[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

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 

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

(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?


Scheme-reports mailing list