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1 | /*============================================================================= |
2 | Copyright (c) 1998-2003 Joel de Guzman | |
3 | Copyright (c) 2001 Daniel Nuffer | |
4 | Copyright (c) 2002 Hartmut Kaiser | |
5 | http://spirit.sourceforge.net/ | |
6 | ||
7 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
8 | file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
9 | =============================================================================*/ | |
10 | #if !defined(BOOST_SPIRIT_OPTIONAL_HPP) | |
11 | #define BOOST_SPIRIT_OPTIONAL_HPP | |
12 | ||
13 | #include <boost/spirit/home/classic/namespace.hpp> | |
14 | #include <boost/spirit/home/classic/core/parser.hpp> | |
15 | #include <boost/spirit/home/classic/core/primitives/primitives.hpp> | |
16 | #include <boost/spirit/home/classic/core/composite/composite.hpp> | |
17 | #include <boost/spirit/home/classic/meta/as_parser.hpp> | |
18 | ||
19 | namespace boost { namespace spirit { | |
20 | ||
21 | BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN | |
22 | ||
23 | /////////////////////////////////////////////////////////////////////////// | |
24 | // | |
25 | // optional class | |
26 | // | |
27 | // Handles expressions of the form: | |
28 | // | |
29 | // !a | |
30 | // | |
31 | // where a is a parser. The expression returns a composite | |
32 | // parser that matches its subject zero (0) or one (1) time. | |
33 | // | |
34 | /////////////////////////////////////////////////////////////////////////// | |
35 | struct optional_parser_gen; | |
36 | ||
37 | template <typename S> | |
38 | struct optional | |
39 | : public unary<S, parser<optional<S> > > | |
40 | { | |
41 | typedef optional<S> self_t; | |
42 | typedef unary_parser_category parser_category_t; | |
43 | typedef optional_parser_gen parser_generator_t; | |
44 | typedef unary<S, parser<self_t> > base_t; | |
45 | ||
46 | optional(S const& a) | |
47 | : base_t(a) {} | |
48 | ||
49 | template <typename ScannerT> | |
50 | typename parser_result<self_t, ScannerT>::type | |
51 | parse(ScannerT const& scan) const | |
52 | { | |
53 | typedef typename parser_result<self_t, ScannerT>::type result_t; | |
54 | typedef typename ScannerT::iterator_t iterator_t; | |
55 | iterator_t save = scan.first; | |
56 | if (result_t r = this->subject().parse(scan)) | |
57 | { | |
58 | return r; | |
59 | } | |
60 | else | |
61 | { | |
62 | scan.first = save; | |
63 | return scan.empty_match(); | |
64 | } | |
65 | } | |
66 | }; | |
67 | ||
68 | struct optional_parser_gen | |
69 | { | |
70 | template <typename S> | |
71 | struct result | |
72 | { | |
73 | typedef optional<S> type; | |
74 | }; | |
75 | ||
76 | template <typename S> | |
77 | static optional<S> | |
78 | generate(parser<S> const& a) | |
79 | { | |
80 | return optional<S>(a.derived()); | |
81 | } | |
82 | }; | |
83 | ||
84 | template <typename S> | |
85 | optional<S> | |
86 | operator!(parser<S> const& a); | |
87 | ||
88 | BOOST_SPIRIT_CLASSIC_NAMESPACE_END | |
89 | ||
90 | }} // namespace BOOST_SPIRIT_CLASSIC_NS | |
91 | ||
92 | #endif | |
93 | ||
94 | #include <boost/spirit/home/classic/core/composite/impl/optional.ipp> |