Re: [boost] Interest in DSL framework

From: Andreas Pokorny (andreas.pokorny_at_[hidden])
Date: 2006-08-11 17:20:47

On Fri, Aug 11, 2006 at 10:02:18AM +0800, Joel de Guzman <joel_at_[hidden]> wrote:
> Andreas Pokorny wrote:
> > On Mon, Aug 07, 2006 at 07:47:43AM +0800, Joel de Guzman <joel_at_[hidden]> wrote:
> >> To be honest, right now, for Spirit-2, I am inclined to use Eric's
> >> proto. It's been there for quite some time now and is quite mature.
> >> But, like your library, there are no docs yet (as far as I know).
> >> I'm not sure when Eric will have the time to get it outside xpressive
> >> as a standalone ET library, for review. At any rate, it would be
> >> interesting if you can form a collaboration with him. So, instead
> >> of having 2 separate ET entries, we can just have one that has the
> >> the best of both. Is that possible at all? Or is your library too
> >> different from Proto?
> > 
> > The whole thing was derived from proto, I changed some type names. Added
> > a rule system. Then the domain_tag used for rule set dispatching, and
> > finally the fusion-2 map to support attributes.
> > With the attributes a DSL can be defined as a S-attributed grammar.
> 
> Ok...
> 
> [snip explanations]
> 
> > I think thats enough for this email at least. I hope I find more 
> > time to write tomorrow
> 
> 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(...); }
  }; 

This weekend I plan to work on the code, clean things up a bit, 
and try to reintegrate everthing into proto again.

Best Regards, 
Andreas Pokorny