOOST_YAP_USER_ASSIGN_OPERATOR.
+    auto expr = negation1 = 2;
+    (void)expr;
+}
diff --git a/src/boost/libs/yap/test/compile_x_plus_term.cpp b/src/boost/libs/yap/test/compile_x_plus_term.cpp
new file mode 100644
index 00000000..2eef6eba
--- /dev/null
+++ b/src/boost/libs/yap/test/compile_x_plus_term.cpp
@@ -0,0 +1,174 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <string>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+void compile_x_plus_term()
+{
+    using namespace std::literals;
+
+    // char const * string
+    {
+        term<double> unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<char const *>, ref<term<double> &>>>
+            unevaluated_expr = "3" + unity;
+        (void)unevaluated_expr;
+    }
+
+    // std::string temporary
+    {
+        term<double> const unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<std::string>, ref<term<double> const &>>>
+            unevaluated_expr = "3"s + unity;
+        (void)unevaluated_expr;
+    }
+
+    // arrays
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int *>, ref<term<double> &>>>
+            unevaluated_expr = ints + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int const *>, ref<term<double> &>>>
+            unevaluated_expr = ints + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int *>, ref<term<double> &>>>
+            unevaluated_expr = std::move(ints) + unity;
+        (void)unevaluated_expr;
+    }
+
+    // pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int *&>, ref<term<double> &>>>
+            unevaluated_expr = int_ptr + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int const *&>, ref<term<double> &>>>
+            unevaluated_expr = int_ptr + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int *>, ref<term<double> &>>>
+            unevaluated_expr = std::move(int_ptr) + unity;
+        (void)unevaluated_expr;
+    }
+
+    // const pointers
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int * const &>, ref<term<double> &>>>
+            unevaluated_expr = int_ptr + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const ints[] = {1, 2};
+        int const * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int const * const &>, ref<term<double> &>>>
+            unevaluated_expr = int_ptr + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int ints[] = {1, 2};
+        int * const int_ptr = ints;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int * const>, ref<term<double> &>>>
+            unevaluated_expr = std::move(int_ptr) + unity;
+        (void)unevaluated_expr;
+    }
+
+    // values
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int &>, ref<term<double> &>>>
+            unevaluated_expr = i + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int const i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int const &>, ref<term<double> &>>>
+            unevaluated_expr = i + unity;
+        (void)unevaluated_expr;
+    }
+
+    {
+        term<double> unity{1.0};
+        int i = 1;
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<term<int>, ref<term<double> &>>>
+            unevaluated_expr = std::move(i) + unity;
+        (void)unevaluated_expr;
+    }
+}
diff --git a/src/boost/libs/yap/test/default_eval.cpp b/src/boost/libs/yap/test/default_eval.cpp
new file mode 100644
index 00000000..27087f95
--- /dev/null
+++ b/src/boost/libs/yap/test/default_eval.cpp
@@ -0,0 +1,103 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::minus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity - std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::minus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr_1 = unity + std::move(expr);
+
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<double> &>>>
+            unevaluated_expr_2 = unity + unity;
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            unevaluated_expr_3 = unity + const_unity;
+
+        {
+            double result = evaluate(unity);
+            BOOST_CHECK(result == 1);
+        }
+
+        {
+            double result = evaluate(expr);
+            BOOST_CHECK(result == -41);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_1);
+            BOOST_CHECK(result == -40);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_2);
+            BOOST_CHECK(result == 2);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_3);
+            BOOST_CHECK(result == 2);
+        }
+
+        {
+            double result = evaluate(unity, 5, 6, 7);
+            BOOST_CHECK(result == 1);
+        }
+
+        {
+            double result = evaluate(expr);
+            BOOST_CHECK(result == -41);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_1, std::string("15"));
+            BOOST_CHECK(result == -40);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_2, std::string("15"));
+            BOOST_CHECK(result == 2);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr_3, std::string("15"));
+            BOOST_CHECK(result == 2);
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/depth_stress_test_left.cpp b/src/boost/libs/yap/test/depth_stress_test_left.cpp
new file mode 100644
index 00000000..ec2724e1
--- /dev/null
+++ b/src/boost/libs/yap/test/depth_stress_test_left.cpp
@@ -0,0 +1,69 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template <typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+
+
+int test_main(int, char * [])
+{
+{
+    term<double> unity{1.0};
+
+    {
+        auto expr = (unity + (unity + (unity + (unity +    (unity + (unity + (unity + unity)))))));
+        double result = boost::yap::evaluate(expr);
+        BOOST_CHECK(result == 8.0);
+    }
+
+    {
+        auto expr =
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))));
+        double result = boost::yap::evaluate(expr);
+        BOOST_CHECK(result == 64.0);
+    }
+
+#if 0 // This makes the Travis VMs barf.
+    {
+        auto expr =
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity +
+            (unity + (unity + (unity + (unity +    (unity + (unity + (unity + (unity))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))));
+        double result = boost::yap::evaluate(
+            (expr + (expr + (expr + (expr +    (expr + (expr + (expr + (expr +
+            (expr + (expr + (expr + (expr +    (expr + (expr + (expr + (expr +
+            (expr + (expr + (expr + (expr +    (expr + (expr + (expr + (expr +
+            (expr + (expr + (expr + (expr +    (expr + (expr + (expr + (expr))))))))))))))))))))))))))))))))
+        );
+        BOOST_CHECK(result == 64.0 * 32.0);
+    }
+#endif
+}
+
+return 0;
+}
diff --git a/src/boost/libs/yap/test/depth_stress_test_right.cpp b/src/boost/libs/yap/test/depth_stress_test_right.cpp
new file mode 100644
index 00000000..33c5be1b
--- /dev/null
+++ b/src/boost/libs/yap/test/depth_stress_test_right.cpp
@@ -0,0 +1,70 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<double> unity{1.0};
+
+        {
+            auto expr =
+                unity + unity + unity + unity + unity + unity + unity + unity;
+            double result = boost::yap::evaluate(expr);
+            BOOST_CHECK(result == 8.0);
+        }
+
+        {
+            auto expr =
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity +
+
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity +
+                unity + unity + unity + unity + unity + unity + unity + unity;
+            double result = boost::yap::evaluate(expr);
+            BOOST_CHECK(result == 64.0);
+        }
+
+#if 0 // This makes the Travis VMs barf.
+    {
+        auto expr =
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity +
+            unity + unity + unity + unity +    unity + unity + unity + unity;
+        double result = boost::yap::evaluate(
+            expr + expr + expr + expr +    expr + expr + expr + expr +
+            expr + expr + expr + expr +    expr + expr + expr + expr +
+            expr + expr + expr + expr +    expr + expr + expr + expr +
+            expr + expr + expr + expr +    expr + expr + expr + expr
+        );
+        BOOST_CHECK(result == 64.0 * 32.0);
+    }
+#endif
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/deref.cpp b/src/boost/libs/yap/test/deref.cpp
new file mode 100644
index 00000000..137b51e8
--- /dev/null
+++ b/src/boost/libs/yap/test/deref.cpp
@@ -0,0 +1,174 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct user_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, user_expr, user_expr)
+
+template<typename T>
+using user_term = boost::yap::terminal<user_expr, T>;
+
+template<typename T>
+using user_ref = boost::yap::expression_ref<user_expr, T>;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<double> unity = {{1.0}};
+        using plus_expr_type = yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>;
+
+        plus_expr_type plus_expr = unity + term<int>{{1}};
+
+        {
+            ref<term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::deref(std::move(ref))),
+                              term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            ref<term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::deref(ref)), term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            ref<term<double> &> const ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::deref(ref)), term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            term<double> const unity = {{1.0}};
+            yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> const &>, term<int>>>
+                plus_expr = unity + term<int>{{1}};
+
+            {
+                ref<term<double> const &> ref = bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(std::move(ref))),
+                                  term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+
+            {
+                ref<term<double> const &> ref = bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(ref)),
+                                  term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+
+            {
+                ref<term<double> const &> const ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(ref)),
+                                  term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+        }
+    }
+
+    {
+        user_term<double> unity = {{1.0}};
+        using plus_expr_type = user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+
+        plus_expr_type plus_expr = unity + user_term<int>{{1}};
+
+        {
+            user_ref<user_term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::deref(std::move(ref))),
+                              user_term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            user_ref<user_term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::deref(ref)), user_term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            user_ref<user_term<double> &> const ref =
