Emacs -- 如何用 let 绑定变量替换列表的第 n 个元素 [英] Emacs -- How to replace nth element of a list with a let-bound variable
问题描述
我还没有找到任何示例说明如何在不先添加每个元素(一个-by-one) 与函数 add-to-ordered-list
-- 例如, (add-to-ordered-list 'the-list 'a 1)代码>.这需要随后删除元素——例如,
(delq a the-list)
.该过程的第三步是添加 new 元素——例如,(add-to-ordered-list 'the-list "HELLO-WORLD!" 1)
.由于以下名为 variable-list-example
的函数使用 26 个元素,我正在寻找一种比首先将所有 26 个元素(一对一)添加到基本上为每个元素分配一个位置编号.函数 add-to-ordered-list
使用一个数字赋值,它与标准的 nth
元素方法不同,其中第一个元素的值为 0
,而 add-to-ordered-list
使用 1
的值作为第一个元素.以下是 add-to-ordered-list
文档的链接:http://www.gnu.org/software/emacs/manual/html_node/elisp/List-Variables.html
I have not found any examples of how to replace the nth
element of a list without first adding every element (one-by-one) with the function add-to-ordered-list
-- e.g., (add-to-ordered-list 'the-list 'a 1)
. That requires subsequently deleting the element -- e.g., (delq a the-list)
. The third step in the process is to add the new element -- e.g., (add-to-ordered-list 'the-list "HELLO-WORLD!" 1)
. As the following function named variable-list-example
uses 26 elements, I'm looking for a better way than first adding all 26 elements (one-by-one) to essentially assign each element a position number. The function add-to-ordered-list
uses a number assignment that is one digit different than the standard nth
element approach where the first element has a value of 0
, whereas add-to-ordered-list
uses the value of 1
for the first element. Here is the link to the documentation for add-to-ordered-list
: http://www.gnu.org/software/emacs/manual/html_node/elisp/List-Variables.html
此外,在列表的开头使用组合 '(
似乎可以防止在列表中使用 let-bound 变量——例如,let-bound 变量出现在列表中my-variable
而不是 HELLO-WORLD!
.我发现的唯一解决方法是上述使用 add-to-ordered-list<的示例/code> -- 这是一个冗长的三步过程(即,从一开始就一个接一个添加每个元素).
In addition, using the combination '(
at the beginning of a list seems to prevent using a let-bound variable inside the list -- e.g., the let-bound variable appears in the list as my-variable
instead of HELLO-WORLD!
. The only work-around I have found is the above-mentioned example using add-to-ordered-list
-- which is a lengthy three-step process (i.e., adding each element one-by-one at the outset).
为了解决这两个问题,我正在寻找一些帮助,请替换 the-list
的 17th
元素(这是字母 r
) with my-variable
(即 HELLO-WORLD!
).
To resolve both issues, I am looking for some assistance please to replace the 17th
element of the-list
(which is the letter r
) with my-variable
(which is HELLO-WORLD!
).
(defun variable-list-example ()
(interactive)
(let* (
(my-variable "HELLO-WORLD!")
(the-list '(a b c d e f g h i j k l m n o p q r s t u v w x y z)))
;; replace the 17th element of `the-list` with `my-variable`
(message "Presto -- this is your new list: %s" the-list)
))
<小时>
名单
'(a b c d e f g h i j k l m n o p q r s t u v w x y z)
<小时>
第 n 个元素 -- 备忘单/图例
element 0: a
element 1: b
element 2: c
element 3: d
element 4: e
element 5: f
element 6: g
element 7: h
element 8: i
element 9: j
element 10: k
element 11: l
element 12: m
element 13: n
element 14: o
element 15: p
element 16: q
element 17: r
element 18: s
element 19: t
element 20: u
element 21: v
element 22: w
element 23: x
element 24: y
element 25: z
推荐答案
You need to use setcar
and nthcdr
:
(setcar (nthcdr 17 the-list) my-variable)
更常见的类似 lisp 的方法是使用 广义变量:
The more common-lisp-like approach is to use Generalized Variables:
(setf (nth 17 the-list) my-variable)
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