Fw: [plt-scheme] Struggling with macro...

On 5/23/07, Jos K oot <jos.koot at telefonica.net> wrote:
> Hi,
> Your original question was
>
> ;(machine hello ;       (variables (x 1)
> ;                         (y 2)
> ;                         (z 3)))
> ;
> ;to
> ;(let ([mc (make-mc () () () () ())])
> ;     (add-variable-to-mc x 1)
> ;     (add-variable-to-mc z 3)
> ;     mc)
>
> (BTW, the name 'hello' is not used and I guess that (add-variable-to-mc x 1)
> must be (add-variable-to-mc mc x 1))
>

You're right, name will be used... :) This is just the first part of
the macro. and yes, mc was missing in that call to add-variable-to-mc.

> For this I would write:
>
> (define-syntax machine
> (syntax-rules (variables)
>  ((machine name (variables (id v)) ...)
>   (let ((mc (make-mc () () () () ())))
>    (add-variable-to-mc mc id v) ...
>    mc))))
>

Yes, I understand, still it would not allow multiple (id v). Even if
you somehow do that with this framework it would not help me.

I will have in the end something like:
(machine name
   (variables (var val) ...)
   (event name ... ) ...
   )

I want to be able to create the code associated with (variables ...)
and (event ...) inside an environment where mc is defined so I have
there the initial let.
Then I define another macro inside to parse variables, events (only
variables now, I'm ignoring events) which has mc in scope but things
are definitely getting trickier. Defining everything in one go as you
did is not good because I want to have patterns for variables, events,
etc where order doesn't matter.

I currently have:
(define-syntax (machine stx)
    (syntax-case stx ()
      [(_ mname sexps ...)
       (identifier? #'mname) ; fender
       #'(let ([mc (make-mc () () () () ())])
           (letrec-syntax ((defs (λ (x)
                                   (syntax-case x (variables)
                                     [(variables (name value) (... ...))
                                      (andmap identifier #'name (... ...))
                                      (begin
                                        (add-variable-to-mc #'mc
#'name #'value) (... ...))]))))
               (defs sexps) ...
               mc))]))

which, grrrr, is not working. Again, due to name inside the defs macro
(which seems to be expanding only when machine is called and I
understand why). I'm getting:
syntax: missing ellipses with pattern variable in template in: name

:( Any ideas?



> I probably dont grasp your problem. Can you be more specific?
> Jos Koot
>



-- 
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK