VECTOR-PUSH-EXTEND function pushes new-element into specified vector. Supplied vector must be adjustable (see MAKE-ARRAY) and have fill-pointer. New element is placed at last fill-pointer position and fill-pointer is incremented. Vector size is adjusted a number of items as specified by extension argument, if necessary. See also MAKE-ARRAY, VECTOR-POP and VECTOR-PUSH. Return value is index at which the new item was placed.

(defparameter *v* (make-array 2 :fill-pointer 0 :adjustable t)) => *V*
(vector-push-extend 4 *v*) => 0
(vector-push-extend 3 *v*) => 1
(vector-push-extend 2 *v*) => 2
*v* => #(4 3 2)
(vector-pop *v*) => 2
(vector-pop *v*) => 3
(vector-pop *v*) => 4