[Boost-users] Spirit - a Reversed Polish Notation calculator

From: Misza (Misza.B_at_[hidden])
Date: 2005-06-27 07:52:46

I've recently switched from YACC to Spirit
and I've been trying to rewrite some examples
from YACC manual, starting with a RPN calculator.
Based on http://www.boost.org/libs/spirit/doc/grammar.html
I made something like this:

/* #includes and usings */

struct rpn_calc : public grammar<rpn_calc>
{
     template <typename ScannerT>
     struct definition
     {
       definition (rpn_calc const& self)
       {
         expr_add = expr >> ch_p(' ') >>
                    expr >> ch_p(' ') >> ch_p('+');
         expr_sub = expr >> ch_p(' ') >>
                    expr >> ch_p(' ') >> ch_p('-');
         expr_mul = expr >> ch_p(' ') >>
                    expr >> ch_p(' ') >> ch_p('*');
         expr_div = expr >> ch_p(' ') >>
                    expr >> ch_p(' ') >> ch_p('/');
         expr_pow = expr >> ch_p(' ') >>
                    expr >> ch_p(' ') >> ch_p('^');
         expr = expr_add | expr_sub |
                expr_mul | expr_div |
                expr_pow | real_p;
       }
       rule<ScannerT> expr, expr_add,
                      expr_sub, expr_mul,
                      expr_div, expr_pow;
       rule<ScannerT> const&
       start () const { return expr; }
     };
};

int main (void)
{
     rpn_calc calc;
     std::string str("1 2 + 3 4 + *");
     if (parse(str.begin(), str.end(), calc, space_p).full)
         cout << "Parsing succeeded.\n";
     else
         cout << "Parsing failed!\n";
     return 0;
}

Now this compiles OK, but when executed it doesn't
output anything, which means that parse(...) quits
without any warnings - what's the problem?
Am I doing something wrong?

Thanks,
        Misza