Multiple values for R4RS.

[Morris Katz <mkatz%sesame.stanford.edu@relay.cs.net>]

   Date: Tue, 22 Aug 89 17:14:03 PDT
   From: Norman Adams <adams%tekchips.labs.tek.com@relay.cs.net>
       From: mkatz%sesame.stanford.edu
       I can't imagine how one could create an implementation in which the arity
       information is not already present in some form for procedures that 
       are passed

   Sure, it is present in some form.

   Perhaps each procedure is responsible for coping with wrong number of
   arguments passed in.  Somewhere in the procedure's code are
   instructions that perform the check.  The information is there, but
   with a sufficiently clever compiler -- the sort of implementation I
   find most interesting -- finding that information could be
   impractical, if not intractable.  

Difficult maybe; intractable, I doubt.  I think this same argument could be
given for eliminating continuations from Scheme as they create restrictions on
implementation methodologies.  There is almost always a tradeoff between
graeter functionality and implementation simplicity.  I, for one, think that
the functionality gained by adding ACCEPTS? justifies its complexity.  To
convince me otherwise I am afraid you are going to have to be more specific
about why a good compiler gets screwed by accepts.  It seems to me that a good
compiler should only pay a cost for ACCEPTS? when it is used (as Jinx has
stated).  Isn't this the ideal characterization of a feature?  It only costs
the user when they use it.


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Morry Katz
katz@polya.stanford.edu
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