64 lines
1.9 KiB
C++
64 lines
1.9 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::concat`.
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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_CONCAT_HPP
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#define BOOST_HANA_FWD_CONCAT_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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//! Combine two monadic structures together.
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//! @ingroup group-MonadPlus
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//!
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//! Given two monadic structures, `concat` combines them together and
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//! returns a new monadic structure. The exact definition of `concat`
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//! will depend on the exact model of MonadPlus at hand, but for
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//! sequences it corresponds intuitively to simple concatenation.
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//!
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//! Also note that combination is not required to be commutative.
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//! In other words, there is no requirement that
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//! @code
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//! concat(xs, ys) == concat(ys, xs)
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//! @endcode
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//! and indeed it does not hold in general.
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//!
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//!
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//! Signature
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//! ---------
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//! Given a `MonadPlus` `M`, the signature of `concat` is
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//! @f$ \mathtt{concat} : M(T) \times M(T) \to M(T) @f$.
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//!
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//! @param xs, ys
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//! Two monadic structures to combine together.
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//!
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//!
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//! Example
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//! -------
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//! @include example/concat.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto concat = [](auto&& xs, auto&& ys) {
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return tag-dispatched;
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};
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#else
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template <typename M, typename = void>
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struct concat_impl : concat_impl<M, when<true>> { };
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struct concat_t {
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template <typename Xs, typename Ys>
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constexpr auto operator()(Xs&& xs, Ys&& ys) const;
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};
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constexpr concat_t concat{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_CONCAT_HPP
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