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/*!
@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
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