[plt-scheme] problem with example macro

Thanks.

I'm familiar with multiple values but didn't pick up
the hint from values-producing-form and missed it
again in the call-with-values. I thought he was just
making his own version of nth as an example. Must read
more carefully.

Michael


--- Jens Axel Søgaard <jensaxel at soegaard.net> wrote:

> michael rice skrev:
> > Noticed this about the first macro given in
> > "Syntax-rules Primer for the Merely Eccentric" in
> the
> > Macro section of schematics:cookbook.
> > 
> > Hope it's not something I'm doing wrong.
> > 
> > Michael
> > 
> > 
> > (define-syntax nth-value
> >   (syntax-rules ()
> >     ((nth-value n values-producing-form)
> >      (call-with-values
> >        (lambda () values-producing-form)
> >        (lambda all-values
> >          (list-ref all-values n))))))
> > 
> > =================================
> > 
> > Welcome to DrScheme, version 360.
> > Language: Swindle.
> >> (nth-value 3 '(a b c d e f))
> > . list-ref: index 3 too large for list: ((a b c d
> e
> > f))
> 
> 
> Your values-producing-form is '(a b c d e f).
> That produces 1 value. This explains, why the
> error say index 3 is too large.
> 
> Try
> 
> (nth-value 3 (values 'a 'b 'c 'd 'e 'f))
> 
> -- 
> Jens Axel Søgaard
> 
> 



 
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