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76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
/*!
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@file
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Forward declares `boost::hana::monadic_compose`.
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@copyright Louis Dionne 2013-2016
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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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*/
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#ifndef BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
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#define BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Composition of monadic functions.
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//! @ingroup group-Monad
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//!
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//! Given two monadic functions `f` and `g`, `monadic_compose` returns
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//! a new function equivalent to the composition of `f` with `g`, except
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//! the result of `g` is `chain`ed into `f` instead of simply passed to
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//! it, as with normal composition. `monadic_compose` satisfies
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//! @code
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//! monadic_compose(f, g)(x) == chain(g(x), f)
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//! @endcode
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//!
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//!
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//! @note
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//! Unlike `compose`, `monadic_compose` does not generalize nicely to
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//! arities higher than one. Hence, only unary functions may be used
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//! with `monadic_compose`.
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//!
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//!
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//! Signature
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//! ---------
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//! Given a `Monad` `M` and two functions @f$ f : B \to M(C) @f$ and
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//! @f$ g : A \to M(B) @f$, the signature is
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//! @f$
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//! \mathtt{monadic\_compose}
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//! : (B \to M(C)) \times (A \to M(B)) \to (A \to M(C))
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//! @f$.
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//!
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//! @param f
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//! A monadic function with signature @f$ B \to M(C) @f$.
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//!
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//! @param g
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//! A monadic function with signature @f$ A \to M(B) @f$.
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//!
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//!
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//! @note
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//! This method is not tag-dispatched, so it can't be customized directly.
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//!
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//!
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//! Example
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//! -------
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//! @include example/monadic_compose.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto monadic_compose = [](auto&& f, auto&& g) {
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return [perfect-capture](auto&& x) -> decltype(auto) {
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return hana::chain(forwarded(g)(forwarded(x)), forwarded(f));
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};
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};
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#else
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struct monadic_compose_t {
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template <typename F, typename G>
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constexpr auto operator()(F&& f, G&& g) const;
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};
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constexpr monadic_compose_t monadic_compose{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_MONADIC_COMPOSE_HPP
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