Hello Brian, Friday, August 18, 2006, 8:54:08 PM, you wrote:
classes: lack of record extension mechanisms (such at that implemented in O'Haskell) and therefore inability to reuse operation implementation in an derived data type...
You can reuse ops in a derived data type but it involves a tremendous amount of boilerplate. Essentially, you just use the type classes to simulate extendable records by having a method in each class that accesses the fixed-length record corresponding to that particular C++ class.
btw, i just found the following in HWN: * HList updates . Oleg Kiselyov [17]announced that HList, the library for strongly typed heterogeneous lists, records, type-indexed products (TIP) and co-products is now accessible via darcs, [18]here. Additionally, Oleg pointed to some new features for HList, including a new representation for open records. Finally, he [19]published a note on how HList supports, natively, polymorphic variants: extensible recursive open sum datatypes, quite similar to Polymorphic variants of OCaml. HList thus solves the `expression problem' -- the ability to add new variants to a datatype without changing the existing code. 17. http://article.gmane.org/gmane.comp.lang.haskell.general/13905 18. http://darcs.haskell.org/HList/ 19. http://article.gmane.org/gmane.comp.lang.haskell.general/13906 -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com