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From: weinrich@clarity.Princeton.EDU (Tim Weinrich)
Newsgroups: comp.lang.lisp
Subject: Re: Destructive Operations
Message-ID: <WEINRICH.91Apr26154635@clarity.Princeton.EDU>
Date: 26 Apr 91 19:46:35 GMT
References: <1351@ai.cs.utexas.edu>
Sender: news@idunno.Princeton.EDU
Organization: Cognitive Science Lab.  Princeton University.
Lines: 18
In-reply-to: gideon@cs.utexas.edu's message of 25 Apr 91 03:09:06 GMT


   One point I dont think anyone mentioned is that it is possible to
create self-modifying code in Lisp through perfectly innocent use of
destructive functions, as in:

	(setq a '(some bogus list))
	.
	.
	.
	(rplaca a 'another)

Interestingly, this example is still self-modifying even if you use a
back-quote instead of a quote (at least in the implementations I have
used).  The back-quoter is "intelligent" enough to act like a QUOTE
(rather than a LIST) if there is nothing in the list to be evaluated.


   Twinerik