1/*!
2@file
3Forward declares `boost::hana::ap`.
4
5Copyright Louis Dionne 2013-2022
6Distributed under the Boost Software License, Version 1.0.
7(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
8 */
9
10#ifndef BOOST_HANA_FWD_AP_HPP
11#define BOOST_HANA_FWD_AP_HPP
12
13#include <boost/hana/config.hpp>
14#include <boost/hana/core/when.hpp>
15
16
17namespace boost { namespace hana {
18 //! Lifted application.
19 //! @ingroup group-Applicative
20 //!
21 //! Specifically, `ap` applies a structure containing functions to a
22 //! structure containing values, and returns a new structure containing
23 //! values. The exact way in which the functions are applied to the values
24 //! depends on the `Applicative`.
25 //!
26 //! `ap` can be called with two arguments or more; the functions in the `f`
27 //! structure are curried and then applied to the values in each `x...`
28 //! structure using the binary form of `ap`. Note that this requires the
29 //! number of `x...` must match the arity of the functions in the `f`
30 //! structure. In other words, `ap(f, x1, ..., xN)` is equivalent to
31 //! @code
32 //! ((curry(f) ap x1) ap x2) ... ap xN
33 //! @endcode
34 //! where `x ap y` is just `ap(x, y)` written in infix notation to
35 //! emphasize the left associativity.
36 //!
37 //!
38 //! Signature
39 //! ---------
40 //! Given an Applicative `A`, the signature is
41 //! @f$ \mathtt{ap} : A(T_1 \times \cdots \times T_n \to U)
42 //! \times A(T_1) \times \cdots \times A(T_n)
43 //! \to A(U) @f$.
44 //!
45 //! @param f
46 //! A structure containing function(s).
47 //!
48 //! @param x...
49 //! Structure(s) containing value(s) and on which `f` is applied. The
50 //! number of structures must match the arity of the functions in the
51 //! `f` structure.
52 //!
53 //!
54 //! Example
55 //! -------
56 //! @include example/ap.cpp
57 //!
58 //! @todo
59 //! Consider giving access to all the arguments to the tag-dispatched
60 //! implementation for performance purposes.
61#ifdef BOOST_HANA_DOXYGEN_INVOKED
62 constexpr auto ap = [](auto&& f, auto&& ...x) -> decltype(auto) {
63 return tag-dispatched;
64 };
65#else
66 template <typename A, typename = void>
67 struct ap_impl : ap_impl<A, when<true>> { };
68
69 struct ap_t {
70 template <typename F, typename X>
71 constexpr decltype(auto) operator()(F&& f, X&& x) const;
72
73 template <typename F, typename ...Xs>
74 constexpr decltype(auto) operator()(F&& f, Xs&& ...xs) const;
75 };
76
77 BOOST_HANA_INLINE_VARIABLE constexpr ap_t ap{};
78#endif
79}} // end namespace boost::hana
80
81#endif // !BOOST_HANA_FWD_AP_HPP
82

source code of boost/libs/hana/include/boost/hana/fwd/ap.hpp