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;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
(define-module (net ricketyspace sicp one twentytwo)
#:use-module (net ricketyspace sicp utils)
#:use-module (srfi srfi-1)
#:export (timed-prime-test
search-for-primes
three-primes-gt
three-primes-gt-1000
three-primes-gt-10000
three-primes-gt-100000
three-primes-gt-1000000))
(define (square x)
(expt x 2))
(define (divides? a b)
(= (remainder b a) 0))
(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 (smallest-divisor n)
(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))
#f))
(define (report-prime elapsed-time)
(display " *** ")
(display elapsed-time) #t)
(define (odd-and-prime n)
(and (odd? n) (timed-prime-test n)))
(define (search-for-primes start end)
(cond ((> start end) '())
((odd-and-prime start)
(cons start (search-for-primes (1+ start) end)))
(else (search-for-primes (1+ start) end))))
(define (three-primes-gt n)
(three-primes-gt-iter n 10 '()))
(define (three-primes-gt-iter n e l)
(cond ((> (length l) 3) (take l 3))
(else (three-primes-gt-iter n
(+ e 10)
(search-for-primes n e)))))
(define (three-primes-gt-1000)
(three-primes-gt 1000))
(define (three-primes-gt-10000)
(three-primes-gt 10000))
(define (three-primes-gt-100000)
(three-primes-gt 100000))
(define (three-primes-gt-1000000)
(three-primes-gt 1000000))
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