On Fri, 2009-09-04 at 20:37 -0500, Eduardo Cavazos wrote:
> Hello,
>
> Let's simulate 'procedure-arity' functionality for a few procedures:
>
> (define (procedure-arity f)
> (cdr (assq f (list (cons vector-ref 2)
> (cons vector-set! 3)
> (cons eq? 2)))))
(It would be better to create that a-list only once).
> Here's a basic curry macro:
>
> (define-syntax curry
> (syntax-rules ()
> ((curry (f x)) f)
> ((curry (f x y ...))
> (lambda (x)
> (curry ((lambda (y ...)
> (f x y ...))
> y ...))) )))
>
> You have to specify the arity of the thing you're currying. For example:
>
> (curry (vector-set! x y z))
>
> will give you a curried 'vector-set!'.
>
> Below is some pseudo-code for a "smart-curry" which uses
> procedure-arity. Is something like it possible?
>
> (define-syntax smart-curry
> (lambda (stx)
> (syntax-case stx ()
> ((smart-curry f)
>
> (with-syntax (((x ...) (generate-temporaries
> (iota
> (procedure-arity f)))))
> (syntax (curry (f x ...))))))))
>
> I guess it comes down to, can a macro "eval" that 'f' so that it's a
> procedure which can then be passed to 'procedure-arity'?
Not really. You could syntax->datum it and use eval on that in a
guessed environment, but you're totally guessing the environment, which
is very not good.
> Or is there another approach to something like this?
You could use free-identifier=?, but the f syntax must be an identifier.
(And all the procedures you're interested in must be bound in the
environment of the definition of procedure-arity, but that's the same as
your run-time version.).
(define (procedure-arity f)
(cdr (assp (lambda (x) (free-identifier=? f x))
(list (cons (syntax vector-ref) 2)
(cons (syntax vector-set!) 3)
(cons (syntax eq?) 2)))))
> If stuff like this *is* possible, then I think it's makes a case for
> 'procedure-arity'.
What if the procedure has multiple arities, e.g. a case-lambda or
(lambda args ---). What would smart-curry do? If you only use it with
single arity procedures, then this isn't a problem.
--
: Derick
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