* setcdr question
@ 2013-07-01 22:46 drain
2013-07-02 2:12 ` Pierre Lorenzon
2013-07-02 9:06 ` Nicolas Richard
0 siblings, 2 replies; 9+ messages in thread
From: drain @ 2013-07-01 22:46 UTC (permalink / raw)
To: Help-gnu-emacs
(setq list '(Trevor Jason John Alex Max))
(setcdr (nthcdr (1- 4) list) 'Christina)
list
"list" is now set to:
(Trevor Jason John Alex . Christina)
Why is the dot there?
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* Re: setcdr question
2013-07-01 22:46 setcdr question drain
@ 2013-07-02 2:12 ` Pierre Lorenzon
2013-07-02 9:06 ` Nicolas Richard
1 sibling, 0 replies; 9+ messages in thread
From: Pierre Lorenzon @ 2013-07-02 2:12 UTC (permalink / raw)
To: aeuster; +Cc: Help-gnu-emacs
From: drain <aeuster@gmail.com>
Subject: setcdr question
Date: Mon, 1 Jul 2013 15:46:10 -0700 (PDT)
> (setq list '(Trevor Jason John Alex Max))
>
> (setcdr (nthcdr (1- 4) list) 'Christina)
>
> list
>
> "list" is now set to:
>
> (Trevor Jason John Alex . Christina)
>
> Why is the dot there?
Because you should have issued :
(setcdr (nthcdr (1- 4) list) '(Christina))
See how lists are made from cons cell. The cdr should always
be a list itself or nil at the end.
Regards
Pierre
>
>
>
> --
> View this message in context: http://emacs.1067599.n5.nabble.com/setcdr-question-tp290941.html
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>
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* Re: setcdr question
2013-07-01 22:46 setcdr question drain
2013-07-02 2:12 ` Pierre Lorenzon
@ 2013-07-02 9:06 ` Nicolas Richard
2013-07-02 9:17 ` Teemu Likonen
1 sibling, 1 reply; 9+ messages in thread
From: Nicolas Richard @ 2013-07-02 9:06 UTC (permalink / raw)
To: drain; +Cc: Help-gnu-emacs
drain <aeuster@gmail.com> writes:
> (setq list '(Trevor Jason John Alex Max))
> (setcdr (nthcdr (1- 4) list) 'Christina)
As your question was already answered, I allow me to digress slightly
in suggesting that you may like setf for such operations:
(let ((list '(Trevor Jason John Alex Max)))
(setf (nth (1- 4) list) 'Christina)
list)
=> (Trevor Jason John Christina Max)
--
Nico.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: setcdr question
2013-07-02 9:06 ` Nicolas Richard
@ 2013-07-02 9:17 ` Teemu Likonen
2013-07-02 22:17 ` drain
0 siblings, 1 reply; 9+ messages in thread
From: Teemu Likonen @ 2013-07-02 9:17 UTC (permalink / raw)
To: Nicolas Richard; +Cc: drain, Help-gnu-emacs
[-- Attachment #1: Type: text/plain, Size: 553 bytes --]
Nicolas Richard [2013-07-02 11:06:58 +02:00] wrote:
> drain <aeuster@gmail.com> writes:
>> (setq list '(Trevor Jason John Alex Max))
>> (setcdr (nthcdr (1- 4) list) 'Christina)
> (let ((list '(Trevor Jason John Alex Max)))
> (setf (nth (1- 4) list) 'Christina)
> list)
In Common Lisp a literal data shouldn't be edited. I suggest adopting
the same practice in Emacs Lisp too. So, create your list with LIST
(list 'Trevor 'Jason 'John 'Alex 'Max)
or copy a literal sequence before editing:
(copy-sequence '(Trevor Jason John Alex Max))
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^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: setcdr question
2013-07-02 9:17 ` Teemu Likonen
@ 2013-07-02 22:17 ` drain
2013-07-02 22:26 ` drain
` (2 more replies)
0 siblings, 3 replies; 9+ messages in thread
From: drain @ 2013-07-02 22:17 UTC (permalink / raw)
To: Help-gnu-emacs
Appreciate the answers.
However, where is the dot coming from? What is that supposed to represent?
--
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* Re: setcdr question
2013-07-02 22:17 ` drain
@ 2013-07-02 22:26 ` drain
2013-07-03 9:13 ` Pierre Lorenzon
[not found] ` <mailman.90.1372804018.12400.help-gnu-emacs@gnu.org>
2 siblings, 0 replies; 9+ messages in thread
From: drain @ 2013-07-02 22:26 UTC (permalink / raw)
To: Help-gnu-emacs
Ignore. Figured out.
That was pure laziness; apologies.
--
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* Re: setcdr question
2013-07-02 22:17 ` drain
2013-07-02 22:26 ` drain
@ 2013-07-03 9:13 ` Pierre Lorenzon
[not found] ` <mailman.90.1372804018.12400.help-gnu-emacs@gnu.org>
2 siblings, 0 replies; 9+ messages in thread
From: Pierre Lorenzon @ 2013-07-03 9:13 UTC (permalink / raw)
To: aeuster; +Cc: Help-gnu-emacs
From: drain <aeuster@gmail.com>
Subject: Re: setcdr question
Date: Tue, 2 Jul 2013 15:17:11 -0700 (PDT)
> Appreciate the answers.
>
> However, where is the dot coming from? What is that supposed to represent?
A cons cell : (cons 'a 'b) => (a . b)
Regards
Pierre
>
>
>
> --
> View this message in context: http://emacs.1067599.n5.nabble.com/setcdr-question-tp290941p291014.html
> Sent from the Emacs - Help mailing list archive at Nabble.com.
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: setcdr question
[not found] ` <mailman.90.1372804018.12400.help-gnu-emacs@gnu.org>
@ 2013-07-03 13:04 ` Rustom Mody
2013-07-04 19:19 ` drain
0 siblings, 1 reply; 9+ messages in thread
From: Rustom Mody @ 2013-07-03 13:04 UTC (permalink / raw)
To: help-gnu-emacs
On Wednesday, July 3, 2013 3:56:54 AM UTC+5:30, drain wrote:
> Ignore. Figured out.
> That was pure laziness; apologies.
Asking this question is the initiatory rite of starting lisp :-)
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: setcdr question
2013-07-03 13:04 ` Rustom Mody
@ 2013-07-04 19:19 ` drain
0 siblings, 0 replies; 9+ messages in thread
From: drain @ 2013-07-04 19:19 UTC (permalink / raw)
To: Help-gnu-emacs
Things really open up once car / cons / cdr / nth / nthcdr are properly
understood.
I had so much inefficient code before!
Emacs über alles.
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end of thread, other threads:[~2013-07-04 19:19 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-07-01 22:46 setcdr question drain
2013-07-02 2:12 ` Pierre Lorenzon
2013-07-02 9:06 ` Nicolas Richard
2013-07-02 9:17 ` Teemu Likonen
2013-07-02 22:17 ` drain
2013-07-02 22:26 ` drain
2013-07-03 9:13 ` Pierre Lorenzon
[not found] ` <mailman.90.1372804018.12400.help-gnu-emacs@gnu.org>
2013-07-03 13:04 ` Rustom Mody
2013-07-04 19:19 ` drain
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