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- [/==============================================================================
- Copyright (C) 2001-2011 Joel de Guzman
- Copyright (C) 2001-2011 Hartmut Kaiser
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- ===============================================================================/]
- [section Complex - Our first complex parser]
- Well, not really a complex parser, but a parser that parses complex numbers.
- This time, we're using __phoenix__ to do the semantic actions.
- Here's a simple parser expression for complex numbers:
- '(' >> double_ >> -(',' >> double_) >> ')'
- | double_
- What's new? Well, we have:
- # Alternates: e.g. `a | b`. Try `a` first. If it succeeds, good. If not, try the
- next alternative, `b`.
- # Optionals: e.g. -p. Match the parser p zero or one time.
- The complex parser presented above reads as:
- * One or two real numbers in parentheses, separated by comma (the second number is optional)
- * *OR* a single real number.
- This parser can parse complex numbers of the form:
- (123.45, 987.65)
- (123.45)
- 123.45
- [import ../../example/qi/complex_number.cpp]
- Here goes, this time with actions:
- [tutorial_complex_number]
- The full cpp file for this example can be found here: [@../../example/qi/complex_number.cpp]
- [note Those with experience using __phoenix__ might be confused with the
- placeholders that we are using (i.e. `_1`, `_2`, etc.). Please be aware
- that we are not using the same placeholders supplied by Phoenix. Take
- note that we are pulling in the placeholders from namespace
- `boost::spirit::qi`. These placeholders are specifically tailored for
- Spirit.]
- The `double_` parser attaches this action:
- ref(n) = _1
- This assigns the parsed result (actually, the attribute of `double_`) to n.
- `ref(n)` tells Phoenix that `n` is a mutable reference. `_1` is a Phoenix
- placeholder for the parsed result attribute.
- [endsect]
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