Shorten shuffle and improve its randomness (previous one declusters poorly)

KoiKoi.hs

@@ -62,13 +62,8 @@ shuffle l =
   aux (length l) l
   where
     aux n [] = return []
-    aux n [a] = return [a]
-    aux n l = do
-      cut <- randomRIO (0, n - 1)
-      let (top, bottom) = splitAt cut l
-      shuffledTop <- aux cut top
-      shuffledBottom <- aux (n - cut) bottom
-      reorder <- randomRIO (False, True)
-      return $ if reorder
-        then shuffledTop ++ shuffledBottom
-        else shuffledBottom ++ shuffledTop
+    aux n (h:t) = do
+      cut <- randomRIO (0, n-1)
+      shuffled <- shuffle t
+      let (top, bottom) = splitAt cut shuffled
+      return $ top ++ h : bottom