gistfile1.rkt

;;function lis-length returns the length of a list
;;list -> number
(define (lis-length lis)
  (cond [(empty? lis) 0]
        [else (add1 (lis-length (rest lis)))]))

(check-expect (lis-length (list 1 2 3 4 5)) 5)
(check-expect (lis-length empty) 0)
(check-expect (lis-length (list 1)) 1)

;;function mean computes the mean of a list of numbers
;;list-of-numbers -> number

(define (mean lis)
  (cond [(empty? (rest lis)) (first lis)]
        [else (/ (+ (* (mean (rest lis)) 
                       (lis-length (rest lis))) 
                    (first lis)) 
                 (lis-length lis))]))

(check-expect (mean (list 0 2))
              1)

(check-expect (mean (list 10 10 10 10 0))
              8)

(check-expect (mean (list 8))
              8)