#lang typed/racket

(define sample "0-306-40615-2")
(define sample2 "978-0-306-40615-7")

(: bind-values (-> String (Listof Integer)))
(define (bind-values x)
  (cast (filter complex?
                (map (lambda ([s : String])
                       (if (string=? s "X")
                           10
                           (string->number s)))
                     (regexp-match* #rx"." x)))
        (Listof Integer)))

(: isbn10? (-> String Boolean))
(define (isbn10? x)
  (let ([z (foldl + 0 (map * (bind-values x) (range 1 11)))])
    (cond
      [(zero? (modulo z 11)) true]
      [else false])))

(: isbn13? (-> String Boolean))
(define (isbn13? x)
  (let ([z (foldl + 0 (for/list: : (Listof Integer)
                                 ([i (in-naturals)]
                                  [j (bind-values x)])
                        (if (even? i)
                            j
                            (* 3 j))))])
    (cond
      [(zero? (modulo z 10)) true]
      [else false])))

(: isbn? (-> String Boolean))
(define (isbn? x)
  (let ([z : String (regexp-replace* #px"[^\\dX]" x "")])
    (match (string-length z)
      [10 (isbn10? z)]
      [13 (isbn13? z)]
      [_ false])))

(isbn? sample)