/*
 * Copyright Louis Dionne 2014
 * Distributed under the Boost Software License, Version 1.0.
 *         (See accompanying file LICENSE.md or copy at
 *             http://www.boost.org/LICENSE_1_0.txt)
 */

#include <boost/hana/detail/constexpr.hpp>
#include <boost/hana/detail/static_assert.hpp>
#include <boost/hana/integral.hpp>
#include <boost/hana/list.hpp>
#include <boost/hana/logical.hpp>
using namespace boost::hana;


int main() {
    BOOST_HANA_CONSTEXPR_LAMBDA auto numbers = list_c<int, 5, -1, 0, -7, -2, 0, -5, 4>;
    BOOST_HANA_CONSTEXPR_LAMBDA auto negatives = list_c<int, -1, -7, -2, -5>;

    BOOST_HANA_CONSTEXPR_LAMBDA auto keep_negatives = [](auto n, auto acc) {
        return if_(n < int_<0>, cons(n, acc), acc);
    };

    BOOST_HANA_STATIC_ASSERT(
        foldr(keep_negatives, list_c<int>, numbers) == negatives
    );
}