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Re: Elisp: What does ''nil mean?


From: Pascal Bourguignon
Subject: Re: Elisp: What does ''nil mean?
Date: 16 May 2003 18:34:25 +0200
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50

Thomas Gehrlein <address@hidden> writes:

> David Kastrup <address@hidden> writes:
> 
> > Thomas Gehrlein <address@hidden> writes:
> > 
> > > The following line is from easy-menu-create-menu:
> > > 
> > > ((eq keyword :active) (setq enable (or arg ''nil)))
> > > 
> > > It is part of a (cond ...).
> > > 
> > > What does "''nil" mean?
> > 
> > The same as '(quote nil), an unevaluated list with the two members
> > quote and nil.
> 
> Is this the same as (quote (quote nil))?

Yes.

 
> Why would you quote nil and not evaluate it?  And if you evaluate
> it: Isn't nil the same as (quote nil)?

Just try it!

(show (car ''nil))   | (show (car 'nil))   | (show (car nil))  
==> quote            | ==> nil             | ==> nil           
(show (cdr ''nil))   | (show (cdr 'nil))   | (show (cdr nil))  
==> (nil)            | ==> nil             | ==> nil           
                                        

-- 
__Pascal_Bourguignon__                   http://www.informatimago.com/
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Do not adjust your mind, there is a fault in reality.


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