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From: moore%cdr.utah.edu@cs.utah.edu (Tim Moore)
Subject: Re: Virtues of Lisp syntax
Date: 22 Sep 90 14:43:02 MDT
Message-ID: <1990Sep22.144303.2945@hellgate.utah.edu>
Organization: University of Utah CS Dept
References: <10722@life.ai.mit.edu> <20501@well.sf.ca.us> <1990Sep18.180829.8801@hellgate.utah.edu> <20692@well.sf.ca.us>

In article <20692@well.sf.ca.us> jjacobs@well.sf.ca.us (Jeffrey Jacobs) writes:
>
>Larry Masinter wrote:
>>>>[As a side note, many learning LISP programmers frequently do
>>>> encounter self-modifying code and are mystified by it, e.g.,
>>>>   (let ((var '(a b c)))
>>>>       ...
>>>>       (nconc var value))
...
>And Tim Moore wrote:
...
>>>It's not legal Common
>>>Lisp code, because the constant may be in read-only memory.
>
>Correct me if I'm wrong, but it seems to me that this *is* legal and
>that the compiler should specifically *not* allocate quoted lists such
>as that to read-only memory!

For better or worse, this is from CLtL2, pg 115:
X3J13 [the body specifying ANSI Common Lisp] voted in January 1989 to
clarify that it is an error to destructively modify any object that
appears as a constant in executable code, whether within a quote
special form or as a self-evaluating form.

I'm not sure where this was specified in the orginal CLtL; obviously
it wasn't specified too clearly or X3J13 wouldn't have needed to
clarify this point.

>Jeffrey M. Jacobs
>ConsArt Systems Inc, Technology & Management Consulting
>P.O. Box 3016, Manhattan Beach, CA 90266
>voice: (213)376-3802, E-Mail: 76702.456@COMPUSERVE.COM


Tim Moore                    moore@cs.utah.edu {bellcore,hplabs}!utah-cs!moore
"Ah, youth. Ah, statute of limitations."
		-John Waters