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)
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
;
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>;
21 BOOST_HANA_CONSTEXPR_LAMBDA
auto keep_negatives
= [](auto n
, auto acc
) {
22 return hana::if_(n
< 0_c
, hana::prepend(acc
, n
), acc
);
25 BOOST_HANA_CONSTANT_CHECK(hana::fold_right(numbers
, hana::tuple_c
<int>, keep_negatives
) == negatives
);