1[/==============================================================================
2    Copyright (C) 2001-2011 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
11Well, not really a complex parser, but a parser that parses complex numbers.
12This time, we're using __phoenix__ to do the semantic actions.
13
14Here's a simple parser expression for complex numbers:
15
16        '(' >> double_ >> -(',' >> double_) >> ')'
17    |   double_
18
19What's new? Well, we have:
20
21# Alternates: e.g. `a | b`. Try `a` first. If it succeeds, good. If not, try the
22  next alternative, `b`.
23# Optionals: e.g. -p. Match the parser p zero or one time.
24
25The complex parser presented above reads as:
26
27* One or two real numbers in parentheses, separated by comma (the second number is optional)
28* *OR* a single real number.
29
30This parser can parse complex numbers of the form:
31
32    (123.45, 987.65)
33    (123.45)
34    123.45
35
36[import ../../example/qi/complex_number.cpp]
37
38Here goes, this time with actions:
39
40[tutorial_complex_number]
41
42The full cpp file for this example can be found here: [@../../example/qi/complex_number.cpp]
43
44[note Those with experience using __phoenix__ might be confused with the
45placeholders that we are using (i.e. `_1`, `_2`, etc.). Please be aware
46that we are not using the same placeholders supplied by Phoenix. Take
47note that we are pulling in the placeholders from namespace
48`boost::spirit::qi`. These placeholders are specifically tailored for
49Spirit.]
50
51The `double_` parser attaches this action:
52
53    ref(n) = _1
54
55This assigns the parsed result (actually, the attribute of `double_`) to n.
56`ref(n)` tells Phoenix that `n` is a mutable reference. `_1` is a Phoenix
57placeholder for the parsed result attribute.
58
59[endsect]
60