projects / ceph.git / blame
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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 | ||
| 11 | Well, not really a complex parser, but a parser that parses complex numbers. | |
| 12 | This time, we're using __phoenix__ to do the semantic actions. | |
| 13 | ||
| 14 | Here's a simple parser expression for complex numbers: | |
| 15 | ||
| 16 | '(' >> double_ >> -(',' >> double_) >> ')' | |
| 17 | | double_ | |
| 18 | ||
| 19 | What'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 | ||
| 25 | The 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 | ||
| 30 | This 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 | ||
| 38 | Here goes, this time with actions: | |
| 39 | ||
| 40 | [tutorial_complex_number] | |
| 41 | ||
| 42 | The 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 | |
| 45 | placeholders that we are using (i.e. `_1`, `_2`, etc.). Please be aware | |
| 46 | that we are not using the same placeholders supplied by Phoenix. Take | |
| 47 | note that we are pulling in the placeholders from namespace | |
| 48 | `boost::spirit::qi`. These placeholders are specifically tailored for | |
| 49 | Spirit.] | |
| 50 | ||
| 51 | The `double_` parser attaches this action: | |
| 52 | ||
| 53 | ref(n) = _1 | |
| 54 | ||
| 55 | This 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 | |
| 57 | placeholder for the parsed result attribute. | |
| 58 | ||
| 59 | [endsect] |