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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76  /*! @file Forward declares boost::hana::cycle. @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_CYCLE_HPP #define BOOST_HANA_FWD_CYCLE_HPP #include #include BOOST_HANA_NAMESPACE_BEGIN //! Combine a monadic structure with itself n times. //! @ingroup group-MonadPlus //! //! Given a monadic structure xs and a non-negative number n, //! cycle returns a new monadic structure which is the result of //! combining xs with itself n times using the concat operation. //! In other words, //! @code //! cycle(xs, n) == concat(xs, concat(xs, ... concat(xs, xs))) //! // ^^^^^ n times total //! @endcode //! //! Also note that since concat is required to be associative, we //! could also have written //! @code //! cycle(xs, n) == concat(concat(... concat(xs, xs), xs), xs) //! // ^^^^^ n times total //! @endcode //! //! If n is zero, then the identity of concat, empty, is returned. //! In the case of sequences, this boils down to returning a sequence //! containing n copies of itself; for other models it might differ. //! //! //! Signature //! --------- //! Given an IntegralConstant C and a MonadPlus M, the signature is //! @f$\mathrm{cycle} : M(T) \times C \to M(T) @f$. //! //! @param xs //! A monadic structure to combine with itself a certain number of times. //! //! @param n //! A non-negative IntegralConstant representing the number of times to //! combine the monadic structure with itself. If n is zero, cycle //! returns empty. //! //! //! Example //! ------- //! @include example/cycle.cpp #ifdef BOOST_HANA_DOXYGEN_INVOKED constexpr auto cycle = [](auto&& xs, auto const& n) { return tag-dispatched; }; #else template struct cycle_impl : cycle_impl> { }; struct cycle_t { template constexpr auto operator()(Xs&& xs, N const& n) const; }; constexpr cycle_t cycle{}; #endif BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_FWD_CYCLE_HPP