boost/hana/monadic_compose.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::monadic_compose`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_MONADIC_COMPOSE_HPP
0011 #define BOOST_HANA_MONADIC_COMPOSE_HPP
0012
0013 #include <boost/hana/fwd/monadic_compose.hpp>
0014
0015 #include <boost/hana/chain.hpp>
0016 #include <boost/hana/concept/monad.hpp>
0017 #include <boost/hana/config.hpp>
0018 #include <boost/hana/core/dispatch.hpp>
0019 #include <boost/hana/functional/partial.hpp>
0020
0021
0022 namespace boost { namespace hana {
0023     namespace detail {
0024         struct monadic_compose_helper {
0025             template <typename F, typename G, typename X>
0026             constexpr decltype(auto) operator()(F&& f, G&& g, X&& x) const {
0027                 using M = typename hana::tag_of<decltype(g(x))>::type;
0028
0029             #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0030                 static_assert(hana::Monad<M>::value,
0031                 "hana::monadic_compose(f, g) requires 'g' to return a monadic value");
0032             #endif
0033
0034                 return hana::chain(static_cast<G&&>(g)(static_cast<X&&>(x)),
0035                                    static_cast<F&&>(f));
0036             }
0037         };
0038     }
0039
0040     //! @cond
0041     template <typename F, typename G>
0042     constexpr auto monadic_compose_t::operator()(F&& f, G&& g) const {
0043         return hana::partial(detail::monadic_compose_helper{},
0044             static_cast<F&&>(f),
0045             static_cast<G&&>(g)
0046         );
0047     }
0048     //! @endcond
0049 }} // end namespace boost::hana
0050
0051 #endif // !BOOST_HANA_MONADIC_COMPOSE_HPP