(define-module (prime))


(define-public (prime? n)
  "Returns #t if N is prime, else #f."

  (define (prime-helper n d)
    "Recursively checks if N is a prime number
by attempting division by number D,D-1,D-2..."
    (cond
     ((< d 2) #t)
     ((zero? (remainder n d)) #f)
     (#t (prime-helper n (1- d)))))

  (if (< n 2)
      #f
      (prime-helper n (quotient n 2))))