From 5de3bf8810edbc841e60d4ff5054fdc8e7f8e160 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Fri, 24 Jul 2015 02:11:40 +0300
Subject: [PATCH] Add mp_fold, mp_reverse_fold.

---
 include/boost/mp11/algorithm.hpp | 63 ++++++++++++++++++++++++++++++++
 test/Jamfile.v2                  |  2 +
 test/mp_fold.cpp                 | 57 +++++++++++++++++++++++++++++
 test/mp_reverse_fold.cpp         | 56 ++++++++++++++++++++++++++++
 4 files changed, 178 insertions(+)
 create mode 100644 test/mp_fold.cpp
 create mode 100644 test/mp_reverse_fold.cpp

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index 6745d70..6cdd387 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -714,7 +714,70 @@ template<template<class...> class L, class T1, class T2, class T3, class T4, cla
 template<class L> using mp_reverse = typename detail::mp_reverse_impl<L>::type;
 
 // mp_fold<L, V, F>
+namespace detail
+{
+
+template<class L, class V, template<class...> class F> struct mp_fold_impl;
+
+#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
+
+template<template<class...> class L, class... T, class V, template<class...> class F> struct mp_fold_impl<L<T...>, V, F>
+{
+    static_assert( sizeof...(T) == 0, "T... must be empty" );
+    using type = V;
+};
+
+#else
+
+template<template<class...> class L, class V, template<class...> class F> struct mp_fold_impl<L<>, V, F>
+{
+    using type = V;
+};
+
+#endif
+
+template<template<class...> class L, class T1, class... T, class V, template<class...> class F> struct mp_fold_impl<L<T1, T...>, V, F>
+{
+    using type = typename mp_fold_impl<L<T...>, F<V, T1>, F>::type;
+};
+
+} // namespace detail
+
+template<class L, class V, template<class...> class F> using mp_fold = typename detail::mp_fold_impl<L, V, F>::type;
+
 // mp_reverse_fold<L, V, F>
+namespace detail
+{
+
+template<class L, class V, template<class...> class F> struct mp_reverse_fold_impl;
+
+#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
+
+template<template<class...> class L, class... T, class V, template<class...> class F> struct mp_reverse_fold_impl<L<T...>, V, F>
+{
+    static_assert( sizeof...(T) == 0, "T... must be empty" );
+    using type = V;
+};
+
+#else
+
+template<template<class...> class L, class V, template<class...> class F> struct mp_reverse_fold_impl<L<>, V, F>
+{
+    using type = V;
+};
+
+#endif
+
+template<template<class...> class L, class T1, class... T, class V, template<class...> class F> struct mp_reverse_fold_impl<L<T1, T...>, V, F>
+{
+    using rest = typename mp_reverse_fold_impl<L<T...>, V, F>::type;
+    using type = F<T1, rest>;
+};
+
+} // namespace detail
+
+template<class L, class V, template<class...> class F> using mp_reverse_fold = typename detail::mp_reverse_fold_impl<L, V, F>::type;
+
 // mp_unique<L>
 
 } // namespace boost
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 30e9cc2..4237816 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -50,6 +50,8 @@ run mp_find_index_if.cpp : : : $(REQ) ;
 run mp_find.cpp : : : $(REQ) ;
 run mp_find_if.cpp : : : $(REQ) ;
 run mp_reverse.cpp : : : $(REQ) ;
+run mp_fold.cpp : : : $(REQ) ;
+run mp_reverse_fold.cpp : : : $(REQ) ;
 
 # integral
 run integral.cpp : : : $(REQ) ;
diff --git a/test/mp_fold.cpp b/test/mp_fold.cpp
new file mode 100644
index 0000000..eb5070a
--- /dev/null
+++ b/test/mp_fold.cpp
@@ -0,0 +1,57 @@
+
+//  Copyright 2015 Peter Dimov.
+//
+// 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/mp11/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+
+struct X1 {};
+struct X2 {};
+struct X3 {};
+struct X4 {};
+
+template<class T1, class T2> struct F {};
+
+int main()
+{
+    using boost::mp_list;
+    using boost::mp_fold;
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<mp_list<>, void, F>, void>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<mp_list<X1>, void, F>, F<void, X1>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<mp_list<X1, X2>, void, F>, F<F<void, X1>, X2>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<mp_list<X1, X2, X3>, void, F>, F<F<F<void, X1>, X2>, X3>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<mp_list<X1, X2, X3, X4>, void, F>, F<F<F<F<void, X1>, X2>, X3>, X4>>));
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<>, void, F>, void>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1>, void, F>, F<void, X1>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1, X2>, void, F>, F<F<void, X1>, X2>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1, X2, X3>, void, F>, F<F<F<void, X1>, X2>, X3>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1, X2, X3, X4>, void, F>, F<F<F<F<void, X1>, X2>, X3>, X4>>));
+    }
+
+    using boost::mp_push_back;
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1, X2, X3, X4>, mp_list<>, mp_push_back>, mp_list<X1, X2, X3, X4>>));
+    }
+
+    using boost::mp_push_front;
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_fold<std::tuple<X1, X2, X3, X4>, mp_list<>, mp_push_front>, mp_list<X4, X3, X2, X1>>));
+    }
+
+    return boost::report_errors();
+}
diff --git a/test/mp_reverse_fold.cpp b/test/mp_reverse_fold.cpp
new file mode 100644
index 0000000..d646a11
--- /dev/null
+++ b/test/mp_reverse_fold.cpp
@@ -0,0 +1,56 @@
+
+//  Copyright 2015 Peter Dimov.
+//
+// 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/mp11/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+
+struct X1 {};
+struct X2 {};
+struct X3 {};
+struct X4 {};
+
+template<class T1, class T2> struct F {};
+
+template<class T, class L> using rev_push_back = boost::mp_push_back<L, T>;
+template<class T, class L> using rev_push_front = boost::mp_push_front<L, T>;
+
+int main()
+{
+    using boost::mp_list;
+    using boost::mp_reverse_fold;
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<mp_list<>, void, F>, void>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<mp_list<X1>, void, F>, F<X1, void>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<mp_list<X1, X2>, void, F>, F<X1, F<X2, void>>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<mp_list<X1, X2, X3>, void, F>, F<X1, F<X2, F<X3, void>>>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<mp_list<X1, X2, X3, X4>, void, F>, F<X1, F<X2, F<X3, F<X4, void>>>>>));
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<>, void, F>, void>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1>, void, F>, F<X1, void>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1, X2>, void, F>, F<X1, F<X2, void>>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1, X2, X3>, void, F>, F<X1, F<X2, F<X3, void>>>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1, X2, X3, X4>, void, F>, F<X1, F<X2, F<X3, F<X4, void>>>>>));
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1, X2, X3, X4>, mp_list<>, rev_push_back>, mp_list<X4, X3, X2, X1>>));
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_reverse_fold<std::tuple<X1, X2, X3, X4>, mp_list<>, rev_push_front>, mp_list<X1, X2, X3, X4>>));
+    }
+
+    return boost::report_errors();
+}