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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 <thomas.gehrlein@t-online.de> writes:
> David Kastrup <dak@gnu.org> writes:
>
> > Thomas Gehrlein <thomas.gehrlein@t-online.de> 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