gistfile1.hs

import Control.Monad

-- HashGraph                                                                                                                                                                                                                     

class HashGraph digest value m where
  hash :: value -> m digest
  unhash :: digest -> m value

instance (Monad m) => HashGraph a a m where
  hash = return
  unhash = return


-- RedBlack Tree Balancing                                                                                                                                                                                                       

data Color = R | B deriving Show
data Tree k d = E | T Color d k d deriving Show

insert :: (Ord k, Monad m,
           HashGraph d (Tree k (m d)) m) =>
           k -> (Tree k (m d)) -> m d
insert k E = hash $ T B (return E) k (return E)