On Fri, May 02, 2008 at 08:30:59AM +0200, Tom Schrijvers wrote:
Note that when declaring an instance of a concrete type, like Int, the constraint (S Int) will be trivially satisfied or not at compile time. (bf2 is free to use methods of 'S' of course).
this translation is also a bijection, declaring those two instances manually as above is indistinguishable from declaring instances via the alias in all ways.
Hopefully the generalization to arbitrary numbers of classes is clear...
What about multiple parameters? Can A have more parameters than the Ci? Should they be in the same order? Should they overlap?
What about instance contexts, like:
instance I a => A a where ...
Ah, I originally had instance contexts in my example, but left them out for clarity of the main points. instance contexts are just copied verbatim into each expanded instance.
(What about functional dependencies?)
I am leaving out MPTCs and hence fundeps for now, I do not believe they will present an issue, as nothing about the expansion depends on the number of arguments, but I want to make sure we have a clear understanding of what class aliases imply for haskell 98 one constructor type classes first. I think the extension to MPTCs is clear, not so clear for fundeps but not unsolvable, then again, nothing much is clear about the future of fundeps so I don't think that is a big issue. John -- John Meacham - ⑆repetae.net⑆john⑈