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1 | [/============================================================================== | |
2 | Copyright (C) 2001-2015 Joel de Guzman | |
3 | Copyright (C) 2001-2011 Hartmut Kaiser | |
4 | ||
5 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
6 | file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
7 | ===============================================================================/] | |
8 | ||
9 | [section Complex - Our first complex parser] | |
10 | ||
11 | Well, not really a complex parser, but a parser that parses complex numbers. | |
12 | ||
13 | Here's a simple parser expression for complex numbers: | |
14 | ||
15 | '(' >> double_ >> -(',' >> double_) >> ')' | |
16 | | double_ | |
17 | ||
18 | What's new? Well, we have: | |
19 | ||
20 | # Alternates: e.g. `a | b`. Try `a` first. If it succeeds, good. If not, try the | |
21 | next alternative, `b`. | |
22 | # Optionals: e.g. -p. Match the parser p zero or one time. | |
23 | ||
24 | The complex parser presented above reads as: | |
25 | ||
26 | * One or two real numbers in parentheses, separated by comma (the second number is optional) | |
27 | * *OR* a single real number. | |
28 | ||
29 | This parser can parse complex numbers of the form: | |
30 | ||
31 | (123.45, 987.65) | |
32 | (123.45) | |
33 | 123.45 | |
34 | ||
35 | Here goes, this time with actions: | |
36 | ||
37 | namespace client | |
38 | { | |
39 | template <typename Iterator> | |
40 | bool parse_complex(Iterator first, Iterator last, std::complex<double>& c) | |
41 | { | |
42 | using boost::spirit::x3::double_; | |
43 | using boost::spirit::x3::_attr; | |
44 | using boost::spirit::x3::phrase_parse; | |
45 | using boost::spirit::x3::ascii::space; | |
46 | ||
47 | double rN = 0.0; | |
48 | double iN = 0.0; | |
49 | auto fr = [&](auto& ctx){ rN = _attr(ctx); }; | |
50 | auto fi = [&](auto& ctx){ iN = _attr(ctx); }; | |
51 | ||
52 | bool r = phrase_parse(first, last, | |
53 | ||
54 | // Begin grammar | |
55 | ( | |
56 | '(' >> double_[fr] | |
57 | >> -(',' >> double_[fi]) >> ')' | |
58 | | double_[fr] | |
59 | ), | |
60 | // End grammar | |
61 | ||
62 | space); | |
63 | ||
64 | if (!r || first != last) // fail if we did not get a full match | |
65 | return false; | |
66 | c = std::complex<double>(rN, iN); | |
67 | return r; | |
68 | } | |
69 | } | |
70 | ||
71 | The full cpp file for this example can be found here: [@../../../example/x3/complex_number.cpp] | |
72 | ||
73 | The `double_` parser attaches this action: | |
74 | ||
75 | [&](auto& ctx){ n = _attr(ctx); } | |
76 | ||
77 | This assigns the parsed result (actually, the attribute of `double_`) to n. | |
78 | ||
79 | [endsect] |