Add mp_pairwise_fold

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();
+}