+                bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::deref(ref)), user_term<double> &>));
+            BOOST_CHECK(yap::value(ref) == 1.0);
+        }
+
+        {
+            user_term<double> const unity = {{1.0}};
+            user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> const &>, user_term<int>>>
+                plus_expr = unity + user_term<int>{{1}};
+
+            {
+                user_ref<user_term<double> const &> ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(std::move(ref))),
+                                  user_term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+
+            {
+                user_ref<user_term<double> const &> ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(ref)),
+                                  user_term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+
+            {
+                user_ref<user_term<double> const &> const ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::deref(ref)),
+                                  user_term<double> const &>));
+                BOOST_CHECK(yap::value(ref) == 1.0);
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/expression_function.cpp b/src/boost/libs/yap/test/expression_function.cpp
new file mode 100644
index 00000000..4819e0f3
--- /dev/null
+++ b/src/boost/libs/yap/test/expression_function.cpp
@@ -0,0 +1,70 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<int> number = {{42}};
+
+        auto fn = yap::make_expression_function(number);
+        auto fn_copy = fn;
+
+        BOOST_CHECK(fn() == 42);
+        BOOST_CHECK(fn_copy() == 42);
+
+        yap::value(number) = 21;
+
+        BOOST_CHECK(fn() == 21);
+        BOOST_CHECK(fn_copy() == 21);
+    }
+
+    {
+        term<int> number = {{42}};
+
+        auto fn = yap::make_expression_function(std::move(number));
+        auto fn_copy = fn;
+
+        BOOST_CHECK(fn() == 42);
+        BOOST_CHECK(fn_copy() == 42);
+
+        yap::value(number) = 21;
+
+        BOOST_CHECK(fn() == 42);
+        BOOST_CHECK(fn_copy() == 42);
+    }
+
+    {
+        term<std::unique_ptr<int>> number = {
+            {std::unique_ptr<int>(new int(42))}};
+
+        auto fn = yap::make_expression_function(std::move(number));
+
+        BOOST_CHECK(*fn() == 42);
+
+        auto fn_2 = std::move(fn);
+        BOOST_CHECK(*fn_2() == 42);
+
+        yap::value(number) = std::unique_ptr<int>(new int(21));
+
+        BOOST_CHECK(*fn_2() == 42);
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/fail_argument.cpp b/src/boost/libs/yap/test/fail_argument.cpp
new file mode 100644
index 00000000..69d2cc48
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_argument.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::argument(boost::yap::make_terminal(1), boost::hana::llong_c<0>);
+}
diff --git a/src/boost/libs/yap/test/fail_callable.cpp b/src/boost/libs/yap/test/fail_callable.cpp
new file mode 100644
index 00000000..ebdfe0a0
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_callable.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::callable(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_cond.cpp b/src/boost/libs/yap/test/fail_cond.cpp
new file mode 100644
index 00000000..73d2d6d4
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_cond.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::cond(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_else.cpp b/src/boost/libs/yap/test/fail_else.cpp
new file mode 100644
index 00000000..a4a65ae8
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_else.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::then(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_get.cpp b/src/boost/libs/yap/test/fail_get.cpp
new file mode 100644
index 00000000..c56f1efc
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_get.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::get(boost::yap::make_terminal(1), boost::hana::llong_c<1>);
+}
diff --git a/src/boost/libs/yap/test/fail_left.cpp b/src/boost/libs/yap/test/fail_left.cpp
new file mode 100644
index 00000000..0a6f1086
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_left.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::left(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_make_expression.cpp b/src/boost/libs/yap/test/fail_make_expression.cpp
new file mode 100644
index 00000000..3509656a
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_make_expression.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::make_expression<boost::yap::expr_kind::plus>(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_make_terminal.cpp b/src/boost/libs/yap/test/fail_make_terminal.cpp
new file mode 100644
index 00000000..59e49647
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_make_terminal.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::make_terminal(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_right.cpp b/src/boost/libs/yap/test/fail_right.cpp
new file mode 100644
index 00000000..2889df5e
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_right.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::right(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_then.cpp b/src/boost/libs/yap/test/fail_then.cpp
new file mode 100644
index 00000000..a4a65ae8
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_then.cpp
@@ -0,0 +1,12 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+int main()
+{
+    boost::yap::then(boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/fail_transform.cpp b/src/boost/libs/yap/test/fail_transform.cpp
new file mode 100644
index 00000000..54f5916b
--- /dev/null
+++ b/src/boost/libs/yap/test/fail_transform.cpp
@@ -0,0 +1,15 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+
+struct xform
+{};
+
+int main()
+{
+    boost::yap::transform(xform{}, boost::yap::make_terminal(1));
+}
diff --git a/src/boost/libs/yap/test/if_else.cpp b/src/boost/libs/yap/test/if_else.cpp
new file mode 100644
index 00000000..c3ed5204
--- /dev/null
+++ b/src/boost/libs/yap/test/if_else.cpp
@@ -0,0 +1,114 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using term_ref = boost::yap::expression_ref<boost::yap::expression, term<T> &>;
+
+template<typename T>
+using term_cref =
+    boost::yap::expression_ref<boost::yap::expression, term<T> const &>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+struct callable
+{
+    int operator()() { return 42; }
+};
+
+struct side_effect_callable_1
+{
+    int operator()()
+    {
+        *value_ = 1;
+        return 0;
+    }
+
+    int * value_;
+};
+
+struct side_effect_callable_2
+{
+    int operator()()
+    {
+        *value_ = 2;
+        return 0;
+    }
+
+    int * value_;
+};
+
+
+int test_main(int, char * [])
+{
+    {
+        int one = 0;
+        int two = 0;
+
+        auto true_nothrow_throw_expr = if_else(
+            term<bool>{{true}},
+            term<callable>{}(),
+            term<side_effect_callable_1>{{&one}}());
+
+        BOOST_CHECK(yap::evaluate(true_nothrow_throw_expr) == 42);
+        BOOST_CHECK(one == 0);
+        BOOST_CHECK(two == 0);
+    }
+
+    {
+        int one = 0;
+        int two = 0;
+
+        auto false_nothrow_throw_expr = if_else(
+            term<bool>{{false}},
+            term<callable>{}(),
+            term<side_effect_callable_1>{{&one}}());
+
+        BOOST_CHECK(yap::evaluate(false_nothrow_throw_expr) == 0);
+        BOOST_CHECK(one == 1);
+        BOOST_CHECK(two == 0);
+    }
+
+    {
+        int one = 0;
+        int two = 0;
+
+        auto true_throw1_throw2_expr = if_else(
+            term<bool>{{true}},
+            term<side_effect_callable_1>{{&one}}(),
+            term<side_effect_callable_2>{{&two}}());
+
+        BOOST_CHECK(yap::evaluate(true_throw1_throw2_expr) == 0);
+        BOOST_CHECK(one == 1);
+        BOOST_CHECK(two == 0);
+    }
+
+    {
+        int one = 0;
+        int two = 0;
+
+        auto false_throw1_throw2_expr = if_else(
+            term<bool>{{false}},
+            term<side_effect_callable_1>{{&one}}(),
+            term<side_effect_callable_2>{{&two}}());
+
+        BOOST_CHECK(yap::evaluate(false_throw1_throw2_expr) == 0);
+        BOOST_CHECK(one == 0);
+        BOOST_CHECK(two == 2);
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/lazy_vector_alloc_test.cpp b/src/boost/libs/yap/test/lazy_vector_alloc_test.cpp
new file mode 100644
index 00000000..e074247b
--- /dev/null
+++ b/src/boost/libs/yap/test/lazy_vector_alloc_test.cpp
@@ -0,0 +1,108 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <algorithm>
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+#include <boost/test/minimal.hpp>
+
+
+int allocations = 0;
+
+void * operator new(std::size_t size)
+{
+    ++allocations;
+    void * retval = malloc(size);
+    if (!retval)
+        throw std::bad_alloc();
+    return retval;
+}
+
+void operator delete(void * ptr) noexcept { free(ptr); }
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr;
+
+
+struct take_nth
+{
+    boost::yap::terminal<lazy_vector_expr, double> operator()(
+        boost::yap::terminal<lazy_vector_expr, std::vector<double>> const &
+            expr);
+
+    std::size_t n;
+};
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct lazy_vector_expr
+{
+    static const boost::yap::expr_kind kind = Kind;
+
+    Tuple elements;
+
+    auto operator[](std::size_t n) const
+    {
+        return boost::yap::evaluate(boost::yap::transform(*this, take_nth{n}));
+    }
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, lazy_vector_expr, lazy_vector_expr)
+BOOST_YAP_USER_BINARY_OPERATOR(minus, lazy_vector_expr, lazy_vector_expr)
+
+boost::yap::terminal<lazy_vector_expr, double> take_nth::operator()(
+    boost::yap::terminal<lazy_vector_expr, std::vector<double>> const & expr)
+{
+    double x = boost::yap::value(expr)[n];
+    return boost::yap::make_terminal<lazy_vector_expr, double>(std::move(x));
+}
+
+struct lazy_vector : lazy_vector_expr<
+                         boost::yap::expr_kind::terminal,
+                         boost::hana::tuple<std::vector<double>>>
+{
+    lazy_vector() {}
+
+    explicit lazy_vector(std::vector<double> && vec)
+    {
+        elements = boost::hana::tuple<std::vector<double>>(std::move(vec));
+    }
+
+    template<boost::yap::expr_kind Kind, typename Tuple>
+    lazy_vector & operator+=(lazy_vector_expr<Kind, Tuple> const & rhs)
+    {
+        std::vector<double> & this_vec = boost::yap::value(*this);
+        for (int i = 0, size = (int)this_vec.size(); i < size; ++i) {
+            this_vec[i] += rhs[i];
+        }
+        return *this;
+    }
+};
+
+
+int test_main(int, char * [])
+{
+    lazy_vector v1{std::vector<double>(4, 1.0)};
+    lazy_vector v2{std::vector<double>(4, 2.0)};
+    lazy_vector v3{std::vector<double>(4, 3.0)};
+
+    // Reset allocation count.  There should be none from this point on.
