I'm relatively new to haskell. Let's say I have a simple program like this: import Data.Map type Tree = String type StringMap = Map String String f :: StringMap -> Tree -> Tree f _ y = y ++ "!" getStringMap :: IO StringMap getStringMap = return (Data.Map.fromList [("k1","v1")]) main :: IO () main = do m <- getStringMap s <- getLine putStr $ show (f m s) ++ "\n" Ignore the implementation of f and getStringMap for now. Assume f is a fairly complex function that uses the Map during the process of transforming the Tree argument into the result Tree (here I defined Tree as a string just so that it would compile). getStringMap reads the whole Map into memory at once. However, now let's say that the whole Map is too large, so I decide to store it over a network in a remote database system instead. And then I define another function like: type Connection = String getStringMapValue :: Connection -> String -> IO String that takes a connection string and a key and returns the value. My question is this: how do I change my program to make StringMap a lazily-loaded structure based on getStringMapValue without changing f? Regards, Jeff Davis