source: NonGTP/Boost/boost/spirit/core/composite/alternative.hpp @ 857

/*=============================================================================
    Copyright (c) 1998-2003 Joel de Guzman
    Copyright (c) 2001 Daniel Nuffer
    Copyright (c) 2002 Hartmut Kaiser
    http://spirit.sourceforge.net/

    Use, modification and distribution is subject to 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_ALTERNATIVE_HPP)
#define BOOST_SPIRIT_ALTERNATIVE_HPP

#include <boost/spirit/core/parser.hpp>
#include <boost/spirit/core/primitives/primitives.hpp>
#include <boost/spirit/core/composite/composite.hpp>
#include <boost/spirit/meta/as_parser.hpp>

namespace boost { namespace spirit {

    ///////////////////////////////////////////////////////////////////////////
    //
    //  alternative class
    //
    //      Handles expressions of the form:
    //
    //          a | b
    //
    //      where a and b are parsers. The expression returns a composite
    //      parser that matches a or b. One (not both) of the operands may
    //      be a literal char, wchar_t or a primitive string char const*,
    //      wchar_t const*.
    //
    //      The expression is short circuit evaluated. b is never touched
    //      when a is returns a successful match.
    //
    ///////////////////////////////////////////////////////////////////////////
    struct alternative_parser_gen;
    
    template <typename A, typename B>
    struct alternative
    :   public binary<A, B, parser<alternative<A, B> > >
    {
        typedef alternative<A, B>               self_t;
        typedef binary_parser_category          parser_category_t;
        typedef alternative_parser_gen          parser_generator_t;
        typedef binary<A, B, parser<self_t> >   base_t;
    
        alternative(A const& a, B const& b)
        : base_t(a, b) {}
    
        template <typename ScannerT>
        typename parser_result<self_t, ScannerT>::type
        parse(ScannerT const& scan) const
        {
            typedef typename parser_result<self_t, ScannerT>::type result_t;
            typedef typename ScannerT::iterator_t iterator_t;
            { // scope for save
                iterator_t save = scan.first;
                if (result_t hit = this->left().parse(scan))
                    return hit;
                scan.first = save;
            }
            return this->right().parse(scan);
        }
    };
    
    struct alternative_parser_gen
    {
        template <typename A, typename B>
        struct result 
        {
            typedef 
                alternative<
                    typename as_parser<A>::type
                  , typename as_parser<B>::type
                > 
            type;
        };
    
        template <typename A, typename B>
        static alternative<
            typename as_parser<A>::type
          , typename as_parser<B>::type
        >
        generate(A const& a, B const& b)
        {
            return alternative<BOOST_DEDUCED_TYPENAME as_parser<A>::type,
                BOOST_DEDUCED_TYPENAME as_parser<B>::type>
                    (as_parser<A>::convert(a), as_parser<B>::convert(b));
        }
    };
    
    template <typename A, typename B>
    alternative<A, B>
    operator|(parser<A> const& a, parser<B> const& b);
    
    template <typename A>
    alternative<A, chlit<char> >
    operator|(parser<A> const& a, char b);
    
    template <typename B>
    alternative<chlit<char>, B>
    operator|(char a, parser<B> const& b);
    
    template <typename A>
    alternative<A, strlit<char const*> >
    operator|(parser<A> const& a, char const* b);
    
    template <typename B>
    alternative<strlit<char const*>, B>
    operator|(char const* a, parser<B> const& b);
    
    template <typename A>
    alternative<A, chlit<wchar_t> >
    operator|(parser<A> const& a, wchar_t b);
    
    template <typename B>
    alternative<chlit<wchar_t>, B>
    operator|(wchar_t a, parser<B> const& b);
    
    template <typename A>
    alternative<A, strlit<wchar_t const*> >
    operator|(parser<A> const& a, wchar_t const* b);
    
    template <typename B>
    alternative<strlit<wchar_t const*>, B>
    operator|(wchar_t const* a, parser<B> const& b);

}} // namespace boost::spirit

#endif

#include <boost/spirit/core/composite/impl/alternative.ipp>