prime.scm

(define (square x) (* x x))

(define (smallest-divisor n)
  (define (find-divisor n test-divisor)
    (cond ((> (square test-divisor) n)
	   n)
	  ((divides? test-divisor n)
	   test-divisor)
	  (else (find-divisor n (+ test-divisor 1)))))

  (define (divides? a b)
    (= (remainder b a) 0))
  (find-divisor n 2))

(define (prime? n)
  (= n (smallest-divisor n)))

(define (timed-prime-test n)
  (newline)
  (display n)
  (start-prime-test n (runtime)))

(define (start-prime-test n start-time)
  (if (prime? n)
    (report-prime (- (runtime) start-time))))

(define (report-prime elapsed-time)
  (display " *** ")
  (display elapsed-time))

(define (search-for-primes start end)
  (if (even? start)
    (search-for-primes (+ start 1) end)
    (cond ((< start end) (timed-prime-test start)
			 (search-for-primes (+ start 2) end)))))