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Re: [Scheme-reports] 'else' auxiliary syntax
On Fri, Oct 17, 2014 at 01:29:53PM -0400, John Cowan wrote:
> Per Bothner scripsit:
> > Is the following reasonable (for r7rs)?
> > (define-syntax else
> > (syntax-rules ()
> > ((_ . rest)
> > (syntax-error "invalid use of 'else"))))
> That's a good definition, yes. It's also fine for R5RS, since R5RS leaves
> the question of binding open.
Are you sure? It doesn't mention that else is anything else than a
special thing inside cond or case. It also mentions that macro
definitions shadow variable bindings.
If I understand correctly, that means that this program should
not fail, but simply print "1":
(define (else) 1)
Even if there's a peculiar way in which you can read R5RS that allows
"else" to be bound as syntax, I doubt you'll be able to find an
implementation in which the program above will fail. It would be a
shame if r7rs broke compatibility with these programs.
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