Re: values (Re: R5RS)

["C. Ray C." <crayc at 206 dot 31 dot 63 dot 15>]

On Mon, Feb 28, 2000 at 03:52:26PM -0500, Jim Blandy wrote:
> Going cheerfully but completely off-topic: sure.  But I don't consider
> using Scheme's data structures as containers for arguments and return
> values to be practical, because it's so inconvenient.  It's simply
> nicer to write
> 
>     (define (fetch type source) ...)
> 
> than
> 
>     (define (fetch . args)
>       (let ((type (car args))
>             (source (cadr args)))
>         ...))
> 
> I mean, really.  Whereas in ML, it's just
> 
>     fun fetch (type, source) = ...
> 
> The ( , ) syntax is *not* specifically for function arguments.  It's
> the syntax for building tuples.
> [...deleted]
> Then I can say:
> 
>    let val (quotient, remainder) = divide (a, b)
>    in ...
> 
> You get multiple return values in a completely natural, consistent,
> and convenient form.

That sort of thing would be useful, but a new data type isn't
necessary. Perhaps you could add something like a list binding macro,
where you bind elements in a list to variables. Like, if we called it
"list-let", it could look like this:

(define (l)
	'("First" "Second" "Third"))

(list-let (a b c) (l)
	(display a) (newline)
	(display b) (newline)
	(display c) (newline))

and you'd get:

First
Second
Third

If the list you're using is too short, just plug in empty lists (or maybe
#f) for the remaining variables; if the list is too long, the extra list
elements are ignored.