Emacs Lisp: intersperse

まぁ、こうやって自前で用意しなくてもあるんでしょうが・・・。

• vallog: Emacs Lisp: fold に続いて pair-fold

(defun single? (ls)
  (and (not (null ls))
       (null (cdr ls))))

(defun intersperse (item ls)
  (pair-fold1 #'(lambda (pr acc)
                  (if (single? pr)
                      (cons (car pr) acc)
                      (cons item (cons (car pr) acc))))
              '() (reverse ls)))

ELISP> (intersperse " " '(1 2 3))
(1 " " 2 " " 3)