Re: [Scheme-reports] ANN: first draft of R7RS small language available

[Andre van Tonder <andre@x>]

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

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