Questions tagged [list]

is for the list object in Lisp programming. A list represents a sequence of zero or more elements. Emacs Lisp relies extensively on the list data structure; it is a fundamental building block. Emacs provides many facilities for building, modifying, extending, and efficiently handling list data structures.

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3answers
231 views

When is it better to use the backquote, `(…), and when to use (list …)?

The docstring for quote says, Quoting should be reserved for constants that will never be modified by side-effects, unless you like self-modifying code. Are there cases in which it is the best ...
3
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1answer
74 views

What is the difference between these two lists?

I'm reading An Introduction to Programming in Emacs Lisp by Robert J. Chassell. When the book is introducing setcar, it points out that when we use this function to a list, the list should be ...
3
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2answers
227 views

What difference does it make changing the order of arguments to 'append'

I want to understand the implications of append's property that "All arguments except the last one are copied, so none of the arguments is altered." (from the Elisp manual) Say I have a list ...
2
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2answers
53 views

How to add a string at nth position of an ordered list of strings

The built-in function add-to-ordered-list is for symbols, not strings. I have a list of strings and need to add another string to the list at a specific nth position. How can I accomplish this? TASK:...
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1answer
19 views

Access strange list data

I'm trying to parse the output of ledger-context-at-point for the account name. The output looks something like: (acct-transaction account ((indent " " 238117) (status nil nil)...
3
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3answers
46 views

Retrieve alist from list of alists by value of specific key inside of it

I'm probably missing something simple here but... I've got a list of alists parsed from JSON using json-parse-string. The list of alists is like the following (details omitted for brevity): ( ((id . 1)...
2
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2answers
85 views

Assoc in a nested alist

I have the following nested alist: (setq x '(foo . ((bar . ((chocolate . "edible") (gold . "inedible"))) (jar . "glass")))) How can get entry (chocolate ...
0
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0answers
31 views

How can I add list arguments to key value pairs to defmacro?

I'm trying to use rg. There is this explanation here: (defmacro rg-define-search (name &rest args) "Define an rg search functions named NAME. ARGS is a search specification that defines ...
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3answers
66 views

Replace element in a list / add in case of absence, with custom test/key functions

add-to-list doesn't refresh item, it only checks for existence of item by equal or custom comparison function: (add-to-list 'tramp-methods '("gssh" (tramp-login-program "gcloud ...
1
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1answer
33 views

Function like `setcar` that doesn't change the value of the input function?

Early beginner here. I'm looking for a function that takes a list and changes only its first element, using some function or other. I realize setcar sort of does that, but it also changes the initial ...
3
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3answers
196 views

How to replace an element of a list?

Is there a way to replace an item in a list? (replace-element-in-list (elem-src elem-dst ls &optional times comparison-fn)) ;; ... ) Example use: (replace-element-in-list 1 100 '(3 2 1)) => ...
3
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1answer
40 views

How to add a value after a given value in parts of a list, returning a new list?

I have the following structure: '((a (1 2 3 4)) (b (1 2)) (c (1 3 4 5)) I want to return a new list that's similar, but that has a 7 inserted after each 2: '((a (1 2 7 3 4)) (b (1 2 7)) (c (1 ...
3
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1answer
130 views

How to map or iterate over a list of files and set the result to `org-agenda-files`?

looking for a little help with my function. I'm trying to create a loop-while that'll return a list of files back to org-agenda-files. It's just not working though and i keep getting errors. Any ideas ...
0
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2answers
88 views

Filter list by regexps

How can I get all elements of a list which don't match multiple patterns? The patterns are given as a list. For instance, I want all files without '("no" "nix") in them. (setq se-...
1
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2answers
330 views

Is there a way to spread a list like in Typescript or Golang?

I have a variable with some common values between dap-mode debug templates and I want to use that variable along with other cons elements for :environment-variable in languages like Golang or ...
0
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3answers
161 views

How to replace a list within a list?

What would be the an efficient/concise way to replace a sub-list with another list? Example function call: (replace-list-list-with-list '("A" "B" "C" "D") '("B" "C") '("NEW" "TEXT")) Would result ...
2
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1answer
37 views

Why does Flycheck complain “mapcar called for effect” when my function returns the result of mapcar by design?

