text: /*=============================================================================
      Copyright (c) 2001-2011 Joel de Guzman
  
      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)
  =============================================================================*/
  #if !defined(SPIRIT_DIFFERENCE_FEBRUARY_11_2007_1250PM)
  #define SPIRIT_DIFFERENCE_FEBRUARY_11_2007_1250PM
  
  #if defined(_MSC_VER)
  #pragma once
  #endif
  
  #include <boost/spirit/home/qi/domain.hpp>
  #include <boost/spirit/home/qi/meta_compiler.hpp>
  #include <boost/spirit/home/qi/parser.hpp>
  #include <boost/spirit/home/qi/detail/attributes.hpp>
  #include <boost/spirit/home/support/info.hpp>
  #include <boost/spirit/home/support/has_semantic_action.hpp>
  #include <boost/spirit/home/support/handles_container.hpp>
  #include <boost/fusion/include/at.hpp>
  
  namespace boost { namespace spirit
  {
      ///////////////////////////////////////////////////////////////////////////
      // Enablers
      ///////////////////////////////////////////////////////////////////////////
      template <>
      struct use_operator<qi::domain, proto::tag::minus> // enables -
        : mpl::true_ {};
  }}
  
  namespace boost { namespace spirit { namespace qi
  {
      template <typename Left, typename Right>
      struct difference : binary_parser<difference<Left, Right> >
      {
          typedef Left left_type;
          typedef Right right_type;
  
          template <typename Context, typename Iterator>
          struct attribute
          {
              typedef typename
                  traits::attribute_of<left_type, Context, Iterator>::type
              type;
          };
  
          difference(Left const& left_, Right const& right_)
            : left(left_), right(right_) {}
  
          template <typename Iterator, typename Context
            , typename Skipper, typename Attribute>
          bool parse(Iterator& first, Iterator const& last
            , Context& context, Skipper const& skipper
            , Attribute& attr_) const
          {
              // Unlike classic Spirit, with this version of difference, the rule
              // lit("policeman") - "police" will always fail to match.
  
              // Spirit2 does not count the matching chars while parsing and
              // there is no reliable and fast way to check if the LHS matches
              // more than the RHS.
  
              // Try RHS first
              Iterator start = first;
              if (right.parse(first, last, context, skipper, unused))
              {
                  // RHS succeeds, we fail.
                  first = start;
                  return false;
              }
              // RHS fails, now try LHS
              return left.parse(first, last, context, skipper, attr_);
          }
  
          template <typename Context>
          info what(Context& context) const
          {
              return info("difference",
                  std::make_pair(left.what(context), right.what(context)));
          }
  
          Left left;
          Right right;
      };
  
      ///////////////////////////////////////////////////////////////////////////
      // Parser generators: make_xxx function (objects)
      ///////////////////////////////////////////////////////////////////////////
      template <typename Elements, typename Modifiers>
      struct make_composite<proto::tag::minus, Elements, Modifiers>
        : make_binary_composite<Elements, difference>
      {};
  }}}
  
  namespace boost { namespace spirit { namespace traits
  {
      ///////////////////////////////////////////////////////////////////////////
      template <typename Left, typename Right>
      struct has_semantic_action<qi::difference<Left, Right> >
        : binary_has_semantic_action<Left, Right> {};
  
      ///////////////////////////////////////////////////////////////////////////
      template <typename Left, typename Right, typename Attribute
        , typename Context, typename Iterator>
      struct handles_container<qi::difference<Left, Right>, Attribute, Context
        , Iterator>
        : binary_handles_container<Left, Right, Attribute, Context, Iterator> {};
  }}}
  
  #endif
  