4 files changed, 118 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/lazy/comonad.cpp b/src/boost/libs/hana/example/lazy/comonad.cpp
new file mode 100644
index 000000000..39bbbea6b
--- /dev/null
+++ b/src/boost/libs/hana/example/lazy/comonad.cpp
@@ -0,0 +1,30 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/eval.hpp>
+#include <boost/hana/extend.hpp>
+#include <boost/hana/extract.hpp>
+#include <boost/hana/lazy.hpp>
+
+#include <sstream>
+namespace hana = boost::hana;
+
+
+int main() {
+    std::stringstream s("1 2 3");
+    auto i = hana::make_lazy([&] {
+        int i;
+        s >> i;
+        return i;
+    })();
+
+    auto i_plus_one = hana::extend(i, [](auto lazy_int) {
+        return hana::eval(lazy_int) + 1;
+    });
+
+    BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 2);
+    BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 3);
+    BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 4);
+}
diff --git a/src/boost/libs/hana/example/lazy/functor.cpp b/src/boost/libs/hana/example/lazy/functor.cpp
new file mode 100644
index 000000000..5fa20ab3b
--- /dev/null
+++ b/src/boost/libs/hana/example/lazy/functor.cpp
@@ -0,0 +1,17 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/eval.hpp>
+#include <boost/hana/functional/placeholder.hpp>
+#include <boost/hana/lazy.hpp>
+#include <boost/hana/transform.hpp>
+namespace hana = boost::hana;
+using hana::_;
+
+
+int main() {
+    static_assert(hana::eval(hana::transform(hana::make_lazy(4 / _)(1), _ * 3)) == (4 / 1) * 3, "");
+
+    hana::transform(hana::make_lazy(4 / _)(0), _ * 3); // never evaluated
+}
diff --git a/src/boost/libs/hana/example/lazy/make.cpp b/src/boost/libs/hana/example/lazy/make.cpp
new file mode 100644
index 000000000..d602c96d4
--- /dev/null
+++ b/src/boost/libs/hana/example/lazy/make.cpp
@@ -0,0 +1,24 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/bool.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/eval.hpp>
+#include <boost/hana/if.hpp>
+#include <boost/hana/lazy.hpp>
+namespace hana = boost::hana;
+
+
+int main() {
+    BOOST_HANA_CONSTEXPR_LAMBDA auto f = hana::make<hana::lazy_tag>([](auto x) {
+        return 1 / x;
+    });
+
+    BOOST_HANA_CONSTEXPR_LAMBDA auto g = hana::make_lazy([](auto x) {
+        return x + 1;
+    });
+
+    BOOST_HANA_CONSTEXPR_CHECK(hana::eval(hana::if_(hana::false_c, f(0), g(0))) == 0 + 1);
+}
diff --git a/src/boost/libs/hana/example/lazy/monad.cpp b/src/boost/libs/hana/example/lazy/monad.cpp
new file mode 100644
index 000000000..f425e2810
--- /dev/null
+++ b/src/boost/libs/hana/example/lazy/monad.cpp
@@ -0,0 +1,47 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/chain.hpp>
+#include <boost/hana/eval.hpp>
+#include <boost/hana/lazy.hpp>
+
+#include <functional>
+#include <iostream>
+#include <sstream>
+namespace hana = boost::hana;
+
+
+template <typename T>
+T read_(std::istream& stream) {
+    T x;
+    stream >> x;
+    std::cout << "read " << x << " from the stream\n";
+    return x;
+}
+
+int main() {
+    std::stringstream ss;
+    int in = 123;
+
+    std::cout << "creating the monadic chain...\n";
+    auto out = hana::make_lazy(read_<int>)(std::ref(ss))
+        | [](auto x) {
+            std::cout << "performing x + 1...\n";
+            return hana::make_lazy(x + 1);
+        }
+        | [](auto x) {
+            std::cout << "performing x / 2...\n";
+            return hana::make_lazy(x / 2);
+        };
+
+    std::cout << "putting " << in << " in the stream...\n";
+    ss << in; // nothing is evaluated yet
+
+    std::cout << "evaluating the monadic chain...\n";
+    auto eout = hana::eval(out);
+
+    std::cout << "the result of the monadic chain is " << eout << "\n";
+    BOOST_HANA_RUNTIME_CHECK(eout == (in + 1) / 2);
+}