From: Augusto Stoffel <arstoffel@gmail.com>
To: 62068@debbugs.gnu.org
Cc: "Basil L. Contovounesios" <contovob@tcd.ie>
Subject: bug#62068: 29.0.60; map-elt and map-insert for nested structures
Date: Thu, 09 Mar 2023 09:16:30 +0100 [thread overview]
Message-ID: <875ybafig1.fsf@gmail.com> (raw)
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.
--8<---------------cut here---------------start------------->8---
(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)))
--8<---------------cut here---------------end--------------->8---
Examples:
(map-elt-in '(x (y (z 1))) '(x y))
=> (z 1)
(map-elt-in '(x (y (z 1))) '(x y z))
=> 1
(map-elt-in '(x (y (z 1))) '(x y zz))
=> nil
(map-elt-in '(x (y (z 1))) '(x yy zz) 99)
=> 99
--8<---------------cut here---------------start------------->8---
(defun map-insert-in (map keys value &optional default-type)
"Return a new map like MAP except that it the nested KEYS with VALUE.
This does not modify MAP. KEYS is any sequence type supported by
`seq'. If intermediate values are missing, they are created with
DEFAULT-TYPE."
(when (seq-empty-p keys)
(error "Keys sequence must not be empty."))
(named-let recur ((map map) (keys keys))
(let* ((k (seq-first keys))
(ks (seq-rest keys))
(new (if (seq-empty-p ks)
(map-insert map k value)
(map-insert map k (recur (map-elt map k) ks)))))
(if (and (not map) default-type) (map-into new default-type) new))))
--8<---------------cut here---------------end--------------->8---
Examples:
(map-insert-in nil '(x y z) 1)
=> ((x (y (z . 1))))
(map-insert-in nil '(x y z) 1 'plist)
=> (x (y (z 1)))
(map-insert-in '(x 2 y (z 3)) '(y a b) 1 'plist)
=> (y (a (b 1) z 3) x 2 y (z 3))
;; Looks funny, but see bug#62067
next reply other threads:[~2023-03-09 8:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-09 8:16 Augusto Stoffel [this message]
2023-03-10 1:18 ` bug#62068: 29.0.60; map-elt and map-insert for nested structures Michael Heerdegen
2023-03-10 7:09 ` Augusto Stoffel
2023-03-11 3:22 ` Michael Heerdegen
2023-03-11 7:51 ` Augusto Stoffel
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