Boost_1_39_0/boost/spirit/home/qi/operator/difference.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2007 Joel de Guzman
   3
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 =============================================================================*/
   7 #if !defined(SPIRIT_DIFFERENCE_FEB_11_2007_1250PM)
   8 #define SPIRIT_DIFFERENCE_FEB_11_2007_1250PM
   9
  10 #include <boost/spirit/home/qi/domain.hpp>
  11 #include <boost/spirit/home/support/component.hpp>
  12 #include <boost/spirit/home/support/attribute_of.hpp>
  13 #include <vector>
  14
  15 namespace boost { namespace spirit { namespace qi
  16 {
  17     struct difference
  18     {
  19         template <typename Component, typename Context, typename Iterator>
  20         struct attribute
  21         {
  22             typedef typename
  23                 result_of::left<Component>::type
  24             left_type;
  25
  26             typedef typename
  27                 traits::attribute_of<
  28                     qi::domain, left_type, Context, Iterator>::type
  29             type;
  30         };
  31
  32         template <
  33             typename Component
  34           , typename Iterator, typename Context
  35           , typename Skipper, typename Attribute>
  36         static bool parse(
  37             Component const& component
  38           , Iterator& first, Iterator const& last
  39           , Context& context, Skipper const& skipper
  40           , Attribute& attr)
  41         {
  42             typedef typename
  43                 result_of::left<Component>::type::director
  44             ldirector;
  45
  46             typedef typename
  47                 result_of::right<Component>::type::director
  48             rdirector;
  49
  50             // Unlike classic Spirit, with this version of difference, the rule
  51             // lit("policeman") - "police" will always fail to match.
  52
  53             // Spirit2 does not count the matching chars while parsing and
  54             // there is no reliable and fast way to check if the LHS matches
  55             // more than the RHS.
  56
  57             // Try RHS first
  58             Iterator start = first;
  59             if (rdirector::parse(spirit::right(component), first, last, context,
  60                 skipper, unused))
  61             {
  62                 // RHS succeeds, we fail.
  63                 first = start;
  64                 return false;
  65             }
  66             // RHS fails, now try LHS
  67             return ldirector::parse(spirit::left(component), first, last,
  68                 context, skipper, attr);
  69         }
  70
  71         template <typename Component, typename Context>
  72         static std::string what(Component const& component, Context const& ctx)
  73         {
  74             std::string result = "difference[";
  75
  76             typedef typename
  77                 result_of::left<Component>::type::director
  78             ldirector;
  79
  80             typedef typename
  81                 result_of::right<Component>::type::director
  82             rdirector;
  83
  84             result += ldirector::what(spirit::left(component), ctx);
  85             result += ", ";
  86             result += rdirector::what(spirit::right(component), ctx);
  87             result += "]";
  88             return result;
  89         }
  90     };
  91 }}}
  92
  93 #endif