Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!alberta!ubc-cs!grads.cs.ubc.ca!manis
From: manis@grads.cs.ubc.ca (Vincent Manis)
Newsgroups: comp.lang.scheme
Subject: Re: "unspecified" and SET!
Message-ID: <2322@ubc-cs.UUCP>
Date: 23 Jun 89 02:01:05 GMT
References: <3902@kalliope.rice.edu> <19890619192610.2.ALAN@PIGPEN.AI.MIT.EDU> <2281@ubc-cs.UUCP> <81872@ti-csl.csc.ti.com>
Sender: news@cs.ubc.ca
Reply-To: manis@grads.cs.ubc.ca (Vincent Manis)
Organization: The Invisible City of Kitezh
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In article <81872@ti-csl.csc.ti.com> gateley@m2.UUCP (John Gateley) writes:
>Do you mean Matthias Felleisen's calculus for Scheme? It is neither a 
>calculus of unspecified values nor silly. It is a better theoretical
>basis for Scheme than the lambda value calculus: it includes both
>set! style side effects and continuations in its equations.

To clarify, let me say emphatically that I *don't* mean Felleisen's
calculus. As John says, Felleisen's work is not at all silly. I was
instead referring to the proposals for #!unspecified, which, is either
the same as `bottom' in denotational semantics or it is not. In the
former case, #!unspecified should be returned, also, in both a
division by 0 and a non-terminating recursion. In the latter case,
#!unspecified is somewhat pointless (set! could just as easily return
`()), unless one has some reason for distinguishing the two.

While I do not care for William of Ockham's metaphysics, there is much
to say for his Razor. 

____________  Vincent Manis                    | manis@cs.ubc.ca
___ \  _____  The Invisible City of Kitezh     | manis@cs.ubc.cdn
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