data Tuple a b c d = SingleTuple a
                   | DoubleTuple a b
                   | TripleTuple a b c
                   | QuadrupleTuple a b c d 

tuple1 :: Tuple a b c d -> Maybe a
tuple1 (SingleTuple a) = Just a
tuple1 (DoubleTuple a b) = Just a
tuple1 (TripleTuple a b c) = Just a
tuple1 (QuadrupleTuple a b c d) = Just a

tuple2 :: Tuple a b c d -> Maybe b
tuple2 (SingleTuple a) = Nothing
tuple2 (DoubleTuple a b) = Just b
tuple2 (TripleTuple a b c) = Just b
tuple2 (QuadrupleTuple a b c d) = Just b

tuple3 :: Tuple a b c d -> Maybe c
tuple3 (SingleTuple a) = Nothing
tuple3 (DoubleTuple a b) = Nothing
tuple3 (TripleTuple a b c) = Just c
tuple3 (QuadrupleTuple a b c d) = Just c

tuple4 :: Tuple a b c d -> Maybe d
tuple4 (SingleTuple a) = Nothing
tuple4 (DoubleTuple a b) = Nothing
tuple4 (TripleTuple a b c) = Nothing 
tuple4 (QuadrupleTuple a b c d) = Just d