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Re: How could I modify list element?
From: |
Thierry Volpiatto |
Subject: |
Re: How could I modify list element? |
Date: |
Tue, 09 Dec 2008 18:21:53 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) |
richardeng <richardeng@foxmail.com> writes:
> Hi all,
> setcar/setcdr is not convenient.
> In a long list, ex.
> (setq a '(a b c d e f g))
> I want to change 'e to 'E.
> I need a function: (set-list-elt list old-elt new-elt)
>
> How? translate list to vector, modify, then turn it back???
Hi, you can try that:
,----
| (defun tv-index-elt-list (elm lis)
| "return index of `elm' in `lis'
| `elm' is an element of the list `lis'"
| (let ((n 0)
| (index 0))
| (if (member elm lis)
| (progn
| (dolist (x lis)
| (when (equal x elm)
| (setq index n))
| (setq n (+ n 1)))
| index)
| (error "No element %s in %s" elm lis)))) ; TODO corriger pour CL
|
|
| (defun tv-add-to-list-at-ind (elm lis where)
| "Add `elm' in `lis' at index `where'"
| (let ((cons-list (cons elm lis))
| (appended-list nil))
| (setq appended-list
| (tv-move-element-in-list elm cons-list (+ 1 where)))
| appended-list))
`----
,----
| (setq A '(a b c d e f))
| (a b c d e f)
|
| (setq ind (tv-index-elt-list 'e A))
| 4
|
| (setq A (remove 'e A))
| (a b c d f)
|
| (setq A (tv-add-to-list-at-ind 'E A 4))
| (a b c d E f)
`----
--
A + Thierry Volpiatto
Location: Saint-Cyr-Sur-Mer - France