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/*!
@file
Defines `boost::hana::unfold_left`.
@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_UNFOLD_LEFT_HPP
#define BOOST_HANA_UNFOLD_LEFT_HPP
#include <boost/hana/fwd/unfold_left.hpp>
#include <boost/hana/append.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/empty.hpp>
#include <boost/hana/first.hpp>
#include <boost/hana/functional/partial.hpp>
#include <boost/hana/optional.hpp>
#include <boost/hana/second.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename S>
struct unfold_left_t {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::unfold_left<S> requires 'S' to be a Sequence");
#endif
template <typename State, typename F>
constexpr auto operator()(State&& state, F&& f) const {
return unfold_left_impl<S>::apply(
static_cast<State&&>(state),
static_cast<F&&>(f)
);
}
};
//! @endcond
template <typename S, bool condition>
struct unfold_left_impl<S, when<condition>> : default_ {
struct unfold_left_helper {
template <typename F, typename P>
constexpr auto operator()(F&& f, P&& p) const {
return hana::append(
unfold_left_impl::apply(
hana::first(static_cast<P&&>(p)),
static_cast<F&&>(f)
),
hana::second(static_cast<P&&>(p))
);
}
};
template <typename Init, typename F>
static constexpr auto apply(Init&& init, F&& f) {
decltype(auto) elt = f(static_cast<Init&&>(init));
return hana::maybe(empty<S>(),
hana::partial(unfold_left_helper{}, static_cast<F&&>(f)),
static_cast<decltype(elt)&&>(elt)
);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_UNFOLD_LEFT_HPP
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