1 /*! 2 @file 3 Forward declares `boost::hana::concat`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_FWD_CONCAT_HPP 11 #define BOOST_HANA_FWD_CONCAT_HPP 12 13 #include <boost/hana/config.hpp> 14 #include <boost/hana/core/when.hpp> 15 16 17 BOOST_HANA_NAMESPACE_BEGIN 18 //! Combine two monadic structures together. 19 //! @ingroup group-MonadPlus 20 //! 21 //! Given two monadic structures, `concat` combines them together and 22 //! returns a new monadic structure. The exact definition of `concat` 23 //! will depend on the exact model of MonadPlus at hand, but for 24 //! sequences it corresponds intuitively to simple concatenation. 25 //! 26 //! Also note that combination is not required to be commutative. 27 //! In other words, there is no requirement that 28 //! @code 29 //! concat(xs, ys) == concat(ys, xs) 30 //! @endcode 31 //! and indeed it does not hold in general. 32 //! 33 //! 34 //! Signature 35 //! --------- 36 //! Given a `MonadPlus` `M`, the signature of `concat` is 37 //! @f$ \mathtt{concat} : M(T) \times M(T) \to M(T) @f$. 38 //! 39 //! @param xs, ys 40 //! Two monadic structures to combine together. 41 //! 42 //! 43 //! Example 44 //! ------- 45 //! @include example/concat.cpp 46 #ifdef BOOST_HANA_DOXYGEN_INVOKED __anon793cb9580102(auto&& xs, auto&& ys) 47 constexpr auto concat = [](auto&& xs, auto&& ys) { 48 return tag-dispatched; 49 }; 50 #else 51 template <typename M, typename = void> 52 struct concat_impl : concat_impl<M, when<true>> { }; 53 54 struct concat_t { 55 template <typename Xs, typename Ys> 56 constexpr auto operator()(Xs&& xs, Ys&& ys) const; 57 }; 58 59 constexpr concat_t concat{}; 60 #endif 61 BOOST_HANA_NAMESPACE_END 62 63 #endif // !BOOST_HANA_FWD_CONCAT_HPP 64