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From: mlittman@BREEZE.BELLCORE.COM (Michael L. Littman)
Newsgroups: gnu.emacs.bug
Subject: Backquote results in different behavior when byte-compiled
Message-ID: <9010091456.AA18404@breeze.bellcore.com>
Date: 9 Oct 90 14:56:40 GMT
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System: Sparc 18.55

 I am using a macro to generate a list which I then tamper with using
"setcar".  Before I byte-compile, "setcar" does not produce a
side-effect to the macro.  After I compile, it does.

 If I define the macro any other way, I get consistent results: either
"setcar" produces side-effects in the compiled version AND the
uncompiled version, or it "setcar" produces no side-effects in the
compiled version OR the uncompiled version.

; Program:

(defmacro nil-list ()
  (` (cons '(nil) nil)))

(defun change-nils (true)
  (let ((a (nil-list)))
    (if true
	(setcar (car a) 'up)
      )
    a))

; Test...

(change-nils t)  =>  ((up))
(change-nils nil) => ((nil))	; No side effect
(byte-compile 'change-nils)
(change-nils t) =>   ((up))
(change-nils nil) => ((up))	; Side effect

-Michael