ceph/src/boost/libs/spirit/doc/qi/complex.qbk

   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]