As an excercise, I have created a small module defining a data structure which is intended to be an efficient map from sequences (possibly very long ones) to objects of some other type. The source code is below for anyone interested. Three questions. Hopefully they aren't too naive: 1) Can anyone point me toward whatever standard modules would be most appropriate for timing this (or measuring other kinds of performance) against the naive Data.Map? 2) Any suggestions on how to improve the module itself are more than welcome. 3) In a language like this with meaningful white-space, how do people keep their lines of source code from getting too wide? There is one line below that stretched beyond the desired 80 characters and, in general, I seem to have a hard time avoiding this. Thanks for your help. -- mac -- A map from [a] to p module SequenceMap (SequenceMap, empty, insert, lookup, test) where import Prelude hiding (lookup) import qualified Data.Map import Data.Maybe data Ord a => SequenceMap a p = SequenceMap (Maybe p) (Data.Map.Map a (SequenceMap a p)) empty :: Ord a => SequenceMap a p empty = SequenceMap Nothing Data.Map.empty lookup :: Ord a => [a] -> SequenceMap a p -> Maybe p lookup [] (SequenceMap p m) = p lookup (a:as) (SequenceMap p m) = let msm = Data.Map.lookup a m in case msm of Nothing -> Nothing Just sm -> lookup as sm insert :: Ord a => [a] -> p -> SequenceMap a p -> SequenceMap a p insert [] p (SequenceMap oldP othrs) = SequenceMap (Just p) othrs insert (a:as) p (SequenceMap notP othrs) = let msm = Data.Map.lookup a othrs in case msm of Nothing -> SequenceMap notP (Data.Map.insert a (insert as p empty) Data.Map.empty) Just sm -> SequenceMap notP (Data.Map.insert a (insert as p sm) othrs) test :: Bool test = fromMaybe False (lookup "qwerty" (insert "qwerty" True empty))