Add mp_filter

test/Jamfile

@@ -48,6 +48,7 @@ run mp_transform_q.cpp ;
 run mp_transform_sf.cpp ;
 run mp_transform_if.cpp ;
 run mp_transform_if_q.cpp ;
+run mp_filter.cpp ;
 run mp_fill.cpp ;
 run mp_count.cpp ;
 run mp_count_if.cpp ;

test/mp_filter.cpp

@@ -0,0 +1,78 @@
+
+// Copyright 2019 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/mp11/integral.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using boost::mp11::mp_int;
+
+template<class N> using mod_2 = mp_int<N::value % 2>;
+template<class N> using mod_3 = mp_int<N::value % 3>;
+template<class N> using mod_6 = mp_int<N::value % 6>;
+
+using boost::mp11::mp_not;
+using boost::mp11::mp_plus;
+
+template<class T> using P1 = mp_not<mod_6<T>>;
+template<class T1, class... T> using P2 = mp_not<mp_plus<T...>>;
+
+using boost::mp11::mp_bool;
+
+template<std::size_t N> struct second_is
+{
+    template<class T1, class T2> using fn = mp_bool< T2::value == N >;
+};
+
+using boost::mp11::mp_first;
+using boost::mp11::mp_filter_q;
+using boost::mp11::mp_iota;
+using boost::mp11::mp_size;
+
+template<class L, std::size_t N> using at_c = mp_first< mp_filter_q< second_is<N>, L, mp_iota<mp_size<L>> > >;
+
+int main()
+{
+    using boost::mp11::mp_iota_c;
+    using boost::mp11::mp_filter;
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_size_t;
+    using boost::mp11::mp_transform;
+
+    {
+        int const N = 12;
+        using L1 = mp_iota_c<N>;
+
+        using R1 = mp_filter<P1, L1>;
+        BOOST_TEST_TRAIT_TRUE((std::is_same<R1, mp_list<mp_size_t<0>, mp_size_t<6>>>));
+
+        using L2 = mp_transform<mod_2, L1>;
+        using L3 = mp_transform<mod_3, L1>;
+        using L6 = mp_transform<mod_6, L1>;
+
+        using R2 = mp_filter<P2, L1, L6>;
+        BOOST_TEST_TRAIT_TRUE((std::is_same<R2, mp_list<mp_size_t<0>, mp_size_t<6>>>));
+
+        using R3 = mp_filter<P2, L1, L2, L3>;
+        BOOST_TEST_TRAIT_TRUE((std::is_same<R3, mp_list<mp_size_t<0>, mp_size_t<6>>>));
+    }
+
+    {
+        int const N = 64;
+        int const M = 17;
+
+        using L1 = mp_iota_c<N>;
+        using R1 = at_c<L1, M>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<R1, mp_size_t<M>>));
+    }
+
+    return boost::report_errors();
+}