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Message from discussion I never realized the funny difference between nil and () before.
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Kaz Kylheku  
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 More options Nov 2 2011, 1:16 pm
Newsgroups: comp.lang.lisp
From: Kaz Kylheku <k...@kylheku.com>
Date: Wed, 2 Nov 2011 17:16:12 +0000 (UTC)
Local: Wed, Nov 2 2011 1:16 pm
Subject: Re: I never realized the funny difference between nil and () before.
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On 2011-11-01, jimka <ji...@rdrop.com> wrote:

> I got this excerpt from Common Lisp the Language, 2nd Edition
> http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node9.html#SECTION00522...

> An empty list may ... be written (); this normally denotes the same
> object as nil.
> (It is possible, by extremely perverse manipulation of the package
> system, to cause the sequence of letters nil to be recognized not as
> the symbol that represents the empty list but as another symbol with
> the same name.)

Forgetting to bring in symbols from the :cl package is hardly perverse,
let alone extremely perverse:

[1]> (defpackage :my-package (:use))
#<PACKAGE MY-PACKAGE>
[2]> (in-package :my-package)
#<PACKAGE MY-PACKAGE>
MY-PACKAGE[3]> nil

*** - SYSTEM::READ-EVAL-PRINT: variable NIL has no value
The following restarts are available:
USE-VALUE      :R1      Input a value to be used instead of NIL.
STORE-VALUE    :R2      Input a new value for NIL.
ABORT          :R3      Abort main loop


 
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