Trie 1

gistfile1.hs

import Data.Map (Map)
import qualified Data.Map as M
import Data.Maybe

data Trie k v = Trie (Maybe v) (Map k (Trie k v)) deriving Show

empty :: Trie k v
empty = Trie Nothing M.empty

look :: Ord k => [k] -> Trie k v -> Maybe v
look [] (Trie b _) = b
look (k:ks) (Trie _ m) = M.lookup k m >>= look ks

bind :: Ord k => [k] -> v -> Trie k v -> Trie k v
bind [] x (Trie _ m) = Trie (Just x) m
bind (k:ks) x (Trie b m) = Trie b (M.insert k t' m)
  where
    t = fromMaybe empty $ M.lookup k m
    t' = bind ks x t