1 // Copyright Louis Dionne 2013-2017
2 // Distributed under the Boost Software License, Version 1.0.
3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
4
5 #include <boost/hana/assert.hpp>
6 #include <boost/hana/config.hpp>
7 #include <boost/hana/equal.hpp>
8 #include <boost/hana/fold_right.hpp>
9 #include <boost/hana/if.hpp>
10 #include <boost/hana/less.hpp>
11 #include <boost/hana/prepend.hpp>
12 #include <boost/hana/tuple.hpp>
13 namespace hana = boost::hana;
14 using namespace hana::literals;
15
16
main()17 int main() {
18 constexpr auto numbers = hana::tuple_c<int, 5, -1, 0, -7, -2, 0, -5, 4>;
19 constexpr auto negatives = hana::tuple_c<int, -1, -7, -2, -5>;
20
21 BOOST_HANA_CONSTEXPR_LAMBDA auto keep_negatives = [](auto n, auto acc) {
22 return hana::if_(n < 0_c, hana::prepend(acc, n), acc);
23 };
24
25 BOOST_HANA_CONSTANT_CHECK(hana::fold_right(numbers, hana::tuple_c<int>, keep_negatives) == negatives);
26 }
27