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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::append`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
6 | Distributed 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_APPEND_HPP | |
11 | #define BOOST_HANA_FWD_APPEND_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | ||
17 | BOOST_HANA_NAMESPACE_BEGIN | |
18 | //! Append an element to a monadic structure. | |
19 | //! @ingroup group-MonadPlus | |
20 | //! | |
21 | //! Given an element `x` and a monadic structure `xs`, `append` returns a | |
22 | //! new monadic structure which is the result of lifting `x` into the | |
23 | //! monadic structure and then combining that (to the right) with `xs`. | |
24 | //! In other words, | |
25 | //! @code | |
26 | //! append(xs, x) == concat(xs, lift<Xs>(x)) | |
27 | //! @endcode | |
28 | //! where `Xs` is the tag of `xs`. For sequences, this has the intuitive | |
29 | //! behavior of simply appending an element to the end of the sequence, | |
30 | //! hence the name. | |
31 | //! | |
32 | //! > #### Rationale for not calling this `push_back` | |
33 | //! > See the rationale for using `prepend` instead of `push_front`. | |
34 | //! | |
35 | //! | |
36 | //! Signature | |
37 | //! --------- | |
38 | //! Given a MonadPlus `M`, the signature is | |
39 | //! @f$ \mathtt{append} : M(T) \times T \to M(T) @f$. | |
40 | //! | |
41 | //! @param xs | |
42 | //! A monadic structure that will be combined to the left of the element. | |
43 | //! | |
44 | //! @param x | |
45 | //! An element to combine to the right of the monadic structure. | |
46 | //! | |
47 | //! | |
48 | //! Example | |
49 | //! ------- | |
50 | //! @include example/append.cpp | |
51 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
52 | constexpr auto append = [](auto&& xs, auto&& x) { | |
53 | return tag-dispatched; | |
54 | }; | |
55 | #else | |
56 | template <typename M, typename = void> | |
57 | struct append_impl : append_impl<M, when<true>> { }; | |
58 | ||
59 | struct append_t { | |
60 | template <typename Xs, typename X> | |
61 | constexpr auto operator()(Xs&& xs, X&& x) const; | |
62 | }; | |
63 | ||
64 | constexpr append_t append{}; | |
65 | #endif | |
66 | BOOST_HANA_NAMESPACE_END | |
67 | ||
68 | #endif // !BOOST_HANA_FWD_APPEND_HPP |