tree_calc_grammar.hpp

C++的一个好库。。。现在很流行

/*=============================================================================
    Copyright (c) 2001-2003 Daniel Nuffer
    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)
=============================================================================*/
#ifndef BOOST_SPIRIT_TREE_CALC_GRAMMAR_HPP_
#define BOOST_SPIRIT_TREE_CALC_GRAMMAR_HPP_

using namespace boost::spirit;

///////////////////////////////////////////////////////////////////////////////
//
//  Demonstrates the AST and parse trees. This is discussed in the
//  "Trees" chapter in the Spirit User's Guide.
//
///////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////
//
//  Our calculator grammar
//
////////////////////////////////////////////////////////////////////////////
struct calculator : public grammar<calculator>
{
    static const int integerID = 1;
    static const int factorID = 2;
    static const int termID = 3;
    static const int expressionID = 4;

    template <typename ScannerT>
    struct definition
    {
        definition(calculator const& /*self*/)
        {
            //  Start grammar definition
            integer     =   leaf_node_d[ lexeme_d[
                                (!ch_p('-') >> +digit_p)
                            ] ];

            factor      =   integer
                        |   inner_node_d[ch_p('(') >> expression >> ch_p(')')]
                        |   (root_node_d[ch_p('-')] >> factor);

            term        =   factor >>
                            *(  (root_node_d[ch_p('*')] >> factor)
                              | (root_node_d[ch_p('/')] >> factor)
                            );

            expression  =   term >>
                            *(  (root_node_d[ch_p('+')] >> term)
                              | (root_node_d[ch_p('-')] >> term)
                            );
            //  End grammar definition

            // turn on the debugging info.
            BOOST_SPIRIT_DEBUG_RULE(integer);
            BOOST_SPIRIT_DEBUG_RULE(factor);
            BOOST_SPIRIT_DEBUG_RULE(term);
            BOOST_SPIRIT_DEBUG_RULE(expression);
        }

        rule<ScannerT, parser_context<>, parser_tag<expressionID> >   expression;
        rule<ScannerT, parser_context<>, parser_tag<termID> >         term;
        rule<ScannerT, parser_context<>, parser_tag<factorID> >       factor;
        rule<ScannerT, parser_context<>, parser_tag<integerID> >      integer;

        rule<ScannerT, parser_context<>, parser_tag<expressionID> > const&
        start() const { return expression; }
    };
};

#endif