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.
87
questions
1
vote
2answers
32 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
...
2
votes
2answers
56 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
vote
1answer
36 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 ...
0
votes
1answer
116 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", "https://melpa.org/packages") t)
(package-...
0
votes
2answers
36 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
votes
1answer
714 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
vote
1answer
44 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
votes
1answer
28 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"
...
1
vote
1answer
84 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
vote
2answers
67 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
votes
1answer
56 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 ...
6
votes
1answer
151 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
votes
1answer
149 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
vote
1answer
42 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
votes
1answer
136 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
votes
1answer
212 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
votes
1answer
46 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
votes
1answer
45 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
votes
4answers
345 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"))
(...
6
votes
0answers
291 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
votes
2answers
132 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 (...
2
votes
2answers
105 views
Does `car` on an non-lazy function generated list evals the whole list?
I want to get in a huge directory the first file which satisfies some condition, something like
(require 'seq)
(require 'f)
(defun lazy-filter-file (pred path)
(car (seq-filter pred (f--files path ...
3
votes
2answers
216 views
How to delete all list elements matching a regexp?
Given a list:
(setq mylist '("a1" "a2" "b1" "b2"))
How to delete all elements that match ^a?
What I want is "a1" and "a2" deleted, only left "b1" and "b2" in the list.
2
votes
2answers
52 views
Arbitrary length lists as argument for interactive function
Say I have a defun with a dolist inside that I want to be able to pass a string that is then converted to a list with a length equal to the number of words in said string via the minibuffer, so ...
0
votes
1answer
29 views
Comparing `system-configuration-options` to a user-specified list
In this example, the system-configuration-options is a string:
"--prefix=/Users/HOME/.0.data/.0.emacs/.0.x11 --with-x --with-ns=no --enable-checking=yes,glyphs --enable-check-lisp-object-type --...
1
vote
0answers
94 views
Directed Acyclic Graphs in Emacs Lisp
Emacs Lisp has support for lists (naturally), association lists, and property lists, vectors, and hash tables. Does it have support for directed acyclic graphs (DAGs)?
I have not found a DAG API in ...
0
votes
1answer
87 views
Updating `dired-directory` after renaming a file
Q: I have a list of strings: '("apple" "pear" "peach" "nectarine" "watermelon"). How can I replace "peach" with "plum" and maintain the same order of fruits? [CAVEAT: The list may be very long ...
1
vote
1answer
129 views
Replacing autoref command format specification in auctex's font-latex-match-reference-keywords-local
With some help I have redefined the autoref command to take an optional argument, see https://tex.stackexchange.com/questions/428229/autoref-with-optional-argument-text-in-generated-link
Now I am ...
3
votes
4answers
305 views
How to mapcar uneven lists?
I am aware I can use mapcar to join 2 lists into pairs, however all the map functions seem to quit at the shortest list.
This for example
(cl-mapcar #'concat '("1" "2" "3" "4") '("a" "b" "c"))
...
2
votes
2answers
310 views
Sort list by decreasing length of the strings
I have this list:
(setq MYLIST '("J. Phys."
"New. J. Phys."
"J. Phys. Soc. Jap."
"Phys. Plasmas"))
How can I get a new list ordered by the decreasing ...
3
votes
2answers
601 views
Adding many items to a list
What is the proper way to add many items to a list? I assume just using many add-to-lists is not the normal way?
0
votes
1answer
39 views
cons a symbol with a variable and return as a symbol [duplicate]
How can I make fun2 return as the same as fun1?
(defun fun1 ()
'((hello . "test"))) ; <= returns ((hello . "test"))
(defun fun2 (str)
'((hello . str))) ; <= this is wrong! should return ((...
3
votes
2answers
53 views
How to define a bundle of variable-and-function pairs?
I want to define a bundle of variable-and-function pairs, e.g.: vl/path-doc points to my often used path, and vl/open-path-doc is used for open it in dired-mode.
I tried this piece of code:
(setq ...
0
votes
2answers
377 views
How do I rotate list elements?
Q: how do I rotate the elements of a list such that last becomes first?
Given a list of arbitrary length, how do I rotate the list
non-destructively such that the last element becomes the first
...
