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Re: Elisp: What does ''nil mean?


From: David Kastrup
Subject: Re: Elisp: What does ''nil mean?
Date: 16 May 2003 13:57:06 +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))?

It is, like (quote nil), the result of evaluating (quote (quote nil)).

> Why would you quote nil and not evaluate it?

To make it different from nil, while evaluating to it eventually.

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

Evaluating nil gives the same result as evaluating (quote nil), since
nil is a self-quoting form.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum


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