nth (Accessor)

Syntax:

(setf (nth n list) new-object)

Arguments and Values:

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.

Description:

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)

Examples:

 (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)

See Also:

elt, first, nthcdr