nth

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ANSI Common Lisp 14 Conses 14.2 Dictionary of Conses

14.2.22 nth Accessor

Syntax:

nth n list object

(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

Allegro CL Implementation Details:

None.

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