;; An LOS (list of strings) is one of: 
;; - empty
;; - (cons String LOS)

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

;; Examples
(check-expect (sum-lengths empty) 0)
(check-expect (sum-lengths (cons "hi" empty)) 2)
(check-expect (sum-lengths (cons "world" (cons "hi" empty))) 7)
(check-expect (sum-lengths (cons "northeastern" (cons "hi" empty))) 14)

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

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


(check-expect (in? empty "Ben") false) 
(check-expect (in? (cons "hi" empty) "hi") true)
(check-expect (in? (cons "hi" empty) "hello") false)
(check-expect (in? (cons "world" (cons "hi" empty)) "worl") false)