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From: lou@atanasoff.rutgers.edu (Lou Steinberg)
Newsgroups: comp.lang.lisp
Subject: Re: PLet
Message-ID: <Jan.9.12.33.07.1990.8200@atanasoff.rutgers.edu>
Date: 9 Jan 90 17:33:14 GMT
References: <509@cs.columbia.edu> <1515@skye.ed.ac.uk> <Jan.9.12.12.01.1990.8181@atanasoff.rutgers.edu>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 22
To: lou@atanasoff.rutgers.edu, jeff@aiai.ed.ac.uk

Oops - I let my message get away before I had fixed a mistake at the
end...  Let's try that again.  Here is the corrected ending:

Note that we hash on the "whole" rather than the argument ("form")
because the argument might be just a symbol, which might also be the
argument of some other call to this macro.  However, even this
approach can be wrong - the "whole" can be eq in two different macro
calls if the whole itself comes from a constant in another macro.
E.g.:
<cl> (defmacro foo (x) `(cons ,macro-stuff (1+ ,x)))
<cl> (defmacro fie (x) `(cons ,macro-stuff (1- ,x)))
<cl> (setq macro-stuff '(eval-once *x*))

<cl> (let ((*x* 1)) (foo 10))
(1 . 11) 
<cl> (let ((*x* 2)) (fie 10))
(1 . 9) 
-- 
					Lou Steinberg

uucp:   {pretty much any major site}!rutgers!aramis.rutgers.edu!lou 
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