;; A LOS (List of Strings) is one of: 
;; - empty
;; - (cons String LOS)

;; LOS -> ?
#;(define (los-temp an-los)
  (cond [(empty? an-los) ...]
        [(cons? an-los) ... (first an-los) 
                        ... (los-temp (rest an-los))... ]))

;; count : LOS -> Number
;; count the number of strings in given list
(define (count los)
  (cond [(empty? los) 0]
        [(cons? los) (+ 1 (count (rest los)))]))

(define los1 empty)
(define los2 (cons "Jacob" empty))
(define los3 (cons "Sean" los2))

(check-expect (count los1) 0)
(check-expect (count los2) 1)
(check-expect (count los3) 2)

;; total-len : LOS -> Number
;; sum up lengths of all strings in list
(define (total-len los)
  (cond [(empty? los) 0]
        [(cons? los) (+ (string-length (first los))
                        (total-len (rest los)))]))

(check-expect (total-len los1) 0)
(check-expect (total-len los2) 5)
(check-expect (total-len los3) 9)

;; in? : LOS String -> Boolean
;; Is the string s in the list los?
(define (in? los s)
  (cond [(empty? los) false]
        [(cons? los) (or (string=? (first los) s)
                        (in? (rest los) s))]))


(check-expect (in? los1 "Sean") false)
(check-expect (in? los2 "Sean") false)
(check-expect (in? los3 "Sean") true)