SumBag: Add some internal documentation

src/Data/SumBag.hs

@@ -57,7 +57,7 @@ instance Foldable SumBag where
 
   toList = toAscList
   {-# INLINE toList #-}
-  
+
 
 data MetaData a = MetaData
   { nodeSize :: Int
@@ -160,7 +160,7 @@ fromList = foldr insert empty
 
 -- Internal functions
 
--- | "Smart" constructor for Node. Will compute the meta data from its subtrees
+-- | "Smart" constructor for Node, will compute the meta data from its subtrees.
 node :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 node a left right =
   let nodeData = MetaData
@@ -169,23 +169,48 @@ node a left right =
         }
   in Node nodeData a left right
 
+--   a              b
+--  / \            / \
+-- x   b     =>   a   z
+--    / \        / \
+--   y   z      x   y
 rotateSingleLeft :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 rotateSingleLeft a x (Node _ b y z) = node b (node a x y) z
 rotateSingleLeft _ _ _ = error "rotateSingleLeft called with empty right tree"
 
+--     b           a
+--    / \         / \
+--   a   z   =>  x   b
+--  / \             / \
+-- x   y           y   z
 rotateSingleRight :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 rotateSingleRight b (Node _ a x y) z = node a x (node b y z)
 rotateSingleRight _ _ _ = error "rotateSingleRight called with empty left tree"
 
+--    a                  b
+--  /   \              /   \
+-- x     c           a       c
+--      / \    =>   / \     / \
+--     b   z       x  y1   y2  z
+--    / \
+--   y1 y2
 rotateDoubleLeft :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 rotateDoubleLeft a x (Node _ c (Node _ b y1 y2) z) = node b (node a x y1) (node c y2 z)
 rotateDoubleLeft _ _ _ = error "rotateDoubleLeft called with too small right tree"
 
+--      c                 b
+--    /   \             /   \
+--   a     z          a       c
+--  / \        =>    / \     / \
+-- x   b            x  y1   y2  z
+--    / \
+--  y1   y2
 rotateDoubleRight :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 rotateDoubleRight c (Node _ a x (Node _ b y1 y2)) z = node b (node a x y1) (node c y2 z)
 rotateDoubleRight _ _ _ = error "rotateDoubleRight called with too small left tree"
 
 
+-- | Performs a single balancing act on a node.
 balance1 :: Monoid a => Element a -> SumBag a -> SumBag a -> SumBag a
 balance1 a left right
   -- Subtrees have only one element