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/*!
@file
Forward declares `boost::hana::monadic_compose`.
@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)
*/
#ifndef BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
#define BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Composition of monadic functions.
//! @ingroup group-Monad
//!
//! Given two monadic functions `f` and `g`, `monadic_compose` returns
//! a new function equivalent to the composition of `f` with `g`, except
//! the result of `g` is `chain`ed into `f` instead of simply passed to
//! it, as with normal composition. `monadic_compose` satisfies
//! @code
//! monadic_compose(f, g)(x) == chain(g(x), f)
//! @endcode
//!
//!
//! @note
//! Unlike `compose`, `monadic_compose` does not generalize nicely to
//! arities higher than one. Hence, only unary functions may be used
//! with `monadic_compose`.
//!
//!
//! Signature
//! ---------
//! Given a `Monad` `M` and two functions @f$ f : B \to M(C) @f$ and
//! @f$ g : A \to M(B) @f$, the signature is
//! @f$
//! \mathtt{monadic\_compose}
//! : (B \to M(C)) \times (A \to M(B)) \to (A \to M(C))
//! @f$.
//!
//! @param f
//! A monadic function with signature @f$ B \to M(C) @f$.
//!
//! @param g
//! A monadic function with signature @f$ A \to M(B) @f$.
//!
//!
//! @note
//! This method is not tag-dispatched, so it can't be customized directly.
//!
//!
//! Example
//! -------
//! @include example/monadic_compose.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto monadic_compose = [](auto&& f, auto&& g) {
return [perfect-capture](auto&& x) -> decltype(auto) {
return hana::chain(forwarded(g)(forwarded(x)), forwarded(f));
};
};
#else
struct monadic_compose_t {
template <typename F, typename G>
constexpr auto operator()(F&& f, G&& g) const;
};
constexpr monadic_compose_t monadic_compose{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
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