Add prime? code and tests

1 files changed, 17 insertions, 0 deletions

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)))))