+    allocations = 0;
+
+    double d1 = (v2 + v3)[2];
+    std::cout << d1 << "\n";
+
+    v1 += v2 - v3;
+    std::cout << '{' << v1[0] << ',' << v1[1] << ',' << v1[2] << ',' << v1[3]
+              << '}' << "\n";
+
+    BOOST_CHECK(allocations == 0);
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/left.cpp b/src/boost/libs/yap/test/left.cpp
new file mode 100644
index 00000000..d6aa9d18
--- /dev/null
+++ b/src/boost/libs/yap/test/left.cpp
@@ -0,0 +1,318 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct user_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, user_expr, user_expr)
+
+template<typename T>
+using user_term = boost::yap::terminal<user_expr, T>;
+
+template<typename T>
+using user_ref = boost::yap::expression_ref<user_expr, T>;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<double> unity = {{1.0}};
+        using plus_expr_type = yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>;
+
+        {
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(std::move(plus_expr))),
+                              ref<term<double> &> &&>));
+        }
+
+        {
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(plus_expr)),
+                              ref<term<double> &> &>));
+        }
+
+        {
+            plus_expr_type const plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(plus_expr)),
+                              ref<term<double> &> const &>));
+        }
+
+        {
+            term<double> const unity = {{1.0}};
+            using plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> const &>, term<int>>>;
+
+            {
+                plus_expr_type plus_expr = unity + term<int>{{1}};
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr))),
+                                  ref<term<double> const &> &&>));
+            }
+
+            {
+                plus_expr_type plus_expr = unity + term<int>{{1}};
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr)),
+                                  ref<term<double> const &> &>));
+            }
+
+            {
+                plus_expr_type const plus_expr = unity + term<int>{{1}};
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr)),
+                                  ref<term<double> const &> const &>));
+            }
+        }
+
+        {
+            term<double> unity = {{1.0}};
+            using plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> &>, term<int>>>;
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+
+            using plus_plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<plus_expr_type &>, term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr_ref))),
+                                  ref<term<double> &> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  ref<term<double> &> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  ref<term<double> &> &>));
+            }
+        }
+
+        {
+            term<double> unity = {{1.0}};
+            using plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> &>, term<int>>>;
+            plus_expr_type const plus_expr = unity + term<int>{{1}};
+
+            using plus_plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<plus_expr_type const &>, term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr_ref))),
+                                  ref<term<double> &> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  ref<term<double> &> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  ref<term<double> &> const &>));
+            }
+        }
+    }
+
+    {
+        user_term<double> unity = {{1.0}};
+        using plus_expr_type = user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+
+        {
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(std::move(plus_expr))),
+                              user_ref<user_term<double> &> &&>));
+        }
+
+        {
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(plus_expr)),
+                              user_ref<user_term<double> &> &>));
+        }
+
+        {
+            plus_expr_type const plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::left(plus_expr)),
+                              user_ref<user_term<double> &> const &>));
+        }
+
+        {
+            user_term<double> const unity = {{1.0}};
+            using plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> const &>, user_term<int>>>;
+
+            {
+                plus_expr_type plus_expr = unity + user_term<int>{{1}};
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr))),
+                                  user_ref<user_term<double> const &> &&>));
+            }
+
+            {
+                plus_expr_type plus_expr = unity + user_term<int>{{1}};
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr)),
+                                  user_ref<user_term<double> const &> &>));
+            }
+
+            {
+                plus_expr_type const plus_expr = unity + user_term<int>{{1}};
+                BOOST_MPL_ASSERT(
+                    (std::is_same<
+                        decltype(yap::left(plus_expr)),
+                        user_ref<user_term<double> const &> const &>));
+            }
+        }
+
+        {
+            user_term<double> unity = {{1.0}};
+            using plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+
+            using plus_plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<plus_expr_type &>, user_term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr_ref))),
+                                  user_ref<user_term<double> &> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  user_ref<user_term<double> &> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  user_ref<user_term<double> &> &>));
+            }
+        }
+
+        {
+            user_term<double> unity = {{1.0}};
+            using plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+            plus_expr_type const plus_expr = unity + user_term<int>{{1}};
+
+            using plus_plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<plus_expr_type const &>, user_term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(std::move(plus_expr_ref))),
+                                  user_ref<user_term<double> &> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  user_ref<user_term<double> &> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::left(plus_expr_ref)),
+                                  user_ref<user_term<double> &> const &>));
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/operators_unary.cpp b/src/boost/libs/yap/test/operators_unary.cpp
new file mode 100644
index 00000000..6372f3d3
--- /dev/null
+++ b/src/boost/libs/yap/test/operators_unary.cpp
@@ -0,0 +1,174 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using term_ref = boost::yap::expression_ref<boost::yap::expression, term<T> &>;
+
+template<typename T>
+using term_cref =
+    boost::yap::expression_ref<boost::yap::expression, term<T> const &>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<uint32_t> x{{2u}};
+        term<uint32_t> const cx{{3u}};
+
+        {
+            yap::expression<
+                yap::expr_kind::unary_plus,
+                bh::tuple<term<uint32_t>>>
+                term_expr = +term<uint32_t>{{1u}};
+            yap::expression<
+                yap::expr_kind::unary_plus,
+                bh::tuple<term_ref<uint32_t>>>
+                term_ref_expr = +x;
+            yap::expression<
+                yap::expr_kind::unary_plus,
+                bh::tuple<term_cref<uint32_t>>>
+                term_const_ref_expr = +cx;
+
+            BOOST_CHECK(evaluate(term_expr) == 1u);
+            BOOST_CHECK(evaluate(term_ref_expr) == 2u);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == 3u);
+        }
+
+        {
+            yap::expression<yap::expr_kind::negate, bh::tuple<term<uint32_t>>>
+                term_expr = -term<uint32_t>{{1u}};
+            yap::expression<
+                yap::expr_kind::negate,
+                bh::tuple<term_ref<uint32_t>>>
+                term_ref_expr = -x;
+            yap::expression<
+                yap::expr_kind::negate,
+                bh::tuple<term_cref<uint32_t>>>
+                term_const_ref_expr = -cx;
+
+            BOOST_CHECK(evaluate(term_expr) == 0u - 1u);
+            BOOST_CHECK(evaluate(term_ref_expr) == 0u - 2u);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == 0u - 3u);
+        }
+
+        {
+            yap::expression<
+                yap::expr_kind::complement,
+                bh::tuple<term<uint32_t>>>
+                term_expr = ~term<uint32_t>{{1u}};
+            yap::expression<
+                yap::expr_kind::complement,
+                bh::tuple<term_ref<uint32_t>>>
+                term_ref_expr = ~x;
+            yap::expression<
+                yap::expr_kind::complement,
+                bh::tuple<term_cref<uint32_t>>>
+                term_const_ref_expr = ~cx;
+
+            BOOST_CHECK(evaluate(term_expr) == 0xfffffffe);
+            BOOST_CHECK(evaluate(term_ref_expr) == 0xfffffffd);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == 0xfffffffc);
+        }
+
+        {
+            yap::expression<
+                yap::expr_kind::logical_not,
+                bh::tuple<term<uint32_t>>>
+                term_expr = !term<uint32_t>{{1u}};
+            yap::expression<
+                yap::expr_kind::logical_not,
+                bh::tuple<term_ref<uint32_t>>>
+                term_ref_expr = !x;
+            yap::expression<
+                yap::expr_kind::logical_not,
+                bh::tuple<term_cref<uint32_t>>>
+                term_const_ref_expr = !cx;
+
+            BOOST_CHECK(evaluate(term_expr) == false);
+            BOOST_CHECK(evaluate(term_ref_expr) == false);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == false);
+        }
+
+        {
+            yap::expression<yap::expr_kind::pre_inc, bh::tuple<term<uint32_t>>>
+                term_expr = ++term<uint32_t>{{1u}};
+            yap::expression<
+                yap::expr_kind::pre_inc,
+                bh::tuple<term_ref<uint32_t>>>
+                term_ref_expr = ++x;
+            yap::expression<
+                yap::expr_kind::pre_inc,
+                bh::tuple<term_cref<uint32_t>>>
+                term_const_ref_expr = ++cx;
+            (void)term_const_ref_expr;
+
+            BOOST_CHECK(evaluate(term_expr) == 2u);
+            BOOST_CHECK(evaluate(term_ref_expr) == 3u);
+        }
+    }
+
+    {
+        {
+            uint32_t i = 1, j = 2, k = 3;
+            term<uint32_t &> x{{j}};
+            term<uint32_t &> const cx{{k}};
+
+            yap::expression<
+                yap::expr_kind::address_of,
+                bh::tuple<term<uint32_t &>>>
+                term_expr = &term<uint32_t &>{{i}};
+            yap::expression<
+                yap::expr_kind::address_of,
+                bh::tuple<term_ref<uint32_t &>>>
+                term_ref_expr = &x;
+            yap::expression<
+                yap::expr_kind::address_of,
+                bh::tuple<term_cref<uint32_t &>>>
+                term_const_ref_expr = &cx;
+
+            BOOST_CHECK(evaluate(term_expr) == &i);
+            BOOST_CHECK(evaluate(term_ref_expr) == &j);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == &k);
+        }
+
+        {
+            uint32_t i = 1, j = 2, k = 3;
+            term<uint32_t *> x{{&j}};
+            term<uint32_t *> const cx{{&k}};
+
+            yap::expression<
+                yap::expr_kind::dereference,
+                bh::tuple<term<uint32_t *>>>
+                term_expr = *term<uint32_t *>{{&i}};
+            yap::expression<
+                yap::expr_kind::dereference,
+                bh::tuple<term_ref<uint32_t *>>>
+                term_ref_expr = *x;
+            yap::expression<
+                yap::expr_kind::dereference,
+                bh::tuple<term_cref<uint32_t *>>>
+                term_const_ref_expr = *cx;
+
+            BOOST_CHECK(evaluate(term_expr) == i);
+            BOOST_CHECK(evaluate(term_ref_expr) == j);
+            BOOST_CHECK(evaluate(term_const_ref_expr) == k);
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/placeholder_eval.cpp b/src/boost/libs/yap/test/placeholder_eval.cpp
new file mode 100644
index 00000000..76f9c378
--- /dev/null
+++ b/src/boost/libs/yap/test/placeholder_eval.cpp
@@ -0,0 +1,65 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<long long I>
+using place_term =
+    boost::yap::terminal<boost::yap::expression, boost::yap::placeholder<I>>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+int test_main(int, char * [])
+{
+    {
+        using namespace boost::yap::literals;
+
+        place_term<3> p3 = 3_p;
+        int i_ = 42;
+        term<int> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<place_term<3> &>, term<int>>>
+            expr = p3 + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<place_term<3> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<place_term<3> &>, term<int>>>>>
+            unevaluated_expr = p3 + std::move(expr);
+
+        {
+            double result = evaluate(p3, 5, 6, 7);
+            BOOST_CHECK(result == 7);
+        }
+
+        {
+            double result = evaluate(expr, std::string("15"), 3, 1);
+            BOOST_CHECK(result == 43);
+        }
+
+        {
+            double result = evaluate(unevaluated_expr, std::string("15"), 2, 3);
+            BOOST_CHECK(result == 48);
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/print.cpp b/src/boost/libs/yap/test/print.cpp
new file mode 100644
index 00000000..106dcea4
--- /dev/null
+++ b/src/boost/libs/yap/test/print.cpp
@@ -0,0 +1,1595 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+#include <boost/yap/print.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+#include <regex>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct user_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, user_expr, user_expr)
+
+template<typename T>
+using user_term = boost::yap::terminal<user_expr, T>;
+
+template<typename T>
+using user_ref = boost::yap::expression_ref<user_expr, T>;
+
+struct thing
+{};
+
+std::string fix_tti(std::string s)
+{
