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RECEIVE vs LET-VALUES Lars Thomas Hansen (02 Jul 1999 17:38 UTC)
RECEIVE vs LET-VALUES John David Stone (02 Jul 1999 18:30 UTC)
Re: RECEIVE vs LET-VALUES Lars Thomas Hansen (02 Jul 1999 18:41 UTC)
Re: RECEIVE vs LET-VALUES John David Stone (02 Jul 1999 18:48 UTC)

Re: RECEIVE vs LET-VALUES Lars Thomas Hansen 02 Jul 1999 18:41 UTC

John David Stone writes:

>Lars Thomas Hansen writes:
>
> > A definition of LET-VALUES that is compatible with the MzScheme syntax
> > and that accomplishes the same as RECEIVE is easily defined, however:
> >
> > 	(define-syntax LET-VALUES
> > 	  (syntax-rules ()
> > 	    ((LET-VALUES (?variables ?expr) ?body1 ?body2 ...)
> > 	     (receive ?variables ?expr ?body1 ?body2 ...))))
>
>        Actually, the functionality doesn't quite match, since RECEIVE can
>also accommodate variable-arity formals.  For instance, you can define a
>very general kind of procedure compostion thus:
>
>            (define (compose outer inner)
>              (lambda arguments
>                (receive intermediates (apply inner arguments)
>                  (apply outer intermediates))))
>
>Both OUTER and INNER can have any arity and return any number of values.

I'm puzzled.  By design, my macro for LET-VALUES does not require the
pattern ?VARIABLES to be a list; it can be a single identifier or an
improper list.  Thus:

	(define (compose outer inner)
	  (lambda arguments
	    (let-values (intermediates (apply inner arguments))
	      (apply outer intermediates))))

expands into your code above.  Is there a subtlety I'm missing?

--lars