Added hw 9

Homework_9/tree.hs

@@ -0,0 +1,31 @@
+import Prelude hiding (lookup)
+
+data BinaryTree k v = None | Node {
+	  key    :: k
+	, value  :: v
+	, left   :: BinaryTree k v
+	, right  :: BinaryTree k v
+}
+
+lookup :: Ord k => k -> BinaryTree k v -> Maybe v
+lookup k None = Nothing
+lookup k n |(key n) == k = Just (value n)
+		   |(key n) > k = lookup k (left n)
+		   |otherwise = lookup k (right n)
+
+insert :: Ord k => k -> v -> BinaryTree k v -> BinaryTree k v
+insert k v None = Node k v None None
+insert k v n | (key n) == k = Node k v (left n) (right n)
+			 | (key n) > k = Node (key n) (value n) (insert k v (left n)) (right n)
+			 | otherwise = Node (key n) (value n) (left n) (insert k v (right n))
+
+merge :: Ord k => BinaryTree k v -> BinaryTree k v -> BinaryTree k v
+merge a None = a
+merge None b = b
+merge a b = Node (key a) (value a) (left a) (merge (right a) b)
+
+delete :: Ord k => k -> BinaryTree k v -> BinaryTree k v
+delete k None = None
+delete k n | (key n) == k = merge (left n) (right n)
+		   | (key n) > k = Node (key n) (value n) (delete k (left n)) (right n)
+		   | otherwise = Node (key n) (value n) (left n) (delete k (right n))