+    // msvc: remove struct/class prefixes
+    static const std::regex estruct("(struct|class) ");
+    s = std::regex_replace(s, estruct, "");
+
+    // gcc/clang: strip integral literals suffixes
+    static const std::regex eint("(\\d)u?l{0,2}");
+    s = std::regex_replace(s, eint, "$1");
+
+    return s;
+}
+
+int test_main(int, char * [])
+{
+    {
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::terminal) == std::string("term"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::unary_plus) == std::string("+"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::negate) == std::string("-"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::dereference) == std::string("*"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::complement) == std::string("~"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::address_of) == std::string("&"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::logical_not) == std::string("!"));
+
+        BOOST_CHECK(yap::op_string(yap::expr_kind::pre_inc) == std::string("++"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::pre_dec) == std::string("--"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::post_inc) == std::string("++(int)"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::post_dec) == std::string("--(int)"));
+
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::shift_left) == std::string("<<"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::shift_right) == std::string(">>"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::multiplies) == std::string("*"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::divides) == std::string("/"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::modulus) == std::string("%"));
+
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::multiplies_assign) ==
+            std::string("*="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::divides_assign) ==
+            std::string("/="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::modulus_assign) ==
+            std::string("%="));
+
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::plus_assign) == std::string("+="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::minus_assign) == std::string("-="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::bitwise_and_assign) ==
+            std::string("&="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::bitwise_or_assign) ==
+            std::string("|="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::bitwise_xor_assign) ==
+            std::string("^="));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind::subscript) == std::string("[]"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::if_else) == std::string("?:"));
+        BOOST_CHECK(yap::op_string(yap::expr_kind::call) == std::string("()"));
+        BOOST_CHECK(
+            yap::op_string(yap::expr_kind(-1)) ==
+            std::string("** ERROR: UNKNOWN OPERATOR! **"));
+    }
+
+    {
+        user_term<double> unity{1.0};
+        int i_ = 42;
+        user_term<int &&> i{std::move(i_)};
+        user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<user_ref<user_term<double> &>, user_term<int &&>>>
+            expr = unity + std::move(i);
+        user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<
+                user_ref<user_term<double> &>,
+                user_expr<
+                    yap::expr_kind::plus,
+                    bh::tuple<
+                        user_ref<user_term<double> &>,
+                        user_term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    expr<+>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        user_term<thing> a_thing{bh::make_tuple(thing{})};
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        user_term<double> const const_unity{1.0};
+        user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<
+                user_ref<user_term<double> &>,
+                user_ref<user_term<double> const &>>>
+            nonconst_plus_const = unity + const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_plus_const);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        auto nonconst_plus_nonconst_plus_const = unity + nonconst_plus_const;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_plus_nonconst_plus_const);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    expr<+> &
+        term<double>[=1] &
+        term<double>[=1] const &
+)");
+        }
+
+        auto const const_nonconst_plus_const = nonconst_plus_const;
+        auto nonconst_plus_nonconst_plus_const_2 =
+            unity + const_nonconst_plus_const;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_plus_nonconst_plus_const_2);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    expr<+> const &
+        term<double>[=1] &
+        term<double>[=1] const &
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity + std::move(i);
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity + std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    expr<+>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_plus_const = unity + const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_plus_const);
+            BOOST_CHECK(oss.str() == R"(expr<+>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::minus,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity - std::move(i);
+        yap::expression<
+            yap::expr_kind::minus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::minus,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity - std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<->
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<->
+    term<double>[=1] &
+    expr<->
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::minus,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_minus_const = unity - const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_minus_const);
+            BOOST_CHECK(oss.str() == R"(expr<->
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::less,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity < std::move(i);
+        yap::expression<
+            yap::expr_kind::less,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::less,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity < std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<<>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<<>
+    term<double>[=1] &
+    expr<<>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::less,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_less_const = unity < const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_less_const);
+            BOOST_CHECK(oss.str() == R"(expr<<>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::greater,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity > std::move(i);
+        yap::expression<
+            yap::expr_kind::greater,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::greater,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity > std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<>>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<>>
+    term<double>[=1] &
+    expr<>>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::greater,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_greater_const = unity > const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_greater_const);
+            BOOST_CHECK(oss.str() == R"(expr<>>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::less_equal,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity <= std::move(i);
+        yap::expression<
+            yap::expr_kind::less_equal,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::less_equal,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity <= std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<<=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<<=>
+    term<double>[=1] &
+    expr<<=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::less_equal,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_less_equal_const = unity <= const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_less_equal_const);
+            BOOST_CHECK(oss.str() == R"(expr<<=>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::greater_equal,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity >= std::move(i);
+        yap::expression<
+            yap::expr_kind::greater_equal,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::greater_equal,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity >= std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<>=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<>=>
+    term<double>[=1] &
+    expr<>=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::greater_equal,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_greater_equal_const = unity >= const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_greater_equal_const);
+            BOOST_CHECK(oss.str() == R"(expr<>=>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::equal_to,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity == std::move(i);
+        yap::expression<
+            yap::expr_kind::equal_to,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::equal_to,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity == std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<==>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<==>
+    term<double>[=1] &
+    expr<==>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::equal_to,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_equal_to_const = unity == const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_equal_to_const);
+            BOOST_CHECK(oss.str() == R"(expr<==>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::not_equal_to,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity != std::move(i);
+        yap::expression<
+            yap::expr_kind::not_equal_to,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::not_equal_to,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity != std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<!=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<!=>
+    term<double>[=1] &
+    expr<!=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::not_equal_to,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_not_equal_to_const = unity != const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_not_equal_to_const);
+            BOOST_CHECK(oss.str() == R"(expr<!=>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::logical_or,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity || std::move(i);
+        yap::expression<
+            yap::expr_kind::logical_or,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::logical_or,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity || std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<||>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<||>
+    term<double>[=1] &
+    expr<||>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::logical_or,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_logical_or_const = unity || const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_logical_or_const);
+            BOOST_CHECK(oss.str() == R"(expr<||>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::logical_and,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity && std::move(i);
+        yap::expression<
+            yap::expr_kind::logical_and,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::logical_and,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity && std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<&&>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<&&>
+    term<double>[=1] &
+    expr<&&>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::logical_and,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_logical_and_const = unity && const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_logical_and_const);
+            BOOST_CHECK(oss.str() == R"(expr<&&>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::bitwise_and,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity & std::move(i);
+        yap::expression<
+            yap::expr_kind::bitwise_and,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::bitwise_and,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity & std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<&>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<&>
+    term<double>[=1] &
+    expr<&>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::bitwise_and,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_bitwise_and_const = unity & const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_bitwise_and_const);
+            BOOST_CHECK(oss.str() == R"(expr<&>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::bitwise_or,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity | std::move(i);
+        yap::expression<
+            yap::expr_kind::bitwise_or,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::bitwise_or,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity | std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<|>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<|>
+    term<double>[=1] &
+    expr<|>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::bitwise_or,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_bitwise_or_const = unity | const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_bitwise_or_const);
+            BOOST_CHECK(oss.str() == R"(expr<|>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::bitwise_xor,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity ^ std::move(i);
+        yap::expression<
+            yap::expr_kind::bitwise_xor,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::bitwise_xor,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity ^ std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<^>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<^>
+    term<double>[=1] &
+    expr<^>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::bitwise_xor,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_bitwise_xor_const = unity ^ const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_bitwise_xor_const);
