Hi, Is it possible to have such a feature in the future versions of the Haskell language? For example, there is an Either datatype which is Left a| Right b. Suppose I want to extend this datatype to the one including possibility of neither Left or Right (i. e. None). Currently I have to use Maybe Either, so my options are: Just (Left a) Just (Right b) Nothing If I could extend the Either datatype I might have (syntax may be different, this is just an example) data NEither a b = <Either a b> | None where datatype in angles is a parent datatype, and all its possible data constructors are included, and their list is extended with None. which gave me possibilities: Left a | Right b | None Probably I wouldn't expect to be able to reuse Nothing here (although I might want to) because Nothing already has been defined to be of the type Maybe. This is just a suggestion, that's why it is posted in the Cafe. PS Or is there a similar feature in the language already? Regarding reusing constructor names across several datatypes: is it possible to qualify them with their enclosing datatype name, like Maybe.Nothing where there is a name conflict? Then I might reuse Nothing in my hypothetical data type, and it would be NEither.Nothing if conflicting with Maybe.Nothing PPS I may be missing something again, as always ;) -- Dimitry Golubovsky Anywhere on the Web