/*! @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 <boost/hana/config.hpp> #include <boost/hana/core/when.hpp> 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 <typename M, typename = void> struct cycle_impl : cycle_impl<M, when<true>> { }; struct cycle_t { template <typename Xs, typename N> constexpr auto operator()(Xs&& xs, N const& n) const; }; constexpr cycle_t cycle{}; #endif BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_FWD_CYCLE_HPP