Subject: bug#75170: add-to-alist: new function

From: Robert Pluim <[email-masked]>
Date: Tue, 21 Jan 2025 10:35:02 +0100

>>>>> On Tue, 21 Jan 2025 03:12:43 -0600, Stefan Kangas <[email-masked]> said:

    Stefan> "Alfred M. Szmidt" <[email-masked]> writes:
    >> map-put! does not work well with alists that are not 'proper':
    >> 
    ELISP> (setq x (list 1 '(2 . 3)))
    >> (1 (2 . 3))
    >> 
    >> Why should it work on alists at all?  map-put! assumes a map (where is
    >> this structure documented? I did not see anything in the Elisp
    >> manual), not an alist.  Invalid alists will also not work on functions
    >> that assume alists.

"invalid alists" is not something that Emacs really cares about:

ELISP> (setq y '(1 (2 . 4) 3))
(1 (2 . 4) 3)

ELISP> (assoc 2 y)
(2 . 4)

ELISP> (setf (alist-get 2 y) 66)
66
 (#o102, #x42, ?B)
ELISP> (assoc 2 y)
(2 . 66)

ELISP> y
(1 (2 . 66) 3)

    Stefan> According to M-x describe-package RET map RET:

    Stefan> map.el provides generic map-manipulation functions that work on
    Stefan> alists, plists, hash-tables, and arrays.  All functions are
    Stefan> prefixed with "map-".

Yes. Except that map.el expects alists to be 'proper'.

Robert
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