* Elisp: What does ''nil mean?
@ 2003-05-16 9:00 Thomas Gehrlein
2003-05-16 10:45 ` David Kastrup
0 siblings, 1 reply; 6+ messages in thread
From: Thomas Gehrlein @ 2003-05-16 9:00 UTC (permalink / raw)
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?
Thomas
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Elisp: What does ''nil mean?
2003-05-16 9:00 Elisp: What does ''nil mean? Thomas Gehrlein
@ 2003-05-16 10:45 ` David Kastrup
2003-05-16 11:35 ` Thomas Gehrlein
0 siblings, 1 reply; 6+ messages in thread
From: David Kastrup @ 2003-05-16 10:45 UTC (permalink / raw)
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.
--
David Kastrup, Kriemhildstr. 15, 44793 Bochum
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Elisp: What does ''nil mean?
2003-05-16 10:45 ` David Kastrup
@ 2003-05-16 11:35 ` Thomas Gehrlein
2003-05-16 11:57 ` David Kastrup
2003-05-16 16:34 ` Pascal Bourguignon
0 siblings, 2 replies; 6+ messages in thread
From: Thomas Gehrlein @ 2003-05-16 11:35 UTC (permalink / raw)
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))?
Why would you quote nil and not evaluate it? And if you evaluate it: Isn't nil
the same as (quote nil)?
Thomas
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Elisp: What does ''nil mean?
2003-05-16 11:35 ` Thomas Gehrlein
@ 2003-05-16 11:57 ` David Kastrup
2003-05-16 16:16 ` Thomas Gehrlein
2003-05-16 16:34 ` Pascal Bourguignon
1 sibling, 1 reply; 6+ messages in thread
From: David Kastrup @ 2003-05-16 11:57 UTC (permalink / raw)
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Elisp: What does ''nil mean?
2003-05-16 11:57 ` David Kastrup
@ 2003-05-16 16:16 ` Thomas Gehrlein
0 siblings, 0 replies; 6+ messages in thread
From: Thomas Gehrlein @ 2003-05-16 16:16 UTC (permalink / raw)
David Kastrup <dak@gnu.org> writes:
> 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.
Thank you. I think now I understand.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Elisp: What does ''nil mean?
2003-05-16 11:35 ` Thomas Gehrlein
2003-05-16 11:57 ` David Kastrup
@ 2003-05-16 16:34 ` Pascal Bourguignon
1 sibling, 0 replies; 6+ messages in thread
From: Pascal Bourguignon @ 2003-05-16 16:34 UTC (permalink / raw)
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))?
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/
----------------------------------------------------------------------
Do not adjust your mind, there is a fault in reality.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2003-05-16 9:00 Elisp: What does ''nil mean? Thomas Gehrlein
2003-05-16 10:45 ` David Kastrup
2003-05-16 11:35 ` Thomas Gehrlein
2003-05-16 11:57 ` David Kastrup
2003-05-16 16:16 ` Thomas Gehrlein
2003-05-16 16:34 ` Pascal Bourguignon
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