Andreas Pokorny wrote:
Not sure if I follow. I'm an examples type of guy. It would be enlightening if you can provide a simple example. Say, we want to write a DSEL which has primitives a_, b_ and c_ (objects) of types A B and C and operations >> and |. How shall I develop the ET using your library?
Example usage:
a_ >> b_ | c_
Given that a_ >> b_ invokes the operator of the library, e.g. by deriving at least A from a library type, and given the domain_tag can be evaluated from the participating datastructures. These rules have to be written:
// domain: struct example_domain {};
// rules: template<typename EnableIfT> struct rule<example_domain,right_shift_tag,A,B,EnableIfT> : defined, mpl::true_ { typedef TYPE_WHICH_ENCODES_THE_EXPRESSION result_type; static result_type init(A const& a, B const& b) { return result_type(...); } };
template<typename EnableIfT> struct rule<example_domain,bitor_tag,TYPE_WHICH_ENCODES_THE_EXPRESSION,C,EnableIfT> : defined, mpl::true_ { typedef TYPE_WHICH_ENCODES_THE_WHOLE_TREE result_type; static result_type init(A const& a, B const& b) { return result_type(...); } };
Do we have to write rules for all permutations of A and B and C? What about literals and built-in types? Example: a_ >> b_ >> "hi" | c_ >> 12345
This weekend I plan to work on the code, clean things up a bit, and try to reintegrate everthing into proto again.
Sounds good. Thanks! Cheers, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net