1-22.scm

;calculate prime
(define (smallest-divisor n)
  (find-divisor n 2))
(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))
(define (prime? n)
  (= n (smallest-divisor n)))

;timing
(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))
      "nothing"))
(define (report-time elapsed-time)
  (display " *** ")
  (display elapsed-time))

(define (search-for-primes start-range end-range)
  (if (even? start-range)
      (search-for-primes (+ 1 start-range) end-range)
      (cond ((> start-range end-range)
             (newline) (display "done"))
            (else (timed-prime-test start-range)
                  (search-for-primes (+ 2 start-range) end-range)))))