Re: why undefined return values?

[Eric Marsden <emarsden at mail dot dotcom dot fr>]

>>>>> "ka" == Ken Anderson <kanderso@bbn.com> writes:

  ka> (let ((eof (eof)))
  ka>   (and (not eof) 
  ka>        (let ((match (find-match regexp)))
  ka> 	 (and match
  ka> 	      (let ((str (car match)))
  ka> 		...)))))

     (cond ((eof) #f)
           ((find-match regexp) => car)
           (else #f))


In general, a test based on an expensive or side-effecting
computation, which might be written in CL as 

    (when (setq val (expensive-computation))
      ...)

can be written in R5RS Scheme as

    (cond ((expensive-computation) =>
           (lambda (val) ...)))
            
-- 
Eric Marsden