+            BOOST_CHECK(oss.str() == R"(expr<^>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::comma,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = (unity, std::move(i));
+        yap::expression<
+            yap::expr_kind::comma,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::comma,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = (unity, std::move(expr));
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<,>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<,>
+    term<double>[=1] &
+    expr<,>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::comma,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_comma_const = (unity, const_unity);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_comma_const);
+            BOOST_CHECK(oss.str() == R"(expr<,>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::mem_ptr,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity->*std::move(i);
+        yap::expression<
+            yap::expr_kind::mem_ptr,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::mem_ptr,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity->*std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<->*>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<->*>
+    term<double>[=1] &
+    expr<->*>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::mem_ptr,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_mem_ptr_const = unity->*const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_mem_ptr_const);
+            BOOST_CHECK(oss.str() == R"(expr<->*>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::assign,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity = std::move(i);
+        yap::expression<
+            yap::expr_kind::assign,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::assign,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity = std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<=>
+    term<double>[=1] &
+    expr<=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::shift_left_assign,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity <<= std::move(i);
+        yap::expression<
+            yap::expr_kind::shift_left_assign,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::shift_left_assign,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity <<= std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<<<=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<<<=>
+    term<double>[=1] &
+    expr<<<=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::shift_left_assign,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_shift_left_assign_const = unity <<= const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_shift_left_assign_const);
+            BOOST_CHECK(oss.str() == R"(expr<<<=>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        int i_ = 42;
+        term<int &&> i{std::move(i_)};
+        yap::expression<
+            yap::expr_kind::shift_right_assign,
+            bh::tuple<ref<term<double> &>, term<int &&>>>
+            expr = unity >>= std::move(i);
+        yap::expression<
+            yap::expr_kind::shift_right_assign,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::shift_right_assign,
+                    bh::tuple<ref<term<double> &>, term<int &&>>>>>
+            unevaluated_expr = unity >>= std::move(expr);
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unity);
+            BOOST_CHECK(oss.str() == R"(term<double>[=1]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, expr);
+            BOOST_CHECK(oss.str() == R"(expr<>>=>
+    term<double>[=1] &
+    term<int &&>[=42]
+)");
+        }
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, unevaluated_expr);
+            BOOST_CHECK(oss.str() == R"(expr<>>=>
+    term<double>[=1] &
+    expr<>>=>
+        term<double>[=1] &
+        term<int &&>[=42]
+)");
+        }
+
+        term<thing> a_thing(thing{});
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, a_thing);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<thing>[=<<unprintable-value>>]
+)");
+        }
+
+        term<double> const const_unity{1.0};
+        yap::expression<
+            yap::expr_kind::shift_right_assign,
+            bh::tuple<ref<term<double> &>, ref<term<double> const &>>>
+            nonconst_shift_right_assign_const = unity >>= const_unity;
+
+        {
+            std::ostringstream oss;
+            yap::print(oss, nonconst_shift_right_assign_const);
+            BOOST_CHECK(oss.str() == R"(expr<>>=>
+    term<double>[=1] &
+    term<double>[=1] const &
+)");
+        }
+
+        {
+            using namespace yap::literals;
+            std::ostringstream oss;
+            yap::print(oss, 1_p);
+            BOOST_CHECK(fix_tti(oss.str()) == R"(term<boost::yap::placeholder<1>>[=1]
+)");
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/reference_returns.cpp b/src/boost/libs/yap/test/reference_returns.cpp
new file mode 100644
index 00000000..e03e9a3c
--- /dev/null
+++ b/src/boost/libs/yap/test/reference_returns.cpp
@@ -0,0 +1,89 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+
+namespace reference_returning {
+
+    struct number
+    {
+        double value;
+    };
+
+    number a_result{3.0};
+    number const the_result{13.0};
+
+    number const & operator+(number a, number b) { return the_result; }
+
+    number & operator-(number a, number b) { return a_result; }
+}
+
+int test_main(int, char * [])
+{
+    {
+        term<reference_returning::number> unity = {{1.0}};
+        auto plus_expr = unity + reference_returning::number{1.0};
+
+        {
+            reference_returning::number const & n = evaluate(plus_expr);
+            BOOST_CHECK(&n == &reference_returning::the_result);
+        }
+
+        using plus_eval_type = decltype(evaluate(plus_expr));
+        BOOST_MPL_ASSERT((std::is_same<
+                          plus_eval_type,
+                          reference_returning::number const &>));
+
+        auto minus_expr = unity - reference_returning::number{1.0};
+
+        {
+            reference_returning::number & n = evaluate(minus_expr);
+            BOOST_CHECK(&n == &reference_returning::a_result);
+        }
+
+        using minus_eval_type = decltype(evaluate(minus_expr));
+        BOOST_MPL_ASSERT((std::is_same<
+                          minus_eval_type,
+                          reference_returning::number &>));
+
+        using namespace yap::literals;
+
+        {
+            reference_returning::number & n =
+                evaluate(1_p, reference_returning::a_result);
+            BOOST_CHECK(&n == &reference_returning::a_result);
+        }
+
+        using a_eval_type = decltype(evaluate(1_p, reference_returning::a_result));
+        BOOST_MPL_ASSERT(
+            (std::is_same<
+                a_eval_type,
+                reference_returning::number &>));
+
+        {
+            reference_returning::number const & n =
+                evaluate(1_p, reference_returning::the_result);
+            BOOST_CHECK(&n == &reference_returning::the_result);
+        }
+
+        using the_eval_type = decltype(evaluate(1_p, reference_returning::the_result));
+        BOOST_MPL_ASSERT(
+            (std::is_same<
+                the_eval_type,
+                reference_returning::number const &>));
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/right.cpp b/src/boost/libs/yap/test/right.cpp
new file mode 100644
index 00000000..6a868423
--- /dev/null
+++ b/src/boost/libs/yap/test/right.cpp
@@ -0,0 +1,264 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct user_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, user_expr, user_expr)
+
+template<typename T>
+using user_term = boost::yap::terminal<user_expr, T>;
+
+template<typename T>
+using user_ref = boost::yap::expression_ref<user_expr, T>;
+
+
+int test_main(int, char * [])
+{
+    {
+        term<double> unity = {{1.0}};
+        using plus_expr_type = yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>;
+
+        {
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::right(std::move(plus_expr))),
+                              term<int> &&>));
+        }
+
+        {
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::right(plus_expr)), term<int> &>));
+        }
+
+        {
+            plus_expr_type const plus_expr = unity + term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::right(plus_expr)),
+                              term<int> const &>));
+        }
+
+        {
+            term<double> unity = {{1.0}};
+            using plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> &>, term<int>>>;
+            plus_expr_type plus_expr = unity + term<int>{{1}};
+
+            using plus_plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<plus_expr_type &>, term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<
+                        decltype(yap::right(std::move(plus_expr_ref))),
+                        term<int> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  term<int> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  term<int> &>));
+            }
+        }
+
+        {
+            term<double> unity = {{1.0}};
+            using plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> &>, term<int>>>;
+            plus_expr_type const plus_expr = unity + term<int>{{1}};
+
+            using plus_plus_expr_type = yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<plus_expr_type const &>, term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<
+                        decltype(yap::right(std::move(plus_expr_ref))),
+                        term<int> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  term<int> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr = plus_expr + term<int>{{1}};
+                ref<plus_expr_type const &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  term<int> const &>));
+            }
+        }
+    }
+
+    {
+        user_term<double> unity = {{1.0}};
+        using plus_expr_type = user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+
+        {
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::right(std::move(plus_expr))),
+                              user_term<int> &&>));
+        }
+
+        {
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::right(plus_expr)),
+                              user_term<int> &>));
+        }
+
+        {
+            plus_expr_type const plus_expr = unity + user_term<int>{{1}};
+            BOOST_MPL_ASSERT((std::is_same<
+                              decltype(yap::right(plus_expr)),
+                              user_term<int> const &>));
+        }
+
+        {
+            user_term<double> unity = {{1.0}};
+            using plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+            plus_expr_type plus_expr = unity + user_term<int>{{1}};
+
+            using plus_plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<plus_expr_type &>, user_term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<
+                        decltype(yap::right(std::move(plus_expr_ref))),
+                        user_term<int> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  user_term<int> &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  user_term<int> &>));
+            }
+        }
+
+        {
+            user_term<double> unity = {{1.0}};
+            using plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+            plus_expr_type const plus_expr = unity + user_term<int>{{1}};
+
+            using plus_plus_expr_type = user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<plus_expr_type const &>, user_term<int>>>;
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<
+                        decltype(yap::right(std::move(plus_expr_ref))),
+                        user_term<int> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  user_term<int> const &>));
+            }
+
+            {
+                plus_plus_expr_type plus_plus_expr =
+                    plus_expr + user_term<int>{{1}};
+                user_ref<plus_expr_type const &> const plus_expr_ref =
+                    bh::front(plus_plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::right(plus_expr_ref)),
+                                  user_term<int> const &>));
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/transform.cpp b/src/boost/libs/yap/test/transform.cpp
new file mode 100644
index 00000000..edca1670
--- /dev/null
+++ b/src/boost/libs/yap/test/transform.cpp
@@ -0,0 +1,78 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/yap.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+#include <sstream>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::minimal_expr, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+struct iota_terminal_transform
+{
+    template<typename T>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T && t)
+    {
+        return boost::yap::make_terminal(index_++);
+    }
+
+    template<typename CallableExpr, typename... Arg>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::call>,
+                    CallableExpr callable, Arg &&... arg)
+    {
+        return boost::yap::make_expression<boost::yap::expr_kind::call>(
+            callable, boost::yap::transform(arg, *this)...);
+    }
+
+    int index_;
+};
+
+struct plus_expr_t
+{
+    static yap::expr_kind const kind = yap::expr_kind::plus;
+
+    bh::tuple<term<int>, term<int>> elements;
+};
+
+int test_main(int, char * [])
+{
+    // Each node instantiated from from yap::expression.
+    {
+        auto plus_expr = yap::terminal<yap::expression, int>{{5}} + 6;
+
+        BOOST_CHECK(yap::evaluate(plus_expr) == 11);
+
+        BOOST_CHECK(
+            yap::evaluate(
+                yap::transform(plus_expr, iota_terminal_transform{0})) == 1);
+    }
+
+    // Each node instantiated from from yap::minimal_expr.
+    {
+        yap::minimal_expr<yap::expr_kind::plus, bh::tuple<term<int>, term<int>>>
+            plus_expr;
+
+        yap::evaluate(yap::transform(plus_expr, iota_terminal_transform{0}), 1);
+    }
+
+    // Leaves are instantiated from from yap::minimal_expr; nonterminal
+    // expr_kind::plus does not even come from a template.
