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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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