(define make-verifier
  (lambda (f m)
    (define add-up
      (lambda (n addend position)
        (if (= n 0)
            addend
            (add-up (quotient n 10)
                    (+ addend 
                       (f position (remainder n 10)))
                    (+ position 1)))))
    (lambda (number-to-check)
      (divides? m (add-up number-to-check 0 1)))))

(define divides?
  (lambda (d n)
    (= (remainder n d) 0)))

(define isbn-ok? (make-verifier * 11))

(define upc-ok? (make-verifier (lambda (i di)
                                 (cond ((even? i)
                                        (* 3 di))
                                       ((odd? i)
                                        di)))
                               10))