Re: [Scheme-reports] Are generated toplevel definitions secret?

[Peter Bex <Peter.Bex@x>]

On Sun, Apr 24, 2011 at 05:21:30PM +0200, Peter Bex wrote:
> > Heh, cool.  Fortunately it's not central to my argument.  How about an
> > accessor macro:
> > 
> >       (begin
> >         (define-syntax define-getter
> >           (syntax-rules ()
> >             ((_ var init)
> >              (begin
> >                (define val init)
> >                (define-syntax var
> >                  (syntax-rules ()
> >                    ((_) val)))))))
> > 
> >         (define-getter x 10)
> >         (define-getter y 20))
> > 
> > If I put that in a chicken module, import the module, then evaluate (x)
> > and (y), does that evaluate to 10 and 20, respectively?
> 
> Yeah.  Each macro carries its syntactic information with it, like a
> closure.  So "val" in the macro expansion would refer to the x that is
> defined in that module.

I overlooked the fact that val is used, not var.  This will give an
error because the "val" is defined in a different phase than the "var"
macro is declared. 

If I change (define val init) to (define-for-syntax val init), the
generated "var" macro will pick up on it.  Then it will use the same
"val" for both x and y, and hence it will overwrite the binding.
So it's basically the same as putting this in your module:

(define val 10)
(define val 20)

I'm not 100% sure but I suppose this could be considered a bug.

Cheers,
Peter
-- 
http://sjamaan.ath.cx
--
"The process of preparing programs for a digital computer
 is especially attractive, not only because it can be economically
 and scientifically rewarding, but also because it can be an aesthetic
 experience much like composing poetry or music."
							-- Donald Knuth

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