--- a/lib/ur/list.ur	Sat Nov 20 10:45:22 2010 -0500
+++ b/lib/ur/list.ur	Sun Nov 21 15:43:24 2010 -0500
@@ -308,6 +308,20 @@
         sort' ls
     end
 
+val nth [a] =
+    let
+        fun nth (ls : list a) (n : int) : option a =
+            case ls of
+                [] => None
+              | x :: ls' =>
+                if n <= 0 then
+                    Some x
+                else
+                    nth ls' (n-1)
+    in
+        nth
+    end
+
 fun assoc [a] [b] (_ : eq a) (x : a) =
     let
         fun assoc' (ls : list (a * b)) =