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Filename : difference.hpp
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/*=============================================================================
    Copyright (c) 2001-2014 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(BOOST_SPIRIT_X3_DIFFERENCE_FEBRUARY_11_2007_1250PM)
#define BOOST_SPIRIT_X3_DIFFERENCE_FEBRUARY_11_2007_1250PM

#include <boost/spirit/home/x3/support/traits/attribute_of.hpp>
#include <boost/spirit/home/x3/support/traits/has_attribute.hpp>
#include <boost/spirit/home/x3/core/parser.hpp>

namespace boost { namespace spirit { namespace x3
{
    template <typename Left, typename Right>
    struct difference : binary_parser<Left, Right, difference<Left, Right>>
    {
        typedef binary_parser<Left, Right, difference<Left, Right>> base_type;
        static bool const handles_container = Left::handles_container;

        constexpr difference(Left const& left, Right const& right)
          : base_type(left, right) {}

        template <typename Iterator, typename Context
          , typename RContext, typename Attribute>
        bool parse(Iterator& first, Iterator const& last
          , Context const& context, RContext& rcontext, Attribute& attr) const
        {
            // Try Right first
            Iterator start = first;
            if (this->right.parse(first, last, context, rcontext, unused))
            {
                // Right succeeds, we fail.
                first = start;
                return false;
            }
            // Right fails, now try Left
            return this->left.parse(first, last, context, rcontext, attr);
        }

        template <typename Left_, typename Right_>
        constexpr difference<Left_, Right_>
        make(Left_ const& left, Right_ const& right) const
        {
            return { left, right };
        }
    };

    template <typename Left, typename Right>
    constexpr difference<
        typename extension::as_parser<Left>::value_type
      , typename extension::as_parser<Right>::value_type>
    operator-(Left const& left, Right const& right)
    {
        return { as_parser(left), as_parser(right) };
    }
}}}

namespace boost { namespace spirit { namespace x3 { namespace traits
{
    template <typename Left, typename Right, typename Context>
    struct attribute_of<x3::difference<Left, Right>, Context>
        : attribute_of<Left, Context> {};

    template <typename Left, typename Right, typename Context>
    struct has_attribute<x3::difference<Left, Right>, Context>
        : has_attribute<Left, Context> {};
}}}}

#endif