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133 lines
4.8 KiB
C++
133 lines
4.8 KiB
C++
/*!
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@file
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Defines `boost::hana::monadic_fold_left`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_MONADIC_FOLD_LEFT_HPP
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#define BOOST_HANA_MONADIC_FOLD_LEFT_HPP
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#include <boost/hana/fwd/monadic_fold_left.hpp>
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#include <boost/hana/chain.hpp>
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#include <boost/hana/concept/foldable.hpp>
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#include <boost/hana/concept/monad.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <boost/hana/fold_right.hpp>
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#include <boost/hana/functional/curry.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/lift.hpp>
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#include <type_traits>
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BOOST_HANA_NAMESPACE_BEGIN
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template <typename M>
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struct monadic_fold_left_t {
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Monad<M>::value,
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"hana::monadic_fold_left<M> requires 'M' to be a Monad");
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#endif
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template <typename Xs, typename State, typename F>
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constexpr decltype(auto) operator()(Xs&& xs, State&& state, F&& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using MonadicFoldLeft = BOOST_HANA_DISPATCH_IF(monadic_fold_left_impl<S>,
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hana::Foldable<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Foldable<S>::value,
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"hana::monadic_fold_left<M>(xs, state, f) requires 'xs' to be Foldable");
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#endif
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return MonadicFoldLeft::template apply<M>(static_cast<Xs&&>(xs),
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static_cast<State&&>(state),
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static_cast<F&&>(f));
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}
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template <typename Xs, typename F>
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constexpr decltype(auto) operator()(Xs&& xs, F&& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using MonadicFoldLeft = BOOST_HANA_DISPATCH_IF(monadic_fold_left_impl<S>,
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hana::Foldable<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Foldable<S>::value,
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"hana::monadic_fold_left<M>(xs, f) requires 'xs' to be Foldable");
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#endif
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return MonadicFoldLeft::template apply<M>(static_cast<Xs&&>(xs),
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static_cast<F&&>(f));
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}
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};
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namespace detail {
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struct foldlM_helper {
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template <typename F, typename X, typename K, typename Z>
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constexpr decltype(auto) operator()(F&& f, X&& x, K&& k, Z&& z) const {
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return hana::chain(
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static_cast<F&&>(f)(
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static_cast<Z&&>(z),
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static_cast<X&&>(x)
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),
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static_cast<K&&>(k)
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);
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}
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};
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template <typename End, typename M, typename F>
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struct monadic_foldl1_helper {
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F f;
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template <typename X, typename Y>
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constexpr decltype(auto) operator()(X&& x, Y&& y) const
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{ return f(static_cast<X&&>(x), static_cast<Y&&>(y)); }
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template <typename Y>
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constexpr decltype(auto) operator()(End, Y&& y) const
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{ return hana::lift<M>(static_cast<Y&&>(y)); }
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};
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}
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template <typename T, bool condition>
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struct monadic_fold_left_impl<T, when<condition>> : default_ {
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// with state
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template <typename M, typename Xs, typename S, typename F>
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static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) {
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return hana::fold_right(
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static_cast<Xs&&>(xs),
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hana::lift<M>,
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hana::curry<3>(hana::partial(
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detail::foldlM_helper{}, static_cast<F&&>(f)
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))
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)(static_cast<S&&>(s));
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}
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// without state
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template <typename M, typename Xs, typename F>
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static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
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struct end { };
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using G = detail::monadic_foldl1_helper<end, M, typename detail::decay<F>::type>;
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decltype(auto) result = hana::monadic_fold_left<M>(
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static_cast<Xs&&>(xs),
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end{},
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G{static_cast<F&&>(f)}
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);
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static_assert(!std::is_same<
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std::remove_reference_t<decltype(result)>,
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decltype(hana::lift<M>(end{}))
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>{},
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"hana::monadic_fold_left<M>(xs, f) requires 'xs' to be non-empty");
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return result;
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_MONADIC_FOLD_LEFT_HPP
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