[Boost-users] Spriti parser for boolean expression

Subject: [Boost-users] Spriti parser for boolean expression
From: soumeng78 (soumen78_at_[hidden])
Date: 2012-08-09 06:29:30

Hi,

I'm using spirit first time. I'm trying to write a boolean expression (with
only &, | and ! operators) parser. I've defined my grammar like following:

    template <typename Iterator>
    struct boolean_expression_parser : qi::grammar<Iterator, std::string(),
ascii::space_type>
    {
        boolean_expression_parser() :
boolean_expression_parser::base_type(expr)
        {
            using namespace qi;
            using ascii::char_;
            using boost::spirit::ascii::alnum;
            using namespace qi::labels;

            using phoenix::construct;
            using phoenix::val;
        
            operand %= lexeme[+(alnum)];

            simple_expr %= ('(' > expr > ')') | operand;

            unary_expr  %= ('!' > simple_expr ) ;

            and_expr %= ( expr > '*' > expr);

            or_expr  %= (expr > '|' > expr);

            expr %= simple_expr | unary_expr | *and_expr | *or_expr;

            // on_error<fail>
            //         (
            //             unary_expr,
            //             std::cout
            //             << val("Error! Expecting ")
            //             << _4                               // what
failed?
            //             << val(" here: \"")
            //             << construct<std::string>(_3, _2)   // iterators
to error-pos, end
            //             << val("\"")
            //             << std::endl
            //          );
        }
        
        qi::rule<Iterator, std::string(), ascii::space_type> operand;
        qi::rule<Iterator, std::string(), ascii::space_type> simple_expr;
        qi::rule<Iterator, std::string(), ascii::space_type> unary_expr;
        qi::rule<Iterator, std::string(), ascii::space_type> and_expr;
        qi::rule<Iterator, std::string(), ascii::space_type> or_expr;
        qi::rule<Iterator, std::string(), ascii::space_type> expr;
    };

I'm facing few hurdles here:

1. It's not working for any binary expression (like 'A + B'). It's working
fine for unary expressions (like '!(A)' or '(!A)'.

Can someone point me what I'm doing wrong?

2. I want store it in tree form (as I want to build a BDD out of it). Can
someone point me how to do that? 

3. Also, why on_error<> is not working even when I enable it?

I'm using boost 1.49 and gcc-4.2.2.

Regards,
~ Soumen

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