hello i'm new to haskell so i'm sorry if this is a stupid question, but i'm having problems with some basic code. the code : data Maybe Dir = Just Dir | Nothing data Dir = Left | Right | Up | Down data Piece = Vertical | Horizontal | CodeA | CodeB flow = [(Horizontal, Left, Left), (Horizontal, Right, Right), (Vertical, Down, Down), (Vertical, Up, Up), ................ etc ] fst :: (a,b,c) -> a fst (x,y,z) = x scnd :: (a,b,c) -> b scnd (x,y,z) = y third :: (a,b,c) -> c third (x,y,z) = z element :: [(Piece, Dir, Dir)] -> Maybe Dir element [] = Nothing element xs = Just (third (head xs)) chgDir :: Piece -> Dir -> Maybe Dir chgDir p d = element (filter (\x -> p == (fst x)) (filter (\x -> d == (scnd x)) flow)) the error i get : Instances of (Eq Dir, Eq Piece) required for definition of chgDir i don't know what's happening. help!!! thanks in advance