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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/contains.hpp>
- #include <boost/hana/equal.hpp>
- #include <boost/hana/if.hpp>
- #include <boost/hana/monadic_compose.hpp>
- #include <boost/hana/optional.hpp>
- #include <boost/hana/tuple.hpp>
- #include <boost/hana/type.hpp>
- namespace hana = boost::hana;
- int main() {
- BOOST_HANA_CONSTEXPR_LAMBDA auto block = [](auto ...types) {
- return [=](auto x) {
- return hana::if_(hana::contains(hana::make_tuple(types...), hana::typeid_(x)),
- hana::nothing,
- hana::just(x)
- );
- };
- };
- BOOST_HANA_CONSTEXPR_LAMBDA auto f = block(hana::type_c<double>);
- BOOST_HANA_CONSTEXPR_LAMBDA auto g = block(hana::type_c<int>);
- BOOST_HANA_CONSTEXPR_LAMBDA auto h = hana::monadic_compose(g, f);
- BOOST_HANA_CONSTANT_CHECK(h(1) == hana::nothing); // fails inside g; 1 has type int
- BOOST_HANA_CONSTANT_CHECK(h(1.2) == hana::nothing); // fails inside f; 1.2 has type double
- BOOST_HANA_CONSTEXPR_CHECK(h('x') == hana::just('x')); // ok; 'x' has type char
- }
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