How do I run z "a" from ghci or the IO monad? module Foo where import qualified Data.Map as M import Control.Monad import Control.Monad.List import Prelude hiding ((!!)) (!!) :: (Ord k, MonadPlus m) => [M.Map k v] -> k -> m v (!!) maps key = msum $ map (M.lookup key) maps x :: M.Map String Int = M.empty y :: M.Map String Int = M.fromList [("a", 1)] z m = [x, y] !! m Thanks, Joel -- http://wagerlabs.com/