83 lines
2.7 KiB
C++
83 lines
2.7 KiB
C++
|
/*!
|
||
|
|
@file
|
||
|
|
Forward declares `boost::hana::ap`.
|
||
|
|
|
||
|
|
@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_AP_HPP
|
||
|
|
#define BOOST_HANA_FWD_AP_HPP
|
||
|
|
|
||
|
|
#include <boost/hana/config.hpp>
|
||
|
|
#include <boost/hana/core/when.hpp>
|
||
|
|
|
||
|
|
|
||
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
||
|
|
//! Lifted application.
|
||
|
|
//! @ingroup group-Applicative
|
||
|
|
//!
|
||
|
|
//! Specifically, `ap` applies a structure containing functions to a
|
||
|
|
//! structure containing values, and returns a new structure containing
|
||
|
|
//! values. The exact way in which the functions are applied to the values
|
||
|
|
//! depends on the `Applicative`.
|
||
|
|
//!
|
||
|
|
//! `ap` can be called with two arguments or more; the functions in the `f`
|
||
|
|
//! structure are curried and then applied to the values in each `x...`
|
||
|
|
//! structure using the binary form of `ap`. Note that this requires the
|
||
|
|
//! number of `x...` must match the arity of the functions in the `f`
|
||
|
|
//! structure. In other words, `ap(f, x1, ..., xN)` is equivalent to
|
||
|
|
//! @code
|
||
|
|
//! ((f' <ap> x1) <ap> x2) ... <ap> xN
|
||
|
|
//! @endcode
|
||
|
|
//! where `f'` is `f` but containing curried functions instead and
|
||
|
|
//! `x <ap> y` is just `ap(x, y)` written in infix notation to emphasize
|
||
|
|
//! the left associativity.
|
||
|
|
//!
|
||
|
|
//!
|
||
|
|
//! Signature
|
||
|
|
//! ---------
|
||
|
|
//! Given an Applicative `A`, the signature is
|
||
|
|
//! @f$ \mathtt{ap} : A(T_1 \times \cdots \times T_n \to U)
|
||
|
|
//! \times A(T_1) \times \cdots \times A(T_n)
|
||
|
|
//! \to A(U) @f$.
|
||
|
|
//!
|
||
|
|
//! @param f
|
||
|
|
//! A structure containing function(s).
|
||
|
|
//!
|
||
|
|
//! @param x...
|
||
|
|
//! Structure(s) containing value(s) and on which `f` is applied. The
|
||
|
|
//! number of structures must match the arity of the functions in the
|
||
|
|
//! `f` structure.
|
||
|
|
//!
|
||
|
|
//!
|
||
|
|
//! Example
|
||
|
|
//! -------
|
||
|
|
//! @include example/ap.cpp
|
||
|
|
//!
|
||
|
|
//! @todo
|
||
|
|
//! Consider giving access to all the arguments to the tag-dispatched
|
||
|
|
//! implementation for performance purposes.
|
||
|
|
#ifdef BOOST_HANA_DOXYGEN_INVOKED
|
||
|
|
constexpr auto ap = [](auto&& f, auto&& ...x) -> decltype(auto) {
|
||
|
|
return tag-dispatched;
|
||
|
|
};
|
||
|
|
#else
|
||
|
|
template <typename A, typename = void>
|
||
|
|
struct ap_impl : ap_impl<A, when<true>> { };
|
||
|
|
|
||
|
|
struct ap_t {
|
||
|
|
template <typename F, typename X>
|
||
|
|
constexpr decltype(auto) operator()(F&& f, X&& x) const;
|
||
|
|
|
||
|
|
template <typename F, typename ...Xs>
|
||
|
|
constexpr decltype(auto) operator()(F&& f, Xs&& ...xs) const;
|
||
|
|
};
|
||
|
|
|
||
|
|
constexpr ap_t ap{};
|
||
|
|
#endif
|
||
|
|
BOOST_HANA_NAMESPACE_END
|
||
|
|
|
||
|
|
#endif // !BOOST_HANA_FWD_AP_HPP
|