Re: default roles

Hi, Am Mittwoch, den 09.10.2013, 23:18 -0400 schrieb Richard Eisenberg:

On Oct 9, 2013, at 6:24 PM, Joachim Breitner wrote:

...

So the conclusion is indeed: Let type class constraints have a nominal role, and all is fine.

But, then it would seem that any class with a superclass wouldn't be compatible with GND. Do you see that detail as a consequence of this design?

I think this approach might work, but I'm not yet convinced.

given that we coerce the fields individually already, and are not going to change that, I don’t think there is a problem with superclasses. Even more so: The instance datatype of the subclass will have a field that contains the instance _datatype_ of the superclass, not a field with a type class constraint (because as soon as we talk about dictionaries, we are in Core, where the instance _type functions_ have already been resolved), which would be representational. It probably is confusing that (IIRC) the same TyCon is used for both uses of classes: At the Haskell level, as a function on types; at the core level, as a regular datatype. Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0x4743206C Debian Developer: nomeata@debian.org