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- // Copyright Louis Dionne 2013-2017
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- #include <boost/hana/assert.hpp>
- #include <boost/hana/config.hpp>
- #include <boost/hana/div.hpp>
- #include <boost/hana/equal.hpp>
- #include <boost/hana/eval_if.hpp>
- #include <boost/hana/integral_constant.hpp>
- #include <boost/hana/lazy.hpp>
- #include <boost/hana/monadic_fold_right.hpp>
- #include <boost/hana/optional.hpp>
- #include <boost/hana/tuple.hpp>
- namespace hana = boost::hana;
- int main() {
- BOOST_HANA_CONSTEXPR_LAMBDA auto safe_div = [](auto x, auto y) {
- return hana::eval_if(y == hana::int_c<0>,
- hana::make_lazy(hana::nothing),
- [=](auto _) {
- return hana::just(_(x) / y);
- }
- );
- };
- // with an initial state
- BOOST_HANA_CONSTANT_CHECK(
- hana::monadic_fold_right<hana::optional_tag>(
- hana::tuple_c<int, 1000, 8, 4>, hana::int_c<2>, safe_div
- )
- ==
- hana::just(hana::int_c<1000> / (hana::int_c<8> / (hana::int_c<4> / hana::int_c<2>)))
- );
- BOOST_HANA_CONSTANT_CHECK(
- hana::monadic_fold_right<hana::optional_tag>(
- hana::tuple_c<int, 1000, 8, 4>, hana::int_c<0>, safe_div
- )
- ==
- hana::nothing
- );
- // without an initial state
- BOOST_HANA_CONSTANT_CHECK(
- hana::monadic_fold_right<hana::optional_tag>(
- hana::tuple_c<int, 1000, 8, 4, 2>, safe_div
- )
- ==
- hana::just(hana::int_c<1000> / (hana::int_c<8> / (hana::int_c<4> / hana::int_c<2>)))
- );
- BOOST_HANA_CONSTANT_CHECK(
- hana::monadic_fold_right<hana::optional_tag>(
- hana::tuple_c<int, 1000, 8, 4, 0>, safe_div
- )
- ==
- hana::nothing
- );
- }
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