Re: [Chicken-users] how to use define-macro to...

[Alex Sandro Queiroz e Silva]

Hallo,

minh thu escreveu:
> Hi,
>
> 1/
> I'd like to "repeat" this code for a lot of operators (not just + as
> in the following).
> How can I do that ?
>
> (define old+ +)
> (define (+ a b)
>   (if (or (instance-of? a <behavior>) (instance-of? b <behavior>))
>     (create-behavior (list a b) old+)
>     (old+ a b)))
>
> The problem is how to capture the old + (as old+) to use it in the redefinition.
>   

(define-macro (add-behavior op)
 (let ((old (gensym))
       (new (gensym)))
   `(let ((,old ,op)
          (,new (lambda (a b)
                  (if (or (instance-of? a <behavior>) (instance-of? b 
<behavior>))
                      (create-behavior (list a b) ,old)
                      (,old a b)))))
      (set! ,op ,new))))

> 2/
> I could write the following at any place I want to print debug info.
>
> (cond-expand
>   (debug-behaviors (printf "Debugging...~N"))
>   (else)
>
> Note the particular symbol debug-behaviors.
>
> But it's boring; I would prefer have a "debug" macro instead :
>
> (debug
>   (printf "Debugging...~N"))
>
> But I don't know how I can make it expends to nothing as in the else
> clause of the
> cond-expand. I use this :
>
> (define-macro (debug rest)
>   (cond-expand
>     (debug-behaviors rest)
>     (else '(noop))))
>
> I have to use the noop procedure.
>
> Also, can I write a "higher" macro to generate the "debug" one with a
> particular debug-something symbol ?
>   

(cond-expand
 (debug-behaviors (define debugging-behaviors? #t))
 (else (define debugging-behaviors? #f)))

(define-macro (debug . args)
 (when debugging-behaviors?
   `(apply print ,args)))


    I hope this helps, it's not tested :-)

Cheers,
-alex