Re: [boost] Interest in DSL framework

From: Joel de Guzman (joel_at_[hidden])
Date: 2006-08-11 19:02:07

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