Hi, I've run into a small problem whilst doing some manual type checking, to see if I could match the results given by hugs prelude> :t foldr filter foldr filter :: [a] -> [a -> Bool] -> [a] -- This was fine and was the same as my answer, so I tested it with prelude> foldr filter [1,2,3,4] [even,odd] -- and the answer was indeed an empty list -- However I got stuck when attempting to derive the result of map (foldr filter) -- Hugs says that: prelude> :t map (foldr filter) map (foldr filter) :: [[a]] -> [[a -> Bool] -> [a]] Two main questions: 1/ How does hugs derive this answer? 2/ What input can I give so that it yields a correct result? I've tried giving it a list of lists but it fails... Any pointers would be greatly appreciated! Many Thanks, Lee _________________________________________________________________ Stay in touch with absent friends - get MSN Messenger http://www.msn.co.uk/messenger