Add mp_pairwise_fold

include/boost/mp11/algorithm.hpp

@@ -1229,6 +1229,17 @@ template<class V, template<class...> class F, template<class...> class R> struct
 
 template<class V, class Qf, class Qr> using mp_iterate_q = mp_iterate<V, Qf::template fn, Qr::template fn>;
 
+// mp_pairwise_fold<L, F>
+namespace detail
+{
+
+template<class L, class Q> using mp_pairwise_fold_impl = mp_transform_q<Q, mp_pop_back<L>, mp_pop_front<L>>;
+
+} // namespace detail
+
+template<class L, class Q> using mp_pairwise_fold_q = mp_eval_if<mp_empty<L>, mp_clear<L>, detail::mp_pairwise_fold_impl, L, Q>;
+template<class L, template<class...> class F> using mp_pairwise_fold = mp_pairwise_fold_q<L, mp_quote<F>>;
+
 } // namespace mp11
 } // namespace boost
 

test/Jamfile

@@ -122,6 +122,8 @@ run mp_rotate_right.cpp ;
 run mp_power_set.cpp ;
 run mp_partial_sum.cpp ;
 run mp_iterate.cpp ;
+run mp_pairwise_fold.cpp ;
+run mp_pairwise_fold_q.cpp ;
 
 # integral
 run integral.cpp ;

test/mp_pairwise_fold.cpp

@@ -0,0 +1,49 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://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>
+#include <utility>
+
+struct X1 {};
+struct X2 {};
+struct X3 {};
+struct X4 {};
+
+template<class T, class U> using is_same = typename std::is_same<T, U>::type;
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_pairwise_fold;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<>, mp_list>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1>, mp_list>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2>, mp_list>, mp_list<mp_list<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2, X3>, mp_list>, mp_list<mp_list<X1, X2>, mp_list<X2, X3>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2, X3, X4>, mp_list>, mp_list<mp_list<X1, X2>, mp_list<X2, X3>, mp_list<X3, X4>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<>, std::pair>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1>, std::pair>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2>, std::pair>, mp_list<std::pair<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2, X3>, std::pair>, mp_list<std::pair<X1, X2>, std::pair<X2, X3>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<mp_list<X1, X2, X3, X4>, std::pair>, mp_list<std::pair<X1, X2>, std::pair<X2, X3>, std::pair<X3, X4>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<>, std::pair>, std::tuple<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1>, std::pair>, std::tuple<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2>, std::pair>, std::tuple<std::pair<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2, X3>, std::pair>, std::tuple<std::pair<X1, X2>, std::pair<X2, X3>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2, X3, X4>, std::pair>, std::tuple<std::pair<X1, X2>, std::pair<X2, X3>, std::pair<X3, X4>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<>, is_same>, std::tuple<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1>, is_same>, std::tuple<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2>, is_same>, std::tuple<is_same<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2, X2>, is_same>, std::tuple<is_same<X1, X2>, is_same<X2, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_pairwise_fold<std::tuple<X1, X2, X2, X1>, is_same>, std::tuple<is_same<X1, X2>, is_same<X2, X2>, is_same<X2, X1>>>));
+
+    return boost::report_errors();
+}

test/mp_pairwise_fold_q.cpp

@@ -0,0 +1,18 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/mp11.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::mp11;
+
+template<class L> using is_sorted = mp_none_of<mp_pairwise_fold_q<L, mp_bind<mp_less, _2, _1>>, mp_to_bool>;
+
+int main()
+{
+    BOOST_TEST_TRAIT_TRUE((is_sorted<mp_list<mp_int<0>, mp_int<0>, mp_int<1>, mp_int<3>, mp_int<3>, mp_int<7>>>));
+    BOOST_TEST_TRAIT_FALSE((is_sorted<mp_list<mp_int<0>, mp_int<0>, mp_int<1>, mp_int<3>, mp_int<3>, mp_int<2>>>));
+
+    return boost::report_errors();
+}