[Haskell-cafe] Ensuring all values of an ADT are explicitly handled OR finding all occurrences of type X in my app

Hi, If I have the following ADT data BookingState = Confirmed | Cancelled which had a very high chance of being expanded in the future to have more values. How do I ensure that every pattern match on BookingState matches each value explicitly. Basically prevent the '_' matcher ? If that is not possible, is the following possible instead: evolve BookingState and then find all possible occurrences of values of BookingState throughout my app? I'm basically trying to make sure that any a newly added state, which may require special-case handling is not automatically handled by the '_' branch. -- Saurabh.