exam9.5.6

;; mht created on Nov 15, 2011

;; delta : list-of-numbers list-of-numbers -> number
;; to compute the difference of all items in t1 and t2
(define (delta t1 t2)
  (cond
    [(or
      (empty? t1) (empty? t2))
     0]
    [else (+
           (- (first t2) (first t1))
           (delta (rest t1) (rest t2)))]))


;; test
(delta empty (cons 4 (cons 5 (cons 6 empty))))
 (delta (cons 7 (cons 8 (cons 9 empty))) (cons 4 (cons 5 (cons 6 empty))))