+    {
+        plus_expr_t plus_expr;
+
+        yap::evaluate(yap::transform(plus_expr, iota_terminal_transform{0}), 1);
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/user_expression_transform_1.cpp b/src/boost/libs/yap/test/user_expression_transform_1.cpp
new file mode 100644
index 00000000..b58b6e25
--- /dev/null
+++ b/src/boost/libs/yap/test/user_expression_transform_1.cpp
@@ -0,0 +1,948 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+namespace user {
+
+    struct number
+    {
+        double value;
+
+        friend number operator+(number lhs, number rhs)
+        {
+            return number{lhs.value + rhs.value};
+        }
+
+        friend number operator-(number lhs, number rhs)
+        {
+            return number{lhs.value - rhs.value};
+        }
+
+        friend number operator*(number lhs, number rhs)
+        {
+            return number{lhs.value * rhs.value};
+        }
+
+        friend number operator-(number n) { return number{-n.value}; }
+
+        friend bool operator<(number lhs, double rhs)
+        {
+            return lhs.value < rhs;
+        }
+
+        friend bool operator<(double lhs, number rhs)
+        {
+            return lhs < rhs.value;
+        }
+    };
+
+    number naxpy(number a, number x, number y)
+    {
+        return number{a.value * x.value + y.value + 10.0};
+    }
+
+    struct empty_xform
+    {};
+
+    struct eval_xform_tag
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return n;
+        }
+    };
+
+    struct eval_xform_expr
+    {
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            return ::boost::yap::value(expr);
+        }
+    };
+
+    struct eval_xform_both
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return n;
+        }
+
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return ::boost::yap::value(expr);
+        }
+    };
+
+    struct plus_to_minus_xform_tag
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            user::number const & lhs,
+            user::number const & rhs)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                term<user::number>{lhs}, term<user::number>{rhs});
+        }
+    };
+
+    struct plus_to_minus_xform_expr
+    {
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                ::boost::yap::left(expr), ::boost::yap::right(expr));
+        }
+    };
+
+    struct plus_to_minus_xform_both
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            user::number const & lhs,
+            user::number const & rhs)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                term<user::number>{lhs}, term<user::number>{rhs});
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return yap::make_expression<yap::expr_kind::minus>(
+                ::boost::yap::left(expr), ::boost::yap::right(expr));
+        }
+    };
+
+    struct term_nonterm_xform_tag
+    {
+        auto operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return yap::make_terminal(n * user::number{2.0});
+        }
+
+        auto operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            user::number const & lhs,
+            user::number const & rhs)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                yap::transform(::boost::yap::make_terminal(lhs), *this),
+                yap::transform(::boost::yap::make_terminal(rhs), *this));
+        }
+    };
+
+    struct term_nonterm_xform_expr
+    {
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            return yap::make_terminal(
+                ::boost::yap::value(expr) * user::number{2.0});
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                yap::transform(::boost::yap::left(expr), *this),
+                yap::transform(::boost::yap::right(expr), *this));
+        }
+    };
+
+    struct term_nonterm_xform_both
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return yap::make_terminal(n * user::number{2.0});
+        }
+
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            return yap::make_terminal(
+                ::boost::yap::value(expr) * user::number{2.0});
+        }
+
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            user::number const & lhs,
+            user::number const & rhs)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                yap::transform(::boost::yap::make_terminal(lhs), *this),
+                yap::transform(::boost::yap::make_terminal(rhs), *this));
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            return yap::make_expression<yap::expr_kind::minus>(
+                yap::transform(::boost::yap::left(expr), *this),
+                yap::transform(::boost::yap::right(expr), *this));
+        }
+    };
+
+    struct eval_term_nonterm_xform_tag
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return n * user::number{2.0};
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            Expr1 const & lhs,
+            Expr2 const & rhs)
+        {
+            return boost::yap::transform(::boost::yap::as_expr(lhs), *this) -
+                   boost::yap::transform(::boost::yap::as_expr(rhs), *this);
+        }
+    };
+
+    struct eval_term_nonterm_xform_expr
+    {
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            return ::boost::yap::value(expr) * user::number{2.0};
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            return boost::yap::transform(::boost::yap::left(expr), *this) -
+                   boost::yap::transform(::boost::yap::right(expr), *this);
+        }
+    };
+
+    struct eval_term_nonterm_xform_both
+    {
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::terminal>, user::number const & n)
+        {
+            return n * user::number{2.0};
+        }
+
+        decltype(auto) operator()(term<user::number> const & expr)
+        {
+            return ::boost::yap::value(expr) * user::number{2.0};
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::plus>,
+            Expr1 const & lhs,
+            Expr2 const & rhs)
+        {
+            return boost::yap::transform(::boost::yap::as_expr(lhs), *this) -
+                   boost::yap::transform(::boost::yap::as_expr(rhs), *this);
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            return boost::yap::transform(::boost::yap::left(expr), *this) -
+                   boost::yap::transform(::boost::yap::right(expr), *this);
+        }
+    };
+
+    decltype(auto)
+    naxpy_eager_nontemplate_xform(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<
+                                      yap::expression<
+                                          yap::expr_kind::multiplies,
+                                          bh::tuple<
+                                              ref<term<user::number> &>,
+                                              ref<term<user::number> &>>>,
+                                      ref<term<user::number> &>>> const & expr)
+    {
+        auto a = evaluate(expr.left().left());
+        auto x = evaluate(expr.left().right());
+        auto y = evaluate(expr.right());
+        return yap::make_terminal(naxpy(a, x, y));
+    }
+
+    decltype(auto)
+    naxpy_lazy_nontemplate_xform(yap::expression<
+                                 yap::expr_kind::plus,
+                                 bh::tuple<
+                                     yap::expression<
+                                         yap::expr_kind::multiplies,
+                                         bh::tuple<
+                                             ref<term<user::number> &>,
+                                             ref<term<user::number> &>>>,
+                                     ref<term<user::number> &>>> const & expr)
+    {
+        decltype(auto) a = expr.left().left().value();
+        decltype(auto) x = expr.left().right().value();
+        decltype(auto) y = expr.right().value();
+        return yap::make_terminal(naxpy)(a, x, y);
+    }
+
+    struct naxpy_xform
+    {
+        template<typename Expr1, typename Expr2, typename Expr3>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<
+                                      yap::expression<
+                                          yap::expr_kind::multiplies,
+                                          bh::tuple<Expr1, Expr2>>,
+                                      Expr3>> const & expr)
+        {
+            return yap::make_terminal(naxpy)(
+                transform(expr.left().left(), naxpy_xform{}),
+                transform(expr.left().right(), naxpy_xform{}),
+                transform(expr.right(), naxpy_xform{}));
+        }
+    };
+
+
+    // unary transforms
+
+    struct disable_negate_xform_tag
+    {
+        auto
+        operator()(yap::expr_tag<yap::expr_kind::negate>, user::number value)
+        {
+            return yap::make_terminal(std::move(value));
+        }
+
+        template<typename Expr>
+        auto
+        operator()(yap::expr_tag<yap::expr_kind::negate>, Expr const & expr)
+        {
+            return expr;
+        }
+    };
+
+    struct disable_negate_xform_expr
+    {
+        template<typename Expr>
+        decltype(auto) operator()(
+            yap::expression<yap::expr_kind::negate, bh::tuple<Expr>> const &
+                expr)
+        {
+            return ::boost::yap::value(expr);
+        }
+    };
+
+    struct disable_negate_xform_both
+    {
+        decltype(auto)
+        operator()(yap::expr_tag<yap::expr_kind::negate>, user::number value)
+        {
+            return yap::make_terminal(std::move(value));
+        }
+
+        template<typename Expr>
+        decltype(auto)
+        operator()(yap::expr_tag<yap::expr_kind::negate>, Expr const & expr)
+        {
+            return expr;
+        }
+
+        template<typename Expr>
+        decltype(auto) operator()(
+            yap::expression<yap::expr_kind::negate, bh::tuple<Expr>> const &
+                expr)
+        {
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return ::boost::yap::value(expr);
+        }
+    };
+
+
+    // ternary transforms
+
+    //[ tag_xform
+    struct ternary_to_else_xform_tag
+    {
+        template<typename Expr>
+        decltype(auto) operator()(
+            boost::yap::expr_tag<yap::expr_kind::if_else>,
+            Expr const & cond,
+            user::number then,
+            user::number else_)
+        {
+            return boost::yap::make_terminal(std::move(else_));
+        }
+    };
+    //]
+
+    //[ expr_xform
+    struct ternary_to_else_xform_expr
+    {
+        template<typename Cond, typename Then, typename Else>
+        decltype(auto)
+        operator()(boost::yap::expression<
+                   boost::yap::expr_kind::if_else,
+                   boost::hana::tuple<Cond, Then, Else>> const & expr)
+        {
+            return ::boost::yap::else_(expr);
+        }
+    };
+    //]
+
+    struct ternary_to_else_xform_both
+    {
+        template<typename Expr>
+        decltype(auto) operator()(
+            yap::expr_tag<yap::expr_kind::if_else>,
+            Expr const & cond,
+            user::number then,
+            user::number else_)
+        {
+            return yap::make_terminal(std::move(else_));
+        }
+
+        template<typename Cond, typename Then, typename Else>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::if_else,
+                                  bh::tuple<Cond, Then, Else>> const & expr)
+        {
+            throw std::logic_error("Oops!  Picked the wrong overload!");
+            return ::boost::yap::else_(expr);
+        }
+    };
+}
+
+auto double_to_float(term<double> expr)
+{
+    return term<float>{(float)expr.value()};
+}
+
+auto check_unique_ptrs_equal_7(term<std::unique_ptr<int>> && expr)
+{
+    using namespace boost::hana::literals;
+    BOOST_CHECK(*expr.elements[0_c] == 7);
+    return std::move(expr);
+}
+
+int test_main(int, char * [])
+{
+    {
+        term<user::number> a{{1.0}};
+        term<user::number> x{{42.0}};
+        term<user::number> y{{3.0}};
+
+        {
+            auto expr = a;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 1);
+            }
+
+            {
+                auto transformed_expr = transform(expr, user::empty_xform{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 1);
+            }
+
+            {
+                auto transformed_expr = transform(expr, user::eval_xform_tag{});
+                BOOST_CHECK(transformed_expr.value == 1);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::eval_xform_expr{});
+                BOOST_CHECK(transformed_expr.value == 1);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::eval_xform_both{});
+                BOOST_CHECK(transformed_expr.value == 1);
+            }
+        }
+
+        {
+            auto expr = x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::plus_to_minus_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::plus_to_minus_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::plus_to_minus_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39);
+            }
+        }
+
+        {
+            auto expr = x + user::number{3.0};
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+        }
+
+        {
+            auto expr = x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+        }
+
+        {
+            auto expr = (x + y) + user::number{1.0};
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 46);
+            }
+
+            {
+                // Differs from those below, because it matches terminals, not
+                // expressions.
