Accessor nth

Syntax:

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. If the length of \param{list} is not greater than \param{n}, then the result is \nil.Specifically,

 (nth n list) ≡ (car (nthcdr n list))

15.2.0 8

nth may be used to specify a place to setf. Specifically, when \funref{nth} is used in this way, \param{n} must be less than the length of the \param{list}.

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

Examples:

15.2.0 6

 (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)

Side Effects:

None.

Affected By:

None.

Exceptional Situations:

None.

See Also:

elt, first, nthcdr

Notes:

None.