I want to write a const-expression parser which calculate the result while parsing. When do it with double and int, I don't know how to do, my code like:

namespace b=boost; namespace bs=boost::spirit; namespace bsq=boost::spirit::qi; namespace bp=boost::phoenix;

bsq::real_parser bnf_double; bsq::int_parser bnf_int8; bsq::int_parser bnf_int10; bsq::int_parser bnf_int16;

template <typename Iterator> struct const_expression: bsq::grammar()> {     typedef b::variant result_type;     const_expression() : const_expression::base_type(rstart)     {         using bsq::_val;         using bsq::_1;         using bsq::_a;         result_type result;         rstart =             bnf_double[_val=_1] >>                 *(                     bsq::lit('+') >> bnf_double[how to write here]

[_val += _1] ?

                )             | rint [_val=_1]             ;

        rint =             bsq::lit('0') >> bsq::char_("xX") >> bnf_int16[_val=_1]             | bsq::lit('0') >> bnf_int8[_val=_1]             | bnf_int10[_val=_1]             ;     }

    bsq::rule rstart;     bsq::rule rint; };

Regards Hartmut --------------- Meet me at BoostCon www.boostcon.com