elisp-demo-03.el

elisp-demo-03.el

;; List -- car/cdr/nthcdr/nth
(defvar my-list '(a b c) "My demo LIST")
my-list

(car my-list)
a

(cdr my-list)
(b c)

(cons 'a '(b c))
(a b c)

(length my-list)
3

(length ())
0

(nthcdr 0 my-list)
(a b c)

(nthcdr 1 my-list)
(b c)

(nthcdr 2 my-list)
(c)

(nthcdr 3 my-list)
nil

(defun my-nthcdr (n a-list)
  "Implement nthcdr"
  (while (> n 0)
    (setq n (1- n))
    (setq a-list (cdr a-list)))
  (message "%S" a-list))

(my-nthcdr 0 my-list)
(my-nthcdr 1 my-list)
(my-nthcdr 2 my-list)
(my-nthcdr 3 my-list)

(nth 0 my-list)
(nth 1 my-list)

(defun my-nth (n list)
  "Return nth element of LIST"
  (car (nthcdr n list)))

(my-nth 2 my-list)

;; How to use loop?
(let ((num 0))
  (while (< num 5)
    (princ (format "%d\n" num))
    (setq num (1+ num))))

(dotimes (i 5)
  (princ (format "\n%d" i)))