ELisp: Map, Iteration

Map a Function to Sequence

mapcar

(mapcar FUNCTION SEQUENCE)

• Apply function to each element of Sequence
• Return the result as a list.
• FUNCTION must be a Symbol, or Lambda.

;; apply a lambda to each vector (take 1st element)
(mapcar (lambda (x) (aref x 0)) [[1 2] [3 4] [5 6]])
;; (1 3 5)

;; apply a buildin function named 1+ to each vector element
(mapcar '1+ [0 1 2])
;; (1 2 3)

;; apply a function to list
(mapcar '1+ '(0 1 2))
;; (1 2 3)

mapc (for-each)

mapc

(mapc FUNCTION SEQUENCE)

• Apply function to each element of Sequence
• Return SEQUENCE unchanged.

(mapc
 (lambda (x)
   (insert (number-to-string x)))
 (number-sequence 1 9))

;; insert 123456789

;; apply a file function to a list of files
(mapc 'my-update-footer
      (list "~/x1.html" "~/x2.html" "~/x3.html"))

dolist: Loop Thru a List

dolist

• (dolist (VAR LIST) BODY)
• (dolist (VAR LIST RESULT) BODY)

• Loop over a list.
• Each time eval BODY, with VAR having value of an element in list.
• Return nil or RESULT.
• RESULT is evaluated last.

(let (xx)
  (setq xx (number-sequence 1 5))
  (dolist (n xx)
    (insert (number-to-string n))))

;; inserts 12345
;; return nil

Loop Thru a Sequence

to loop thru a sequence, use seq-doseq

(setq xx [1 2 3] )
(seq-doseq (x xx)
  (message "x is %s" x))
;; return the original sequence [1 2 3]

• ELisp: Sequence Functions