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From: jjacobs@well.UUCP
Newsgroups: comp.lang.lisp
Subject: Special Variables in Common LISP
Message-ID: <2625@well.UUCP>
Date: Sat, 21-Feb-87 22:12:24 EST
Article-I.D.: well.2625
Posted: Sat Feb 21 22:12:24 1987
Date-Received: Sun, 22-Feb-87 10:43:38 EST
References: <2624@well.UUCP>
Reply-To: jjacobs@well.UUCP (Jeffrey Jacobs)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 42


In <145@lmi-angel.UUCP>, Bob Krajewski writes:

>In other words, why would anybody do

> (let ((lose-p nil))
>   (save-the-world))

>unless LOSE-P was a special variable which evidently affected the behavior
>of the SAVE-THE-WORLD function ?  If the variable LOSE-P were not special,
>the compiler would probably warn about the useless binding.

Let me change the example a little bit; let's make it

(DEFVAR LOSE-P NIL)

(DEFUN NOT_SURE_YET (LOSE-P) (SAVE-THE-WORLD))

Possible reasons for this:

1.  NOT_SURE_YET isn't completely defined, yet.  

2.  It is anticipated that NOT_SURE_YET might, in the future, need to
change the value of LOSE-P.

3.  It is a primary function of a package, such as an editor,
with LOSE-P the key global variable.  Think of calling a structure
editor with the form to be edited.

Remember that the domain under discussion is that of debugging
*other* people's code, not reading people's code for interest
or fun.  If they were writing reasonable code, I wouldn't have
to be debugging it :-)

 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