/
ex1.22.scm
33 lines (32 loc) · 943 Bytes
/
ex1.22.scm
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(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)) false))
(define (report-prime elapsed-time)
(display " *** ")
(display elapsed-time)
true)
(define (prime? n)
(= (smallest-divisor n) 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? test-divisor n)
(= (remainder n test-divisor) 0))
(define (search-for-primes n)
(define (even? n)
(= (remainder n 2) 0))
(define (iter n counter)
(if (< counter 3)
(if (timed-prime-test n)
(iter (+ n 2) (+ counter 1))
(iter (+ n 2) counter))))
(if (even? n)
(iter (+ n 1) 0)
(iter (+ n 2) 0)))