Add net/ricketyspace/sicp/one/twentytwo.scm

1 files changed, 48 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/one/twentytwo.scm b/net/ricketyspace/sicp/one/twentytwo.scm
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+++ b/net/ricketyspace/sicp/one/twentytwo.scm
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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)
+  #:export (timed-prime-test
+            search-for-primes))
+
+(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))))