GNU bug report logs - #62068
29.0.60; map-elt and map-insert for nested structures

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From: Augusto Stoffel <arstoffel <at> gmail.com>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: "Basil L. Contovounesios" <contovob <at> tcd.ie>, 62068 <at> debbugs.gnu.org
Subject: bug#62068: 29.0.60; map-elt and map-insert for nested structures
Date: Fri, 10 Mar 2023 08:09:29 +0100

On Fri, 10 Mar 2023 at 02:18, Michael Heerdegen wrote:

> Augusto Stoffel <arstoffel <at> gmail.com> writes:
>
>> I would like to suggest the following two functions to deal with nested
>> maps.  Let me know if you would like to see a patch.
>>
>> (defun map-elt-in (map keys &optional default)
>>   "Look up a nested sequence of KEYS in MAP and return its associated value.
>> KEYS is any sequence type supported by `seq'.  If a key is not
>> found in any intermediate step, return DEFAULT, which defaults to
>> nil."
>>   (catch 'map--break
>>     (seq-reduce (lambda (m k)
>>                   (let ((v (map-elt m k 'map--default)))
>>                     (if (eq v 'map--default)
>>                         (throw 'map--break default)
>>                       v)))
>>                 keys
>>                 map)))
>
> Isn't this more or less the same as `map-nested-elt'?

How did I miss that?  In any case the more interesting bit is the other
function, which should then be renamed to `map-nested-insert'.

Now, `map-nested-elt' has an inconsistency regarding the DEFAULT
argument which needs to be fixed.

(map-nested-elt '(a nil) '(a) 1)
1
(map-nested-elt '((a . nil)) '(a) 1)
1
etc.

While in the other hand:
(map-elt '(a nil) 'a 1)
nil
(map-elt '((a . nil)) 'a 1)
nil
etc.

Also inconsistent with the rest of Emacs:
(let ((m (make-hash-table)))
  (puthash 'a nil m)
  (gethash 'a m 1))
nil
(alist-get 'a '((a . nil)) 1)
nil

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