Benjamin wrote (snipped): > Typeable would be completely safe if the only way to declare instances > would be to derive them, but this is only practical if it can be done > from anywhere outside the data type definition.
Unfortunately this would also outlaw some legitimate uses of Typeable. In particular, I think you can only derive Typeable for a type constructor of type (*). GHC has recently added Typeable1,Typeable2,... which are classes of type constructors of kind *->*, *->*->* and so on, up to 6 arguments I think, and these can be derived, which is a great help. But there are still kinds this does not include; for example (*->*)->*, which is an example of a type constructor I actually used where I wanted an instance of Typeable. _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