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 40 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 38 * 2);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::term_nonterm_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 38 * 2);
+            }
+        }
+
+        {
+            auto expr = x + user::number{3.0};
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_tag{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_expr{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_both{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+        }
+
+        {
+            auto expr = x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_tag{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_expr{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_both{});
+                BOOST_CHECK(result.value == 39 * 2);
+            }
+        }
+
+        {
+            auto expr = (x + y) + user::number{1.0};
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 46);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_tag{});
+                BOOST_CHECK(result.value == 38 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_expr{});
+                BOOST_CHECK(result.value == 38 * 2);
+            }
+
+            {
+                user::number result =
+                    transform(expr, user::eval_term_nonterm_xform_both{});
+                BOOST_CHECK(result.value == 38 * 2);
+            }
+        }
+
+        {
+            auto expr = a * x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            auto transformed_expr =
+                transform(expr, user::naxpy_eager_nontemplate_xform);
+            {
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 55);
+            }
+        }
+
+        {
+            auto expr = a + (a * x + y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 46);
+            }
+
+            auto transformed_expr =
+                transform(expr, user::naxpy_eager_nontemplate_xform);
+            {
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 56);
+            }
+        }
+
+        {
+            auto expr = a * x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            auto transformed_expr =
+                transform(expr, user::naxpy_lazy_nontemplate_xform);
+            {
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 55);
+            }
+        }
+
+        {
+            auto expr = a + (a * x + y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 46);
+            }
+
+            auto transformed_expr =
+                transform(expr, user::naxpy_lazy_nontemplate_xform);
+            {
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 56);
+            }
+        }
+
+        {
+            auto expr = (a * x + y) * (a * x + y) + (a * x + y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 45 * 45 + 45);
+            }
+
+            auto transformed_expr = transform(expr, user::naxpy_xform{});
+            {
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 55 * 55 + 55 + 10);
+            }
+        }
+    }
+
+    {
+        term<double> unity{1.0};
+        term<std::unique_ptr<int>> i{new int{7}};
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<std::unique_ptr<int>>>>
+            expr_1 = unity + std::move(i);
+
+        yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<
+                ref<term<double> &>,
+                yap::expression<
+                    yap::expr_kind::plus,
+                    bh::tuple<
+                        ref<term<double> &>,
+                        term<std::unique_ptr<int>>>>>>
+            expr_2 = unity + std::move(expr_1);
+
+        auto transformed_expr = transform(std::move(expr_2), double_to_float);
+
+        transform(std::move(transformed_expr), check_unique_ptrs_equal_7);
+    }
+
+    {
+        term<user::number> a{{1.0}};
+        term<user::number> x{{42.0}};
+        term<user::number> y{{3.0}};
+
+        {
+            auto expr = -x;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == -42);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 42);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 42);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 42);
+            }
+        }
+
+        {
+            auto expr = a * -x + y;
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == -39);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+        }
+
+        {
+            auto expr = -(x + y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == -45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::disable_negate_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 45);
+            }
+        }
+    }
+
+    {
+        term<user::number> a{{1.0}};
+        term<user::number> x{{42.0}};
+        term<user::number> y{{3.0}};
+
+        {
+            auto expr = if_else(0 < a, x, y);
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 42);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 3);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 3);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 3);
+            }
+        }
+
+        {
+            auto expr = y * if_else(0 < a, x, y) + user::number{0.0};
+            {
+                user::number result = evaluate(expr);
+                BOOST_CHECK(result.value == 126);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_tag{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 9);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_expr{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 9);
+            }
+
+            {
+                auto transformed_expr =
+                    transform(expr, user::ternary_to_else_xform_both{});
+                user::number result = evaluate(transformed_expr);
+                BOOST_CHECK(result.value == 9);
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/user_expression_transform_2.cpp b/src/boost/libs/yap/test/user_expression_transform_2.cpp
new file mode 100644
index 00000000..da231b4b
--- /dev/null
+++ b/src/boost/libs/yap/test/user_expression_transform_2.cpp
@@ -0,0 +1,257 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+namespace user {
+
+    struct number
+    {
+        double value;
+    };
+
+    struct eval_xform
+    {
+        auto
+        operator()(yap::expr_tag<yap::expr_kind::terminal>, number const & n)
+        {
+            return n;
+        }
+
+        template<typename Expr>
+        decltype(auto) operator()(
+            yap::expression<yap::expr_kind::negate, bh::tuple<Expr>> const &
+                expr)
+        {
+            number const n = transform(yap::value(expr), *this);
+            return number{-n.value};
+        }
+
+        template<typename Expr1, typename Expr2>
+        decltype(auto) operator()(yap::expression<
+                                  yap::expr_kind::plus,
+                                  bh::tuple<Expr1, Expr2>> const & expr)
+        {
+            number const lhs = transform(yap::left(expr), *this);
+            number const rhs = transform(yap::right(expr), *this);
+            return number{lhs.value + rhs.value};
+        }
+    };
+}
+
+template<typename Expr>
+auto make_ref(Expr && expr)
+{
+    using type = yap::detail::operand_type_t<yap::expression, Expr>;
+    return yap::detail::make_operand<type>{}(static_cast<Expr &&>(expr));
+}
+
+int test_main(int, char * [])
+{
+{
+    {
+        term<user::number> a{{1.0}};
+
+        {
+            user::number result = transform(a, user::eval_xform{});
+            BOOST_CHECK(result.value == 1);
+        }
+
+        {
+            user::number result = transform(make_ref(a), user::eval_xform{});
+            BOOST_CHECK(result.value == 1);
+        }
+
+        {
+            user::number result = transform(-a, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr = make_ref(a);
+            user::number result = transform(-expr, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr = -a;
+            user::number result = transform(expr, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr1 = make_ref(a);
+            auto expr2 = make_ref(expr1);
+            user::number result = transform(expr2, user::eval_xform{});
+            BOOST_CHECK(result.value == 1);
+        }
+
+        {
+            auto expr1 = -a;
+            auto expr2 = make_ref(expr1);
+            user::number result = transform(expr2, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr1 = make_ref(a);
+            auto expr2 = -expr1;
+            user::number result = transform(expr2, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr1 = a;
+            auto expr2 = make_ref(expr1);
+            auto expr3 = make_ref(expr2);
+            user::number result = transform(expr3, user::eval_xform{});
+            BOOST_CHECK(result.value == 1);
+        }
+
+        {
+            auto expr1 = -a;
+            auto expr2 = make_ref(expr1);
+            auto expr3 = make_ref(expr2);
+            user::number result = transform(expr3, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr1 = make_ref(a);
+            auto expr2 = -expr1;
+            auto expr3 = make_ref(expr2);
+            user::number result = transform(expr3, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+
+        {
+            auto expr1 = make_ref(a);
+            auto expr2 = make_ref(expr1);
+            auto expr3 = -expr2;
+            user::number result = transform(expr3, user::eval_xform{});
+            BOOST_CHECK(result.value == -1);
+        }
+    }
+
+    {
+        user::number result =
+            transform(-term<user::number>{{1.0}}, user::eval_xform{});
+        BOOST_CHECK(result.value == -1);
+    }
+}
+
+{
+    term<user::number> a{{1.0}};
+    term<user::number> x{{41.0}};
+
+    {
+        user::number result = transform(a + x, user::eval_xform{});
+        BOOST_CHECK(result.value == 42);
+    }
+
+
+    {
+        user::number result =
+            transform(make_ref(a) + make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == 42);
+    }
+
+    {
+        user::number result = transform(make_ref(a) + x, user::eval_xform{});
+        BOOST_CHECK(result.value == 42);
+    }
+
+    {
+        user::number result = transform(a + make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == 42);
+    }
+
+    {
+        user::number result = transform(a + x, user::eval_xform{});
+        BOOST_CHECK(result.value == 42);
+    }
+
+
+    {
+        user::number result =
+            transform(-make_ref(a) + make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == 40);
+    }
+
+    {
+        user::number result = transform(-make_ref(a) + x, user::eval_xform{});
+        BOOST_CHECK(result.value == 40);
+    }
+
+    {
+        user::number result = transform(-a + make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == 40);
+    }
+
+    {
+        user::number result = transform(-a + x, user::eval_xform{});
+        BOOST_CHECK(result.value == 40);
+    }
+
+
+    {
+        user::number result =
+            transform(make_ref(a) + -make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == -40);
+    }
+
+    {
+        user::number result = transform(make_ref(a) + -x, user::eval_xform{});
+        BOOST_CHECK(result.value == -40);
+    }
+
+    {
+        user::number result = transform(a + -make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == -40);
+    }
+
+    {
+        user::number result = transform(a + -x, user::eval_xform{});
+        BOOST_CHECK(result.value == -40);
+    }
+
+
+    {
+        user::number result =
+            transform(-make_ref(a) + -make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == -42);
