Cleanup prime?

2 files changed, 52 insertions, 0 deletions

diff --git a/prime?/prime-test.scm b/prime?/prime-test.scm
new file mode 100644
index 0000000..3add85a
--- /dev/null
+++ b/prime?/prime-test.scm
@@ -0,0 +1,35 @@
+;; -*- compile-command: "guile -L . prime-test.scm"; -*-
+(use-modules (srfi srfi-64)
+             (prime))
+
+(test-begin "harness")
+
+
+(test-assert "test-not-prime-0"
+  (not (prime? 12)))
+
+(test-assert "test-not-prime-1"
+  (not (prime? 21)))
+
+(test-assert "test-prime"
+  (prime? 13))
+
+(test-assert "test-prime-large"
+  (prime? 1000033))
+
+(test-assert "test-two"
+  (prime? 2))
+
+;; one is NOT considered prime!
+(test-assert "test-one"
+  (not (prime? 1)))
+
+;; zero is NOT considered prime!
+(test-assert "test-zero"
+  (not (prime? 0)))
+
+(test-assert "test-negative"
+  (not (prime? -13)))
+
+
+(test-end "harness")
diff --git a/prime?/prime.scm b/prime?/prime.scm
new file mode 100755
index 0000000..3d08a35
--- /dev/null
+++ b/prime?/prime.scm
@@ -0,0 +1,17 @@
+(define-module (prime))
+
+
+(define-public (prime? n)
+  "Returns #t if N is prime, else #f."
+
+  (define (prime-helper n d)
+    "Recursively checks if N is a prime number
+by attempting division by number D,D-1,D-2..."
+    (cond
+     ((< d 2) #t)
+     ((zero? (remainder n d)) #f)
+     (#t (prime-helper n (1- d)))))
+
+  (if (< n 2)
+      #f
+      (prime-helper n (quotient n 2))))