Glue modules.

src/GF/Data/RedBlack.hs

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+{- 
+   **************************************************************
+   * Filename      : RedBlack.hs                                *
+   * Author        : Markus Forsberg                            *
+   *                 markus@cs.chalmers.se                      *
+   * Last Modified : 15 December, 2001                          *
+   * Lines         : 57                                         *
+   ************************************************************** 
+-} -- Modified version of Osanaki's implementation.
+
+module RedBlack (
+                emptyTree,
+		Tree,
+		lookupTree,
+		insertTree,
+		flatten
+		) where
+
+data Color = R | B
+ deriving (Show,Read)
+
+data Tree key el = E | T Color (Tree key el) (key,el) (Tree key el)
+ deriving (Show,Read)
+
+balance :: Color -> Tree a b -> (a,b) -> Tree a b -> Tree a b  
+balance B (T R (T R a x b) y c) z d = T R (T B a x b) y (T B c z d)
+balance B (T R a x (T R b y c)) z d = T R (T B a x b) y (T B c z d)
+balance B a x (T R (T R b y c) z d) = T R (T B a x b) y (T B c z d)
+balance B a x (T R b y (T R c z d)) = T R (T B a x b) y (T B c z d)
+balance color a x b = T color a x b
+
+emptyTree :: Tree key el
+emptyTree = E
+
+lookupTree :: Ord a => a -> Tree a b -> Maybe b
+lookupTree _ E = Nothing
+lookupTree x (T _ a (y,z) b)
+   | x < y      = lookupTree x a
+   | x > y      = lookupTree x b
+   | otherwise  = return z
+   
+insertTree :: Ord a => (a,b) -> Tree a b -> Tree a b
+insertTree (key,el) tree = T B a y b
+  where 
+    T _ a y b = ins tree
+    ins E = T R E (key,el) E
+    ins (T color a y@(key',el') b)
+      | key < key'    = balance color (ins a) y b
+      | key > key'    = balance color a y (ins b)
+      | otherwise     = T color a (key',el) b
+
+flatten :: Tree a b -> [(a,b)]
+flatten E = []
+flatten (T _ left (key,e) right) 
+  = (flatten left) ++ ((key,e):(flatten right))