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Diffstat (limited to 'boost/hana/fwd/concat.hpp')
-rw-r--r-- | boost/hana/fwd/concat.hpp | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/boost/hana/fwd/concat.hpp b/boost/hana/fwd/concat.hpp new file mode 100644 index 0000000000..ed87f71ec1 --- /dev/null +++ b/boost/hana/fwd/concat.hpp @@ -0,0 +1,63 @@ +/*! +@file +Forward declares `boost::hana::concat`. + +@copyright Louis Dionne 2013-2016 +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_CONCAT_HPP +#define BOOST_HANA_FWD_CONCAT_HPP + +#include <boost/hana/config.hpp> +#include <boost/hana/core/when.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! Combine two monadic structures together. + //! @ingroup group-MonadPlus + //! + //! Given two monadic structures, `concat` combines them together and + //! returns a new monadic structure. The exact definition of `concat` + //! will depend on the exact model of MonadPlus at hand, but for + //! sequences it corresponds intuitively to simple concatenation. + //! + //! Also note that combination is not required to be commutative. + //! In other words, there is no requirement that + //! @code + //! concat(xs, ys) == concat(ys, xs) + //! @endcode + //! and indeed it does not hold in general. + //! + //! + //! Signature + //! --------- + //! Given a `MonadPlus` `M`, the signature of `concat` is + //! @f$ \mathtt{concat} : M(T) \times M(T) \to M(T) @f$. + //! + //! @param xs, ys + //! Two monadic structures to combine together. + //! + //! + //! Example + //! ------- + //! @include example/concat.cpp +#ifdef BOOST_HANA_DOXYGEN_INVOKED + constexpr auto concat = [](auto&& xs, auto&& ys) { + return tag-dispatched; + }; +#else + template <typename M, typename = void> + struct concat_impl : concat_impl<M, when<true>> { }; + + struct concat_t { + template <typename Xs, typename Ys> + constexpr auto operator()(Xs&& xs, Ys&& ys) const; + }; + + constexpr concat_t concat{}; +#endif +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FWD_CONCAT_HPP |