Elisp: Destructure Binding (seq-setq, seq-let)

By Xah Lee. Date: . Last updated: .
seq-setq

new in emacs 28.3 Emacs 28 (date 2022) (Add macro seq-setq. Earl Hyatt and larsmagne committed on 2021-08-14)

bind a Sequence of values to several variables.

  • If there are more values, they are ignored.
  • If there are more variables, they get nil.
(let (x1 x2)
  (seq-setq (x1 x2) [3 4])
  (message "%s %s" x1 x2))
;; 3 4

(let (x1 x2)
  (seq-setq (x1 x2) (list 3 4))
  (message "%s %s" x1 x2))
;; 3 4
seq-let

bind a Sequence of values to several local variables.

  • If there are more values, they are ignored.
  • If there are more variables, they get nil.
;; example of using seq-let

;; if there are more variables than in sequence, the rest has value of nil
(seq-let (xa xb xc) [1 2]
    (vector xa xb xc))
;; [1 2 nil]

;; if there are less variables than in sequence, the rest sequence is ignored
(seq-let (xa xb) [1 2 3 4 5]
    (vector xa xb))
;; [1 2]