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Re: [External] : Re: Appending lists
From: |
Jean Louis |
Subject: |
Re: [External] : Re: Appending lists |
Date: |
Mon, 21 Jun 2021 00:46:01 +0300 |
User-agent: |
Mutt/2.0.7+183 (3d24855) (2021-05-28) |
* Emanuel Berg via Users list for the GNU Emacs text editor
<help-gnu-emacs@gnu.org> [2021-06-20 23:43]:
> Actually `append' can also be trouble because the last list
> isn't copied, the new list just has a cdr somewhere to it -
> yes, to the actual list.
>
> Try this:
>
> (setq list-head '(1)) ; (1)
>
> (setq list-tail '(2 3 4)) ; (2 3 4)
>
> (setq whole-list (append list-head list-tail)) ; (1 2 3 4)
>
> (setcdr list-tail '(3.5 4)) ; (3.5 4)
>
> whole-list ; (1 2 3.5 4)
>
> See that "whole-list" changed even tho we did it with `setq',
> append, and didn't mention it...
I see. I wonder if there are some implications in my code. Though
I never used `setcdr' in that combination (or never).
Maybe this is the way to go:
(setq list-head '(1)) ⇒ (1)
(setq list-tail '(2 3 4)) ⇒ (2 3 4)
(setq whole-list (append list-head (copy-sequence list-tail))) ⇒ (1 2 3 4)
(setcdr list-tail '(3.5 4)) ⇒ (3.5 4)
whole-list ⇒ (1 2 3 4)
--
Jean
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- Re: [External] : Re: Appending lists, (continued)
- Re: [External] : Re: Appending lists, Jean Louis, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists, Jean Louis, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists, Jean Louis, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists,
Jean Louis <=
- Re: [External] : Re: Appending lists, Stefan Monnier, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20
- Re: [External] : Re: Appending lists, Emanuel Berg, 2021/06/20