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From: mps@ntcsd1.UUCP (Michael P. Smith)
Newsgroups: comp.lang.lisp
Subject: NCONC & Functions
Message-ID: <464@ntcsd1.UUCP>
Date: 28 Nov 89 22:19:26 GMT
Reply-To: mps@ntcsd1.UUCP (Michael Smith)
Distribution: na
Organization: Northern Telecom,  Research Triangle Park,  North Carolina
Lines: 28


On both a TI and a Sun (using Sun Common Lisp (lucid)), the following occurs:

	>(DEFUN foo1 () '(a b c))
	>FOO1
	>(foo1)
	>(A B C)
	>(NCONC (foo1) '(d e f))
	>(A B C D E F)
	>(foo1)
	>(A B C D E F)

(DEFUN foo2 () (LIST 'a 'b 'c)) is unaffected in the same situation.

I think I understand what is happening.  NCONC is treating the pointer re-
turned by evaluating (FOO1) just as if it were evaluating a variable FOO1.
But I don't like it.  There is no variable FOO1, and NCONC is in effect re-
defining the function FOO1.

I have been using the rule: don't use destructive operations on data struc-
tures you care about.  Now this turns out to be insufficient.  Is there a
rule regarding when destructive operations can affect the values returned
by functions they are not part of?  I'm told that even FOO2 is affected when
running Franz on a DEC station.

Thanks.

	Mike Smith 	( mps@ntcsd1 | mcnc!ntcsd1!mps )