1
vote
1answer
206 views
How to pop an arbitrary element from a list?
Q: how do I pop an arbitrary element from a list?
Given the list '(a b c d e), pop returns a and destructively
modifies the list to '(b c d e). How can I generalize this
function so I could pop an ...
1
vote
1answer
58 views
Doubly-linked list package
Are there any good packages for Emacs that implement doubly-linked lists? I know I could make them myself, but I'd rather not re-invent the wheel.
1
vote
3answers
88 views
How can I convert a list of integers to a string?
Let's say I have a list of integers, representing year, month, day for a date:
(2017 8 21)
and I want to format the list in one function call, as in
(format "%04d-%02d-%02d" 2017 8 21)
Is there an ...
2
votes
1answer
422 views
How to sort an association list (alist)?
Is there a way to sort an association list? In my case I would like to sort the alist elements by the values in each list element (represented by the integers in the example below).
Example:
(setq ...
1
vote
1answer
48 views
How to create and traverse a multidimensional list
I have code like this:
(let* ((l1 '(1 2 3))
(l2 '(4 5 6))
(l3 '(7 8 9))
(ml '(l1 l2 l3)))
(dolist (l ml)
(message "%s" l)
(dolist (e l)
(message "%s" e))))
But ...
1
vote
1answer
121 views
How to get the value of :ID: property of a org-contacts-entry in an org-capture-template?
Problem
I want to get the value of a property of a org-contacts-db entry:
\* Example Contact :MYTAG:
:PROPERTIES:
:ID: foobar
:END:
With the function call (org-contacts-filter "Example ...
2
votes
2answers
203 views
Why is the . needed for adding suffixes to the 'auto-mode-alist?
In
https://www.emacswiki.org/emacs/AutoModeAlist
one needs to use this command in order to add .py for python-mode (add-to-list 'auto-mode-alist '("\\.py\\'" . python-mode))
Why do we need the . ...
0
votes
1answer
351 views
how to specify an Cyclic list in lisp?
How to specify a list, which's last element is referring to the first element?
By specify I mean, for example, how to write a setq statement with this list.
I have seen this in the documentation, ...
2
votes
1answer
1k views
How to enable type-check rules with flycheck-tslint
I want flycheck to use the tslint's --type-check flag to compile my typescript files. In order to see unused imports on the fly inside emacs.
By tslint docs
--type-check
Enables the type ...
13
votes
2answers
8k views
How to concatenate two lists?
Sorry, but elisp is not my best.
I need to combine two lists of strings in this way:
("a" "b" "c") + ("d" "e" "f") -> ("a" "b" "c" "d" "e" "f")
Well, the order is not important, so I wrote this ...
0
votes
1answer
73 views
Custom function to map through nested lists sorting by time-stamp
In the following example, please assume that we are using time-to-seconds to convert each times-stamp into a decimal representation. I have already converted the time-stamps to seconds in this ...
5
votes
0answers
142 views
Structure-preserving copying of sequences
The form (cl-copy-tree TREE t) returns a deep-copy of a sequence TREE.
The the Common Lisp Hyper Spec explains that copy-tree does not preserve circularities and sharing of substructures. I.e., even ...
5
votes
1answer
392 views
Add to a list that defcustom has not yet defined
We can avoid adding duplicate elements to a list variable by using add-to-list.
When setting a customizable variable (i.e. one that is or will be defined by defcustom) from our init file, we're ...
7
votes
5answers
546 views
Report duplicates in a list?
Q: how do I get only the duplicate elements in a list?
delete-dups (and cl-delete-duplicates) deletes all duplicate
elements from a list:
(delete-dups '(a b c c d d)) ; => '(a b c d)
...
2
votes
1answer
100 views
Compare all elements of 2 lists, not necessarily in same order
Q: How to test whether all elements of two lists are the same even though the order may be different?
EXAMPLE: (test-fn '(answered cached unread) '(unread answered cached)) => t
2
votes
1answer
137 views
Building a list of strings with a regexp while loop
I'd like to perform a regexp search, capture part of a matched string, and save
that part to a list. (Eventually the plan is to save this list to a file in a
particular format, but for now a simple ...