+    }
+
+    {
+        user::number result = transform(-make_ref(a) + -x, user::eval_xform{});
+        BOOST_CHECK(result.value == -42);
+    }
+
+    {
+        user::number result = transform(-a + -make_ref(x), user::eval_xform{});
+        BOOST_CHECK(result.value == -42);
+    }
+
+    {
+        user::number result = transform(-a + -x, user::eval_xform{});
+        BOOST_CHECK(result.value == -42);
+    }
+}
+
+return 0;
+}
diff --git a/src/boost/libs/yap/test/value.cpp b/src/boost/libs/yap/test/value.cpp
new file mode 100644
index 00000000..5ca933af
--- /dev/null
+++ b/src/boost/libs/yap/test/value.cpp
@@ -0,0 +1,208 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/expression.hpp>
+
+#include <boost/mpl/assert.hpp>
+
+#include <boost/test/minimal.hpp>
+
+
+template<typename T>
+using term = boost::yap::terminal<boost::yap::expression, T>;
+
+template<typename T>
+using ref = boost::yap::expression_ref<boost::yap::expression, T>;
+
+namespace yap = boost::yap;
+namespace bh = boost::hana;
+
+
+template<boost::yap::expr_kind Kind, typename Tuple>
+struct user_expr
+{
+    static boost::yap::expr_kind const kind = Kind;
+
+    Tuple elements;
+};
+
+BOOST_YAP_USER_BINARY_OPERATOR(plus, user_expr, user_expr)
+
+template<typename T>
+using user_term = boost::yap::terminal<user_expr, T>;
+
+template<typename T>
+using user_ref = boost::yap::expression_ref<user_expr, T>;
+
+
+int test_main(int, char * [])
+{
+    {
+        {
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(1.0)), double &&>));
+            BOOST_CHECK(yap::value(1.0) == 1.0);
+        }
+
+        {
+            double d = 2.0;
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(d)), double &>));
+            BOOST_CHECK(yap::value(d) == 2.0);
+        }
+
+        {
+            double const d = 3.0;
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(d)), double const &>));
+            BOOST_CHECK(yap::value(d) == 3.0);
+        }
+    }
+
+    {
+        {
+            term<double> td = {{1.0}};
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(std::move(td))), double &&>));
+            BOOST_CHECK(yap::value(std::move(td)) == 1.0);
+        }
+
+        {
+            term<double> td = {{2.0}};
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(td)), double &>));
+            BOOST_CHECK(yap::value(td) == 2.0);
+        }
+
+        {
+            term<double> const td = {{3.0}};
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(td)), double const &>));
+            BOOST_CHECK(yap::value(td) == 3.0);
+        }
+
+        term<double> unity = {{1.0}};
+        using plus_expr_type = yap::expression<
+            yap::expr_kind::plus,
+            bh::tuple<ref<term<double> &>, term<int>>>;
+        plus_expr_type plus_expr = unity + term<int>{{1}};
+
+        {
+            ref<term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(std::move(ref))), double &>));
+        }
+
+        {
+            ref<term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(ref)), double &>));
+        }
+
+        {
+            ref<term<double> &> const ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(ref)), double &>));
+        }
+
+        {
+            term<double> const unity = {{1.0}};
+            yap::expression<
+                yap::expr_kind::plus,
+                bh::tuple<ref<term<double> const &>, term<int>>>
+                plus_expr = unity + term<int>{{1}};
+
+            {
+                ref<term<double> const &> ref = bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::value(std::move(ref))),
+                                  double const &>));
+            }
+
+            {
+                ref<term<double> const &> ref = bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<decltype(yap::value(ref)), double const &>));
+            }
+
+            {
+                ref<term<double> const &> const ref = bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<decltype(yap::value(ref)), double const &>));
+            }
+        }
+    }
+
+    {
+        {
+            user_term<double> td = {{1.0}};
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(std::move(td))), double &&>));
+            BOOST_CHECK(yap::value(std::move(td)) == 1.0);
+        }
+
+        {
+            user_term<double> td = {{2.0}};
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(td)), double &>));
+            BOOST_CHECK(yap::value(td) == 2.0);
+        }
+
+        {
+            user_term<double> const td = {{3.0}};
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(td)), double const &>));
+            BOOST_CHECK(yap::value(td) == 3.0);
+        }
+
+        user_term<double> unity = {{1.0}};
+        using plus_expr_type = user_expr<
+            yap::expr_kind::plus,
+            bh::tuple<user_ref<user_term<double> &>, user_term<int>>>;
+        plus_expr_type plus_expr = unity + user_term<int>{{1}};
+
+        {
+            user_ref<user_term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT(
+                (std::is_same<decltype(yap::value(std::move(ref))), double &>));
+        }
+
+        {
+            user_ref<user_term<double> &> ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(ref)), double &>));
+        }
+
+        {
+            user_ref<user_term<double> &> const ref = bh::front(plus_expr.elements);
+            BOOST_MPL_ASSERT((std::is_same<decltype(yap::value(ref)), double &>));
+        }
+
+        {
+            user_term<double> const unity = {{1.0}};
+            user_expr<
+                yap::expr_kind::plus,
+                bh::tuple<user_ref<user_term<double> const &>, user_term<int>>>
+                plus_expr = unity + user_term<int>{{1}};
+
+            {
+                user_ref<user_term<double> const &> ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT((std::is_same<
+                                  decltype(yap::value(std::move(ref))),
+                                  double const &>));
+            }
+
+            {
+                user_ref<user_term<double> const &> ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<decltype(yap::value(ref)), double const &>));
+            }
+
+            {
+                user_ref<user_term<double> const &> const ref =
+                    bh::front(plus_expr.elements);
+                BOOST_MPL_ASSERT(
+                    (std::is_same<decltype(yap::value(ref)), double const &>));
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/src/boost/libs/yap/test/vector_alloc_test.cpp b/src/boost/libs/yap/test/vector_alloc_test.cpp
new file mode 100644
index 00000000..8ab808c2
--- /dev/null
+++ b/src/boost/libs/yap/test/vector_alloc_test.cpp
@@ -0,0 +1,172 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+#include <boost/yap/yap.hpp>
+
+#include <vector>
+#include <iostream>
+
+#include <boost/test/minimal.hpp>
+
+
+int allocations = 0;
+
+void * operator new(std::size_t size)
+{
+    ++allocations;
+    void * retval = malloc(size);
+    if (!retval)
+        throw std::bad_alloc();
+    return retval;
+}
+
+void operator delete(void * ptr) noexcept { free(ptr); }
+
+
+struct take_nth
+{
+    template<typename T>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+        std::vector<T> const & vec)
+    {
+        return boost::yap::make_terminal(vec[n]);
+    }
+
+    std::size_t n;
+};
+
+struct equal_sizes_impl
+{
+    template<typename T>
+    auto operator()(
+        boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
+        std::vector<T> const & vec)
+    {
+        auto const expr_size = vec.size();
+        if (expr_size != size)
+            value = false;
+        return 0;
+    }
+
+    std::size_t const size;
+    bool value;
+};
+
+template<typename Expr>
+bool equal_sizes(std::size_t size, Expr const & expr)
+{
+    equal_sizes_impl impl{size, true};
+    boost::yap::transform(boost::yap::as_expr(expr), impl);
+    return impl.value;
+}
+
+
+template<typename T, typename Expr>
+std::vector<T> & assign(std::vector<T> & vec, Expr const & e)
+{
+    decltype(auto) expr = boost::yap::as_expr(e);
+    assert(equal_sizes(vec.size(), expr));
+    for (std::size_t i = 0, size = vec.size(); i < size; ++i) {
+        vec[i] = boost::yap::evaluate(
+            boost::yap::transform(boost::yap::as_expr(expr), take_nth{i}));
+    }
+    return vec;
+}
+
+template<typename T, typename Expr>
+std::vector<T> & operator+=(std::vector<T> & vec, Expr const & e)
+{
+    decltype(auto) expr = boost::yap::as_expr(e);
+    assert(equal_sizes(vec.size(), expr));
+    for (std::size_t i = 0, size = vec.size(); i < size; ++i) {
+        vec[i] += boost::yap::evaluate(
+            boost::yap::transform(boost::yap::as_expr(expr), take_nth{i}));
+    }
+    return vec;
+}
+
+template<typename T>
+struct is_vector : std::false_type
+{
+};
+
+template<typename T, typename A>
+struct is_vector<std::vector<T, A>> : std::true_type
+{
+};
+
+BOOST_YAP_USER_UDT_UNARY_OPERATOR(
+    negate, boost::yap::expression, is_vector); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    multiplies, boost::yap::expression, is_vector); // *
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    divides, boost::yap::expression, is_vector); // /
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    modulus, boost::yap::expression, is_vector); // %
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    plus, boost::yap::expression, is_vector); // +
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    minus, boost::yap::expression, is_vector); // -
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    less, boost::yap::expression, is_vector); // <
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    greater, boost::yap::expression, is_vector); // >
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    less_equal, boost::yap::expression, is_vector); // <=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    greater_equal, boost::yap::expression, is_vector); // >=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    equal_to, boost::yap::expression, is_vector); // ==
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    not_equal_to, boost::yap::expression, is_vector); // !=
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    logical_or, boost::yap::expression, is_vector); // ||
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    logical_and, boost::yap::expression, is_vector); // &&
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    bitwise_and, boost::yap::expression, is_vector); // &
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    bitwise_or, boost::yap::expression, is_vector); // |
+BOOST_YAP_USER_UDT_ANY_BINARY_OPERATOR(
+    bitwise_xor, boost::yap::expression, is_vector); // ^
+
+int test_main(int, char * [])
+{
+    int i;
+    int const n = 10;
+    std::vector<int> a(n), b(n), c(n), d(n);
+    std::vector<double> e(n);
+
+    // Reset allocation count.  There should be none from this point on.
+    allocations = 0;
+
+    for (i = 0; i < n; ++i) {
+        a[i] = i;
+        b[i] = 2 * i;
+        c[i] = 3 * i;
+        d[i] = i;
+    }
+
+    assign(b, 2);
+    assign(d, a + b * c);
+
+    if_else(d < 30, b, c);
+    a += if_else(d < 30, b, c);
+
+    assign(e, c);
+    e += e - 4 / (c + 1);
+
+    for (i = 0; i < n; ++i) {
+        std::cout << " a(" << i << ") = " << a[i] << " b(" << i
+                  << ") = " << b[i] << " c(" << i << ") = " << c[i] << " d("
+                  << i << ") = " << d[i] << " e(" << i << ") = " << e[i]
+                  << std::endl;
+    }
+
+    BOOST_CHECK(allocations == 0);
+
+    return 0;
+}