Add sample prime factors.

.github/workflows/ci-workflow-gambit.yml

@@ -34,3 +34,6 @@ jobs:
 
     - name: Test the example
       run: gsi.exe sample\sample-unit-test.scm
+
+    - name: Test the prime factors
+      run: gsi.exe sample\prime-factors-test.scm

sample/prime-factors-test.scm

@@ -0,0 +1,23 @@
+(include "prime-factors.scm")
+(include "../assert-r5rs.scm")
+
+(test-case "one"
+    (assert-null (prime-factors 1)))
+
+(test-case "two"
+    (assert-number-list= (list 2) (prime-factors 2)))
+
+(test-case "three"
+    (assert-number-list= (list 3) (prime-factors 3)))
+
+(test-case "four"
+    (assert-number-list= (list 2 2) (prime-factors 4)))
+
+(test-case "eight"
+    (assert-number-list= (list 2 2 2) (prime-factors 8)))
+
+(test-case "nine"
+    (assert-number-list= (list 3 3) (prime-factors 9)))
+
+(test-case "max"
+    (assert-number-list= (list 2147483647) (prime-factors 2147483647)))

sample/prime-factors.scm

@@ -0,0 +1,26 @@
+(define (prime-factors n)
+    (test-candidate n 2))
+
+(define (test-candidate n candidate)
+    (cond
+        ((= n 1) (list))
+        ((too-large? n candidate) (prime n))
+        ((divides? n candidate) (keep-candidate n candidate))
+        (else (next-candidate n candidate))))
+
+(define (too-large? n candidate)
+    (> candidate (sqrt n)))
+
+(define (prime n)
+    (list n))
+
+(define (divides? n candidate)
+    (= (modulo n candidate) 0))
+
+(define (keep-candidate n candidate)
+    (append
+        (prime candidate)
+        (test-candidate (/ n candidate) candidate)))
+
+(define (next-candidate n candidate)
+    (test-candidate n (+ candidate 1)))