dumb q, how do I mutate (in-place) a list value? set/setq don't seem apt for the job as one cannot (set (list 2) (list 3))

(progn
  (defvar mylist '(2))
  (setq mylist '(3))
  (print mylist))

works for me

btw, what are you going to mutate by (set (list 2) (list 3)) ?

how about doing (set 2 3) ?

😄

I know I know

being in Clojurians Slack I know the benefits of immutability etc 🙂

O_O

but elisp lists are mutable right? your recipe isn't what I'm looking for unfortunately

list SYMBOLS are mutable

list is a list

as I said before, you can try (set 2 3) with the same success

binding a value to another value doesn't make sense at all

btw, what are you trying to do?

I think it can make sense? consider a javascript array you can mutate its length from 10 to 0 and back right?

I don't know JS 🙂

and references to that array will see the latest mutated value, accordingly

>you can mutate its length from 10 to 0 and back right? you can emulate this in elisp by cadr-ing 🙂, but your HAVE to have a symbol which you are trying to bind to a new value (with a reduced len)

And I still can't understand, how (set (list 2) (list 3)) should work?

ok, if you don't like to create new variables, you can use something like

(defun myset (a b)
  (setq a b))

you can do this in elisp too

ok, so I'm asking if there's a readily available function that provides a behavior equivalent to "mutate this whole list setting it to some-other-list"

by means of push/pop, or otherwise

(defvar a '(1 2 3))

(defun mutate-it (coll)
  (setq coll (cdr coll))
  (setq coll (cdr coll))
  (setq coll (cdr coll))
  (push "foo" coll)
  (push "bar" coll)
  (push "baz" coll))

(mutate-it a)

the literate translation

doesn't work

you cannot use setq

I can

(setq a (mutate-it a))

it's not the JS behavior

see last line of my screenshot, I just a

JS has bad behaviour, lol

also, you can use defmacro and do anything you want to

@vemv there's push: https://www.gnu.org/software/emacs/manual/html_node/elisp/List-Variables.html

and pop: https://www.gnu.org/software/emacs/manual/html_node/elisp/List-Elements.html

you have to push onto a variable

(push list-i-want-to-mutate 4)

otherwise just use cons (cons 3 (list 2))

thanks for the pointer

got it finally!

^ that works, but in certain usages I need to (-clone ...) (dash.el library) things first. couldn't figure out exactly why

which is ironical, yep

(defun vemv/bounded-list/insert-at-head! (x bounded-list bound)
  (mutate-to bounded-list (cons x (-clone bounded-list)))
  (mutate-to bounded-list (-take bound (-clone bounded-list)))
  bounded-list)

Just

don't

use

javascript

thank you