Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!think!barmar
From: barmar@think.com (Barry Margolin)
Newsgroups: comp.lang.lisp
Subject: Re: updating random slots in (say) defstruct
Message-ID: <32964@news.Think.COM>
Date: 18 Jan 90 05:12:52 GMT
References: <18837@bellcore.bellcore.com> <25B37814.3312@marob.masa.com>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 18

In article <25B37814.3312@marob.masa.com> cowan@marob.masa.com (John Cowan) writes:
>	(setf (apply accessor (list instance)) newvalue)

No, this isn't valid.  The first argument to APPLY when it is being used as
a SETF place must be a constant.  SETF is a macro, so it must know at
expansion time what the accessor is so that it can expand into a call to
the corresponding updater.

>(I have not tested it past one implementation.)

If it works, it's due to an implementation extension.  It doesn't work on
my Symbolics system or in Lucid CL; the latter gives the error "SETF of
APPLY is only defined for function args like #'symbol."
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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