(use srfi-19)
(define (timed-prime-test n)
(define (start-prime-test n start-time)
(if (prime? n)
(report-prime start-time)))
(define (report-prime start-time)
(display " *** ")
(display (time-difference (current-time) start-time)))
(define (prime? n)
(= n (smallest-divisor n)))
(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)
(= (modulo b a) 0))
(define (square n)
(* n n))
(display n)
(start-prime-test n (current-time)))
(timed-prime-test 90000000019)
(timed-prime-test 90000000020)
(timed-prime-test 300000000077)
(timed-prime-test 300000000078)