/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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flow.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_FUNCTION_FLOW_H
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#define BOOST_HOF_GUARD_FUNCTION_FLOW_H
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/// flow
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/// ====
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///
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/// Description
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/// -----------
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///
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/// The `flow` function adaptor provides function composition. It is useful as
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/// an alternative to using the pipe operator `|` when chaining functions. It is
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/// similiar to [`compose`](compose.md) except the evaluation order is
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/// reversed. So, `flow(f, g)(0)` is equivalent to `g(f(0))`.
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///
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///
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/// Synopsis
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/// --------
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///
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/// template<class... Fs>
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/// constexpr flow_adaptor<Fs...> flow(Fs... fs);
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///
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/// Semantics
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/// ---------
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///
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/// assert(flow(f, g)(xs...) == g(f(xs...)));
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///
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/// Requirements
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/// ------------
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///
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/// Fs must be:
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///
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/// * [ConstInvocable](ConstInvocable)
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/// * MoveConstructible
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// using namespace boost::hof;
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///
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/// struct increment
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/// {
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/// template<class T>
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/// T operator()(T x) const
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/// {
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/// return x + 1;
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/// }
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/// };
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///
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/// struct decrement
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/// {
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/// template<class T>
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/// T operator()(T x) const
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/// {
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/// return x - 1;
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/// }
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/// };
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///
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/// int main() {
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/// int r = flow(increment(), decrement(), increment())(3);
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/// assert(r == 4);
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/// }
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///
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/// References
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/// ----------
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///
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/// * [Function composition](https://en.wikipedia.org/wiki/Function_composition)
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///
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#include <boost/hof/detail/callable_base.hpp>
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#include <boost/hof/always.hpp>
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#include <boost/hof/detail/delegate.hpp>
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#include <boost/hof/detail/compressed_pair.hpp>
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#include <boost/hof/detail/join.hpp>
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#include <tuple>
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#include <boost/hof/detail/move.hpp>
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#include <boost/hof/detail/make.hpp>
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#include <boost/hof/detail/result_type.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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namespace boost { namespace hof { namespace detail {
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template<class F1, class F2>
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struct flow_kernel : detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>>, compose_function_result_type<F2, F1>
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{
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typedef detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>> base_type;
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BOOST_HOF_INHERIT_CONSTRUCTOR(flow_kernel, base_type)
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BOOST_HOF_RETURNS_CLASS(flow_kernel);
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template<class... Ts>
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constexpr BOOST_HOF_SFINAE_RESULT(const detail::callable_base<F2>&, result_of<const detail::callable_base<F1>&, id_<Ts>...>)
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operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
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(
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BOOST_HOF_MANGLE_CAST(const detail::callable_base<F2>&)(BOOST_HOF_CONST_THIS->second(xs...))(
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BOOST_HOF_MANGLE_CAST(const detail::callable_base<F1>&)(BOOST_HOF_CONST_THIS->first(xs...))(BOOST_HOF_FORWARD(Ts)(xs)...)
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)
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);
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};
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}
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template<class F, class... Fs>
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struct flow_adaptor : detail::flow_kernel<F, BOOST_HOF_JOIN(flow_adaptor, Fs...)>
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{
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typedef flow_adaptor fit_rewritable_tag;
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typedef BOOST_HOF_JOIN(flow_adaptor, Fs...) tail;
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typedef detail::flow_kernel<F, tail> base_type;
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BOOST_HOF_INHERIT_DEFAULT(flow_adaptor, base_type)
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template<class X, class... Xs,
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BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(detail::callable_base<F>, X),
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BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(tail, Xs...)
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>
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constexpr flow_adaptor(X&& f1, Xs&& ... fs)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base_type, X&&, tail) && BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(tail, Xs&&...))
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: base_type(BOOST_HOF_FORWARD(X)(f1), tail(BOOST_HOF_FORWARD(Xs)(fs)...))
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{}
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template<class X,
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BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(detail::callable_base<F>, X)
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>
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constexpr flow_adaptor(X&& f1)
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BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(base_type, X&&)
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: base_type(BOOST_HOF_FORWARD(X)(f1))
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{}
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};
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template<class F>
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struct flow_adaptor<F> : detail::callable_base<F>
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{
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typedef flow_adaptor fit_rewritable_tag;
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BOOST_HOF_INHERIT_DEFAULT(flow_adaptor, detail::callable_base<F>)
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template<class X, BOOST_HOF_ENABLE_IF_CONVERTIBLE(X, detail::callable_base<F>)>
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constexpr flow_adaptor(X&& f1)
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BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(detail::callable_base<F>, X&&)
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: detail::callable_base<F>(BOOST_HOF_FORWARD(X)(f1))
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{}
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};
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template<class F1, class F2>
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struct flow_adaptor<F1, F2>
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: detail::flow_kernel<detail::callable_base<F1>, detail::callable_base<F2>>
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{
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typedef flow_adaptor fit_rewritable_tag;
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typedef detail::flow_kernel<detail::callable_base<F1>, detail::callable_base<F2>> base_type;
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BOOST_HOF_INHERIT_CONSTRUCTOR(flow_adaptor, base_type)
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};
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BOOST_HOF_DECLARE_STATIC_VAR(flow, detail::make<flow_adaptor>);
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}} // namespace boost::hof
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#endif
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