(setf (svref simple-vector index) new-element)
index - a valid array index for the simple-vector.
element, new-element - an object (whose type is a subtype of the array element type of the simple-vector).
(simple-vector-p (setq v (vector 1 2 'sirens))) true (svref v 0) 1 (svref v 2) SIRENS (setf (svref v 1) 'newcomer) NEWCOMER v #(1 NEWCOMER SIRENS)
(svref v i) ==(aref (the simple-vector v) i)