dolist

spec には head に指定した変数に tail に続くリストを順番に割り当ててループする。

code: subr.el

(defmacro dolist (spec &rest body)

"Loop over a list.

Evaluate BODY with VAR bound to each car from LIST, in turn.

Then evaluate RESULT to get return value, default nil.

(declare (indent 1) (debug ((symbolp form &optional form) body)))

(unless (consp spec)

(signal 'wrong-type-argument (list 'consp spec)))

(unless (<= 2 (length spec) 3)

(signal 'wrong-number-of-arguments (list '(2 . 3) (length spec))))

;; It would be cleaner to create an uninterned symbol,

;; but that uses a lot more space when many functions in many files

;; use dolist.

;; FIXME: This cost disappears in byte-compiled lexical-binding files.

(let ((temp '--dolist-tail--))

;; This test does not matter much because both semantics are acceptable,

;; but one is slightly faster with dynamic scoping and the other is

;; slightly faster (and has cleaner semantics) with lexical scoping.

(if lexical-binding

`(let ((,temp ,(nth 1 spec)))

(while ,temp

(let ((,(car spec) (car ,temp)))

,@body

(setq ,temp (cdr ,temp))))

,@(cdr (cdr spec)))

`(let ((,temp ,(nth 1 spec))

,(car spec))

(while ,temp

(setq ,(car spec) (car ,temp))

,@body

(setq ,temp (cdr ,temp)))

,@(if (cdr (cdr spec))

`((setq ,(car spec) nil) ,@(cdr (cdr spec))))))))

code: dolist.el

(dolist (i '(1 2 3))

(message "i: %s" i))