tcfail198.hs:6:17:
    Couldn't match expected type `t0 -> t1'
                with actual type `forall a. [a] -> [a]'
    The lambda expression `\ (x : xs) -> xs ++ ...' has one argument,
    but its type `forall a. [a] -> [a]' has none
    In the first argument of `Just', namely
      `(\ (x : xs) -> xs ++ [x :: a])'
    In the expression: Just (\ (x : xs) -> xs ++ [x :: a])