;; A Grocery-List is one of
;;  - empty
;;  - (cons Symbol Grocery-List)

;; Grocery-List examples
(define gl1 empty)
(define gl2 (cons 'eggs (cons 'beer (cons 'bread empty))))
(define gl3 (cons 'milk empty))

;; count-items : Grocery-List -> Number
;; counts how many items are on a grocery list

#| Template
(define (count-items gl)
  (cond
    [(empty? gl) ... ]
    [(cons? gl) ... (first gl) ...
                ... (count-items (rest gl)) ... ]))
|#

(define (count-items gl)
  (cond
    [(empty? gl) 0]
    [(cons? gl) (+ 1 (count-items (rest gl)))]))

;; Examples/tests
(= (count-items gl1) 0)
(= (count-items gl2) 3)
(= (count-items gl3) 1)