Since installing Flycheck I've been bombarded with complaints about the elisp functions I've used reliably for years. This is the first one I can't understand. Here my function is designed to return ...
3
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1answer
120 views

How does a list end in nil?

I believe Emacs lists have nil at their end. That said, I was trying to test examples. Can anyone tell the difference between a and b? (setq a '(foo)) (setq b '(foo nil)) ;; Returns nil and (nil)...
0
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1answer
39 views

Print matching strings line by line

I was trying to use this code shared by @JordonBiondo over here to collect regex matches in a list. (defun matches-in-buffer (regexp &optional buffer) "return a list of matches of REGEXP in ...
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0answers
41 views

Emacs freezes when using split-string in recursive function

I'm trying to figure out why my emacs keeps freezing when running this set of functions to split a string into a list of pairs. Is there some significant overhead happening when using string-split? Is ...
1
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2answers
195 views

Get first n elements of a list

How can I get the first N elements of a list? I know I can use subseq: (subseq '("one" "two" "three" "four" "five") 0 2) Yet when I use subseq, it produces one of the following results: on the ...
1
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1answer
43 views

Would (cycle-list <ls>) be a bad idea?

Would you consider something like this a bad practice? (defun cycle-list (ls &optional backward?) "Given any list, returns the next element each time it is called." (let* ((last-pos (- (...
4
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1answer
222 views

Circular list use of “#”

Looking at this, I see (setq x '#1=(a #1#)) but this evaluates to (a #0). As I understand, this should be (a #1=(a #1#)). But then what syntax makes #0 mean #1=(a #1#)? In general what is # doing in ...
2
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1answer
38 views

Make forward-list search for specific symbol only

Is there a way to make forward-list and backward-listsearch for specific symbols (such as 「」『』) only? I have code that make use of these functions to iterate through 「」『』 pairs in plain text. But ...
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2answers
200 views

How to subtract 1 from the nth element of a list of numbers?

How do I subtract 1 from the second element of the list (3 6)? (setq x '(3 6)) (- (nth 1 x) 1) The above quote does the math but does not return a modified list.
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2answers
51 views

Add a number to every item in list

How do I add a number, say 2, to every item in a list? (setq x '(1 2)) (+ 2 x) (mapcar '2+ x) (loop for i in x do (+ 2 i)) (dolist (i x) (+ 2 i)) None of the above work.
3
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3answers
324 views

Move point inwards while counting number of nested parentheses without throwing an error

I would like to write a function that counts the number of nested parentheses while moving the cursor to the innermost bracket without throwing an error. (defun count-and-move () (interactive) ...
2
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5answers
542 views

Remove multiple elements from a list

Given '(a b c d), how would I remove b and c to end up with '(a d)? Is there a "right" way to remove multiple, distinct elements from a list? Obviously, one could do (delete 'c (delete 'b '(a b c d))...
3
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2answers
178 views

Apply different function to each element in list?

I have a time-stamp of a video formatted as "00:00:00,000" such that "%H:%M:%s,%3N". I am want to eventually use this timestamp as part of an in-interval-p function where I take two timestamps and a ...
1
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2answers
43 views

How to check if a list ends with another list?

Currently I'm using a fairly inefficient way to check if one list uses another list at it's end. Is there a more efficient way to do this? (defun is-in-list (ls-haystack ls-ends-with) (catch 'found ...
3
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2answers
438 views

How to check if two lists share any elements?

Besides looping over list items and comparing, what is a good way in elisp to check if there are any shared items between two lists? For example, in Python this can be done with sets or list ...
1
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1answer
59 views

Is function `list` equivalent to using `cons` with a final cdr of `nil`?

I'm trying to explain Elisp to 5th and 6th graders and I tell them that (+ 1 2) evaluates to 3 and not (3). So if I do want something that evaluates to (3) would I just evaluate ((+ 1 2))? No! This ...
3
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1answer
4k views

Melpa - 'Failed to download melpa'

I am on a fresh install of emacs 26.3, and I have the following in my init.el: (require 'package) (add-to-list 'package-archives '("melpa", "http://melpa.org/packages/") t) (package-...
0
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2answers
63 views

Representing leading zeroes in a list

I would like to have this table #+NAME: addition-table | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |---+----+----+----+----+----+----+----+----+----+----| | 0 | 00 | 01 | 02 | 03 | 04 | ...
5
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1answer
718 views

Are the graphical depictions in docs drawed in manual labour?

