| 1 | // Copyright Louis Dionne 2013-2022 |
|---|---|
| 2 | // Distributed under the Boost Software License, Version 1.0. |
| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
| 4 | |
| 5 | #include <boost/hana/assert.hpp> |
| 6 | #include <boost/hana/config.hpp> |
| 7 | #include <boost/hana/contains.hpp> |
| 8 | #include <boost/hana/equal.hpp> |
| 9 | #include <boost/hana/if.hpp> |
| 10 | #include <boost/hana/monadic_compose.hpp> |
| 11 | #include <boost/hana/optional.hpp> |
| 12 | #include <boost/hana/tuple.hpp> |
| 13 | #include <boost/hana/type.hpp> |
| 14 | namespace hana = boost::hana; |
| 15 | |
| 16 | |
| 17 | int main() { |
| 18 | BOOST_HANA_CONSTEXPR_LAMBDA auto block = [](auto ...types) { |
| 19 | return [=](auto x) { |
| 20 | return hana::if_(hana::contains(hana::make_tuple(types...), hana::typeid_(x)), |
| 21 | hana::nothing, |
| 22 | hana::just(x) |
| 23 | ); |
| 24 | }; |
| 25 | }; |
| 26 | |
| 27 | BOOST_HANA_CONSTEXPR_LAMBDA auto f = block(hana::type_c<double>); |
| 28 | BOOST_HANA_CONSTEXPR_LAMBDA auto g = block(hana::type_c<int>); |
| 29 | BOOST_HANA_CONSTEXPR_LAMBDA auto h = hana::monadic_compose(g, f); |
| 30 | BOOST_HANA_CONSTANT_CHECK(h(1) == hana::nothing); // fails inside g; 1 has type int |
| 31 | BOOST_HANA_CONSTANT_CHECK(h(1.2) == hana::nothing); // fails inside f; 1.2 has type double |
| 32 | BOOST_HANA_CONSTEXPR_CHECK(h('x') == hana::just('x')); // ok; 'x' has type char |
| 33 | } |
| 34 |