63e88f80
 Hu Chunming
提交三方库
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
/*!
@file
Forward declares `boost::hana::chain`.
Copyright Louis Dionne 2013-2022
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_CHAIN_HPP
#define BOOST_HANA_FWD_CHAIN_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
namespace boost { namespace hana {
//! Feed a monadic value into a monadic computation.
//! @ingroup group-Monad
//!
//! Given a monadic value and a monadic function, `chain` feeds the
//! monadic value into the function, thus performing some Monad-specific
//! effects, and returns the result. An implementation of `chain` must
//! satisfy
//! @code
//! chain(xs, f) == flatten(transform(xs, f))
//! @endcode
//!
//!
//! Signature
//! ---------
//! For a monad `M`, given a monadic value of type `M(A)` and a monadic
//! function @f$ f : A \to M(B) @f$, `chain` has the signature
//! @f$
//! \mathtt{chain} : M(A) \times (A \to M(B)) \to M(B)
//! @f$.
//!
//! @param xs
//! A monadic value to be fed to the function `f`.
//!
//! @param f
//! A function taking a normal value in the `xs` structure, and returning
//! a monadic value. This function is called as `f(x)`, where `x` is an
//! element of the structure `xs`.
//!
//!
//! Example
//! -------
//! @include example/chain.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto chain = [](auto&& xs, auto&& f) -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename M, typename = void>
struct chain_impl : chain_impl<M, when<true>> { };
struct chain_t {
template <typename Xs, typename F>
constexpr decltype(auto) operator()(Xs&& xs, F&& f) const;
};
BOOST_HANA_INLINE_VARIABLE constexpr chain_t chain{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FWD_CHAIN_HPP
|
