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

seq-setq

new in emacs 28.3 (~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]