63 lines
1.8 KiB
C++
63 lines
1.8 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::extend`.
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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_EXTEND_HPP
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#define BOOST_HANA_FWD_EXTEND_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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//! Comonadic application of a function to a comonadic value.
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//! @ingroup group-Comonad
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//!
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//! Given a comonadic value and a function accepting a comonadic input,
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//! `extend` returns the result of applying the function to that input
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//! inside the comonadic context.
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//!
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//!
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//! Signature
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//! ---------
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//! Given a Comonad `W` and a function of type \f$ W(T) \to U \f$, the
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//! signature is
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//! \f$
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//! \mathtt{extend} : W(T) \times (W(T) \to U) \to W(U)
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//! \f$
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//!
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//! @param w
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//! A comonadic value to call the function with.
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//!
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//! @param f
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//! A function of signature \f$ W(T) \to U \f$ to be applied to its
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//! comonadic argument inside the comonadic context.
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//!
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//!
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//! Example
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//! -------
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//! @include example/extend.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto extend = [](auto&& w, auto&& f) -> decltype(auto) {
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return tag-dispatched;
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};
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#else
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template <typename W, typename = void>
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struct extend_impl : extend_impl<W, when<true>> { };
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struct extend_t {
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template <typename W_, typename F>
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constexpr decltype(auto) operator()(W_&& w, F&& f) const;
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};
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constexpr extend_t extend{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_EXTEND_HPP
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