nth n list → object

(setf (nth n list) new-object)

n — a non-negative integer.

list — a list, which might be a dotted list or a circular list.

object — an object.

new-object — an object.

nth locates the nth element of list, where the car of the list is the “zeroth” element. Specifically,

(nth n list) ≡ (car (nthcdr n list))

nth may be used to specify a place to setf. Specifically,

(setf (nth n list) new-object) ≡ (setf (car (nthcdr n list)) new-object)

(nth 0 '(foo bar baz)) → FOO 
(nth 1 '(foo bar baz)) → BAR 
(nth 3 '(foo bar baz)) → NIL 
(setq 0-to-3 (list 0 1 2 3)) → (0 1 2 3) 
(setf (nth 2 0-to-3) "two") → "two" 
0-to-3 → (0 1 "two" 3)

elt, first, nthcdr