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From: notes@iuvax.UUCP
Newsgroups: net.emacs
Subject: Re: Parameters and recursion - (nf)
Message-ID: <318@iuvax.UUCP>
Date: Wed, 11-Apr-84 01:02:39 EST
Article-I.D.: iuvax.318
Posted: Wed Apr 11 01:02:39 1984
Date-Received: Thu, 12-Apr-84 04:45:42 EST
Sender: notes@iuvax.UUCP
Organization: Indiana University
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#R:uo-vax1:-1020000200:iuvax:2300005:000:820
iuvax!unix68    Apr 10 18:22:00 1984

I remember figuring this one out when I first started writing mlisp code.
The reason for the behaviour is that the passed arguments are not
evaluated until the called function actually asks for them to be
evaluated and they are then evaluated in the CALLED function's current
environment rather than the CALLING function's environment.

Since bar is a local variable, when (setq bar (arg 1 "bar? "))
is executed the second time, bar is 'lambda bound' to 0, and
(arg 1 "bar? ") is the value of (- bar 1) IN THE CURRENT ENVIRONMENT
RATHER THAN THE CALLING ENVIRONMENT and is thus equivalent to
(- 0 1) or -1.

I don't know whether this is considered a 'bug' or a 'feature', but
I think that this is one of the things that got changed (to work the
way you would expect) when the new, alternative, defun syntax was
created.