1 files changed, 144 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/misc/tree.cpp b/src/boost/libs/hana/example/misc/tree.cpp
new file mode 100644
index 000000000..c74a3e2c0
--- /dev/null
+++ b/src/boost/libs/hana/example/misc/tree.cpp
@@ -0,0 +1,144 @@
+// 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/and.hpp>
+#include <boost/hana/ap.hpp>
+#include <boost/hana/assert.hpp>
+#include <boost/hana/concat.hpp>
+#include <boost/hana/equal.hpp>
+#include <boost/hana/flatten.hpp>
+#include <boost/hana/fold_left.hpp>
+#include <boost/hana/lift.hpp>
+#include <boost/hana/sum.hpp>
+#include <boost/hana/transform.hpp>
+#include <boost/hana/tuple.hpp>
+namespace hana = boost::hana;
+
+
+struct tree_tag;
+
+template <typename X, typename Subforest>
+struct node {
+    X value;
+    Subforest subforest;
+
+    using hana_tag = tree_tag;
+};
+
+constexpr auto make_forest = hana::make_tuple;
+
+template <typename X, typename Subforest>
+constexpr auto make_node(X x, Subforest subforest) {
+    return node<X, Subforest>{x, subforest};
+}
+
+namespace boost { namespace hana {
+    //////////////////////////////////////////////////////////////////////////
+    // Comparable
+    //////////////////////////////////////////////////////////////////////////
+    template <>
+    struct equal_impl<tree_tag, tree_tag> {
+        template <typename Node1, typename Node2>
+        static constexpr auto apply(Node1 node1, Node2 node2) {
+            return hana::and_(
+                hana::equal(node1.value, node2.value),
+                hana::equal(node1.subforest, node2.subforest)
+            );
+        }
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // Functor
+    //////////////////////////////////////////////////////////////////////////
+    template <>
+    struct transform_impl<tree_tag> {
+        template <typename Node, typename F>
+        static constexpr auto apply(Node node, F f) {
+            return make_node(
+                f(node.value),
+                hana::transform(node.subforest, [=](auto subtree) {
+                    return hana::transform(subtree, f);
+                })
+            );
+        }
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // Applicative
+    //////////////////////////////////////////////////////////////////////////
+    template <>
+    struct lift_impl<tree_tag> {
+        template <typename X>
+        static constexpr auto apply(X x)
+        { return make_node(x, make_forest()); }
+    };
+
+    template <>
+    struct ap_impl<tree_tag> {
+        template <typename F, typename X>
+        static constexpr auto apply(F f, X x) {
+            return make_node(
+                f.value(x.value),
+                hana::concat(
+                    hana::transform(x.subforest, [=](auto subtree) {
+                        return hana::transform(subtree, f.value);
+                    }),
+                    hana::transform(f.subforest, [=](auto subtree) {
+                        return hana::ap(subtree, x);
+                    })
+                )
+            );
+        }
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // Monad
+    //////////////////////////////////////////////////////////////////////////
+    template <>
+    struct flatten_impl<tree_tag> {
+        template <typename Node>
+        static constexpr auto apply(Node node) {
+            return make_node(
+                node.value.value,
+                hana::concat(
+                    node.value.subforest,
+                    hana::transform(node.subforest, hana::flatten)
+                )
+            );
+        }
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // Foldable
+    //////////////////////////////////////////////////////////////////////////
+    template <>
+    struct fold_left_impl<tree_tag> {
+        template <typename Node, typename State, typename F>
+        static constexpr auto apply(Node node, State state, F f) {
+            return hana::fold_left(node.subforest, f(state, node.value),
+                        [=](auto state, auto subtree) {
+                            return hana::fold_left(subtree, state, f);
+                        });
+        }
+    };
+}}
+
+int main() {
+    constexpr auto tree = make_node(1, make_forest(
+        make_node(2, make_forest()),
+        make_node(3, make_forest()),
+        make_node(4, make_forest())
+    ));
+
+    BOOST_HANA_CONSTEXPR_CHECK(hana::sum<>(tree) == 10);
+
+    BOOST_HANA_CONSTEXPR_CHECK(hana::equal(
+        hana::transform(tree, [](int i) { return i + 1; }),
+        make_node(2, make_forest(
+            make_node(3, make_forest()),
+            make_node(4, make_forest()),
+            make_node(5, make_forest())
+        ))
+    ));
+}