Boost C++ Libraries

libs/spirit/classic/example/fundamental/subrule_calc.cpp

/*=============================================================================
    Copyright (c) 2002-2003 Joel de Guzman
    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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
//
//  This calculator example demontrates the use of subrules.
//  This is discussed in the "Subrule" chapter in the Spirit User's Guide.
//
//  [ JDG 4/11/2002 ]
//
///////////////////////////////////////////////////////////////////////////////

//#define BOOST_SPIRIT_DEBUG        // define this for debug output

#include <boost/spirit/include/classic_core.hpp>
#include <iostream>
#include <string>

using namespace std;
using namespace BOOST_SPIRIT_CLASSIC_NS;

///////////////////////////////////////////////////////////////////////////////
//
//  Semantic actions
//
///////////////////////////////////////////////////////////////////////////////
namespace 
{
    void    do_int(char const* str, char const* end)
    {
        string  s(str, end);
        cout << "PUSH(" << s << ')' << endl;
    }

    void    do_add(char const*, char const*)    { cout << "ADD\n"; }
    void    do_subt(char const*, char const*)   { cout << "SUBTRACT\n"; }
    void    do_mult(char const*, char const*)   { cout << "MULTIPLY\n"; }
    void    do_div(char const*, char const*)    { cout << "DIVIDE\n"; }
    void    do_neg(char const*, char const*)    { cout << "NEGATE\n"; }
}

///////////////////////////////////////////////////////////////////////////////
//
//  Our calculator grammar (using subrules)
//
///////////////////////////////////////////////////////////////////////////////
struct calculator : public grammar<calculator> 
{
    template <typename ScannerT>
    struct definition {

        definition(calculator const& /*self*/)
        {
            first = (

                expression =
                    term
                    >> *(   ('+' >> term)[&do_add]
                        |   ('-' >> term)[&do_subt]
                        )
                ,

                term =
                    factor
                    >> *(   ('*' >> factor)[&do_mult]
                        |   ('/' >> factor)[&do_div]
                        )
                ,

                factor
                    =   lexeme_d[(+digit_p)[&do_int]]
                    |   '(' >> expression >> ')'
                    |   ('-' >> factor)[&do_neg]
                    |   ('+' >> factor)
            );

            BOOST_SPIRIT_DEBUG_NODE(first);
            BOOST_SPIRIT_DEBUG_NODE(expression);
            BOOST_SPIRIT_DEBUG_NODE(term);
            BOOST_SPIRIT_DEBUG_NODE(factor);
        }

        subrule<0>  expression;
        subrule<1>  term;
        subrule<2>  factor;

        rule<ScannerT> first;
        rule<ScannerT> const&
        start() const { return first; }
    };
};

///////////////////////////////////////////////////////////////////////////////
//
//  Main program
//
///////////////////////////////////////////////////////////////////////////////
int
main()
{
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "\t\tA calculator using subrules...\n\n";
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "Type an expression...or [q or Q] to quit\n\n";

    calculator calc;    //  Our parser

    string str;
    while (getline(cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;

        parse_info<> info = parse(str.c_str(), calc, space_p);

        if (info.full)
        {
            cout << "-------------------------\n";
            cout << "Parsing succeeded\n";
            cout << "-------------------------\n";
        }
        else
        {
            cout << "-------------------------\n";
            cout << "Parsing failed\n";
            cout << "stopped at: \": " << info.stop << "\"\n";
            cout << "-------------------------\n";
        }
    }

    cout << "Bye... :-) \n\n";
    return 0;
}