;; (check-star) consumes a Str S and returns "****" if it is a 4-lettered string
;;    else returns the same string
;; check-star : Str -> Str

(define (check-star S)
  (cond
    [(equal? (string-length S) 4) "****"]
    [else S]))

;; (censor L) consumes a (listof Str) L and returns a Str with all list members
;;    combined to form a single sentence and every 4-letter member
;;    changed to "****"
;; censor : (listof Str) -> Str

(define (censor L)
  (join (map check-star L)))