There are tons of pretty graphical depictions in the emacs(or elisp) docs such as x1: -------------- -------------- -------------- | car | cdr | | car | cdr | | car | ...
1
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1answer
110 views

Map each element of a list over every element of another list

Let's assume I've got two lists: ("A" "B" "C" "D") and ("+" "-"). I want to concatenate each element of the first list with every element of the second to get ("A+" "A-" "B+" "B-" ... ). Is there a ...
0
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1answer
43 views

Inline elements of variable list value in rx() macro call [duplicate]

Is there a more compact way to make use of the rx macro in cases where we want to inline a list of strings from a variable? Such as (defconst c++20-new-keywords-list (list "char8_t" "import" ...
2
votes
1answer
195 views

Elisp: How to accumulate function return into a list

I have this small snippet of Elisp code that decodes kernel traces: (defvar projbase "/my/proj/base") (setq my_shell_output (substring (shell-command-to-string (concat "/home/demetra/scripts/...
1
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2answers
165 views

Orgmode automatically increment an unordered list

I use org-mode for planning projects and tasks, etc. Say I am reading a book and I want to track my progress chapter by chapter. I want to create a list of repetitive elements with an incremented ...
2
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1answer
70 views

trying to make a self-modifying function [duplicate]

I'm trying to make a function that returns a list of perfect numbers: A perfect number is a positive integer that is equal to the sum of its proper positive divisors For instance, 28 is perfect ...
7
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3answers
652 views

Removing the last element of a list

Is there a simpler way to remove the last element of a list than this? (setq list (reverse (cdr (reverse list))))
6
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1answer
178 views

Shortening trees list with (setcdr (nthcdr 2 trees) nil)

I am starting to learn elisp and working through this tutorial https://www.gnu.org/software/emacs/manual/html_node/eintr/kill_002dnew-function.html and I do not understand this basic example: (setq ...
1
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1answer
58 views

midnight-mode add-to-list Format specifier doesn't match argument type

I've been trying to get midnight-mode to add to the following list. I have a feeling it has to do with an elisp error in my config I'm not seeing. It works fine with setq, but with add-to-list I get a ...
2
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1answer
264 views

How to write a list literal with conditional items? [duplicate]

Given a list literal '(1 2 3) is it possible to conditionally include parts of the list? eg: '(1 2 3 (when thing-is-true '(10 11 12))) 4 5 6) Which would result in '(1 2 3 4 5 6) or '(1 2 3 ...
3
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1answer
660 views

Org Mode. Set separation length between elements of a list

I have noticed there is a big gap between the elements of a list when exporting to PDF. Is there a way to modify it?
0
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1answer
69 views

List variable that is set to one list or another depending on condition

I am trying to create a list variable that can be set to one list or another depending on a condition. What I have so far is as follows. (let ((l (if local list1 list2))) ; Append items to the list ...
0
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1answer
51 views

How can i add same value to every item in list, turning it into alist?

I tried to use this code, but it returns (k k k k k) (mapcar (lambda (x) 'cons x '(k)) '(a b c d e)) What am i doing wrong here? Why doesn't cons work?
4
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4answers
613 views

Map function onto nested list?

Q: how can I map a function onto elements of nested lists? For flat lists, we can use mapcar to apply a function to each element of the list: (setq flat '("kittens" "puppies" "otters" "bunnies")) (...
9
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1answer
728 views

When to use quote for lists? Modifying quoted lists in Elisp

The Common Lisp Hyper Spec says: The consequences are undefined if literal objects (including quoted objects) are destructively modified. This is further motivated at the Constant Modification ...
2
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2answers
203 views

Evaluating symbol in function arguments affected by destructive operations?

While evaluating a function call, the arguments is from left to right. For example, (let ((x '(1 2 3))) (list (nreverse x) x)) ;; => ((3 2 1) (1)) The first argument (nreverse x) evaluates to (...