Wolfgang Thaller
Proposal for Platform-Specific extensions: [...] Opinions?
Sounds like a fine plan. One little detail: what about datatype declarations? Suppose the standard version provides a datatype like this: data T = A Int | B Float and the foo backend has a third option 'C Char', I can either do: data T = A Int | B Float | C_ext Char or data T = A Int | B Float data T_ext = T_std T | C_ext Char or data T_ext = A_ext Int | B_ext Float | C_ext Char The first is more pleasant to use. The second makes the use of an extension more explicit and is less liable to result in exceptions if user code does case analysis on this type. The third seems like a reasonable compromise between the two and is probably my favourite at the moment. We'd probably want to provide helper functions with types like these: to_T_ext :: T -> T_ext from_T_ext :: T_ext -> Maybe T I'm not especially happy with any of these but I suspect they're pretty much the best that can be done within Haskell's type system. -- Alastair Reid alastair@reid-consulting-uk.ltd.uk Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/