2 files changed, 59 insertions, 0 deletions
diff --git a/prime/prime-test.scm b/prime/prime-test.scm
new file mode 100644
index 0000000..a1c7562
--- /dev/null
+++ b/prime/prime-test.scm
@@ -0,0 +1,42 @@
+(use-modules (srfi srfi-64)
+             (prime))
+
+(test-begin "harness")
+
+
+(test-equal "test-not-prime-0"
+  #f
+  (prime? 12))
+
+(test-equal "test-not-prime-1"
+  #f
+  (prime? 21))
+
+(test-equal "test-prime"
+  #t
+  (prime? 13))
+
+(test-equal "test-prime-large"
+  #t
+  (prime? 1000033))
+
+(test-equal "test-two"
+  #t
+  (prime? 2))
+
+;; one is NOT considered prime!
+(test-equal "test-one"
+  #f
+  (prime? 1))
+
+;; zero is NOT considered prime!
+(test-equal "test-zero"
+  #f
+  (prime? 0))
+
+(test-equal "test-negative"
+  #f
+  (prime? -13))
+
+
+(test-end "harness")
diff --git a/prime/prime.scm b/prime/prime.scm
new file mode 100755
index 0000000..e12dfb4
--- /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."
+  (if (< n 2)
+      #f
+      (prime-helper n (quotient n 2))))
+
+(define (prime-helper n d)
+  "Recursively checks if N is a prime number
+by attempting division by number D,D-1,D-2..."
+  (if (< d 2)
+      #t
+      (if (equal? (remainder n d) 0)
+          #f
+          (prime-helper n (- d 1)))))