;; IN: a vector, an index, a new value
;; SideEffect: inserts new value at the input index in the vector, pushes everything back, discards last element


(define (vector-shift! vec index)
  (define (loop n)
    (if (= n index) 'okay
	(begin
	(vector-set! vec n
		     (vector-ref vec (- n 1)))
	(loop (- n 1)))))
  (loop (- (vector-length vec) 1)))


(define (vector-insert! vec index val)
  (vector-shift! vec index)
  (vector-set! vec index val))