[plt-scheme] define-syntax question

File this under "I'm an idiot" ;-)

Thanks for the help.

Mike

> From: Eli Barzilay <eli at barzilay.org>
> Date: Thu, 26 Jun 2003 23:31:21 -0400
> 
> On Jun 26, Michael Vanier wrote:
> > I see the problem now.  syntax-rules requires the pattern to start with the
> > keyword for the macro (here, "label"), and that won't work in this case.
> > I'm not sure how to achieve the effect I want.  I want to be able to say
> > 
> > ((label fact (lambda (n) (if (= n 0) 1 (* n (fact (- n 1))))))
> >  10)
> > 
> > and get 10 factorial.
> 
> How about:
> 
>   (define-syntax label
>     (syntax-rules ()
>       ((label name func) (letrec ((name func)) name))))
> 
> 
> > BTW it's possible that the common lisp term is "labels"; I'm not
> > sure.  This may also be an archaic old lisp form.
> 
> Well, `labels' is just like `letrec', except that using it doesn't
> require `lambda', something like:
> 
>   (define-syntax labels
>     (syntax-rules ()
>       ((labels ((name args b0 b ...) ...) body0 body ...)
>        (letrec ((name (lambda args b0 b ...)) ...) body0 body ...))))
> 
> and you'd use it like this:
> 
>   (labels ((fact (n) (if (= n 0) 1 (* n (fact (- n 1)))))) (fact 10))
> 
> The other CL issue is that the binding is actually a function binding,
> but that's an issue for a different flamewar.
> 
> -- 
>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                   http://www.barzilay.org/                 Maze is Life!
>