On Tue, 3 May 2011, Andrzej wrote:

> In my implementation I've implemented 'cond' so that it recognizes
> 'else' by looking at the name of the symbol. If I have to fix it I'd
> like to know what the correct version is, why it is correct and why my
> implementation is wrong.

Here is a good example illustrating the problems of your proposed
implementation.

Consider the following inline macro that converts a Scheme value to its boolean
representative:

(define-syntax convert-to-boolean
   (syntax-rules ()
     ((_ exp)
      (cond (exp #t)
            (else #f)))))

Now imagine a user who knows that there are no reserved words in Scheme
and who knows nothing of the implementation of convert-to-boolean
does the following:

   (let ((else #f))
     (convert-to-boolean else))

What answer should he get?
What answer would he get in your implementation?

Andre

_______________________________________________
Scheme-reports mailing list
Scheme-reports@scheme-reports.org
http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports