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