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From: jjacobs@well.UUCP
Newsgroups: comp.lang.lisp
Subject: Against the TIde of Common LISP
Message-ID: <2626@well.UUCP>
Date: Sat, 21-Feb-87 22:14:49 EST
Article-I.D.: well.2626
Posted: Sat Feb 21 22:14:49 1987
Date-Received: Sun, 22-Feb-87 10:43:52 EST
References: <2624@well.UUCP>
Reply-To: jjacobs@well.UUCP (Jeffrey Jacobs)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 34


In <6950002@hpfclp.HP.COM>, Chan Benson writes:

>>B.S!  All the compiled code for SET need do is check that the first argument
>>be lexically equivalent to a lexically apparent variable and change
>>the appropriate cell, stack location, or whatever.  Easy for a compiler
>>to do!

>I don't see how it's possible to do this (excuse my potential ignorance).

Let's take a simple example:

(DEFUN FOO (X Y Z) (SET X (CONS Y Z)))

The compiler would have to generate code that would effectively
be equal to

(COND	((EQ X 'X)  (SETQ X (CONS Y Z)))
	((EQ X 'Y)  (SETQ Y (CONS Y Z)))
	((EQ X 'Z)  (SETQ Z (CONS Y Z)))
	(T (SET-SYMBOL-VALUE X (CONS Y Z)))))

i.e. a hidden 'macro-expansion' at compile time.  This should put
to rest assertions that it "can't be done"; it's actually trivial.
(Whether it's desireable or not is another discussion).

 Jeffrey M. Jacobs
 CONSART Systems Inc.
 Technical and Managerial Consultants
 P.O. Box 3016, Manhattan Beach, CA 90266
 (213)376-3802
 CIS:75076,2603
 BIX:jeffjacobs
 USENET: jjacobs@well.UUCP