See also http://hackage.haskell.org/trac/ghc/wiki/NewAxioms (as yet unimplemented)
Simon | -----Original Message----- | From: haskell-prime-boun...@haskell.org [mailto:haskell-prime- | boun...@haskell.org] On Behalf Of AntC | Sent: 24 May 2012 14:00 | To: haskell-prime@haskell.org | Subject: Re: TypeFamilies vs. FunctionalDependencies & type-level | recursion | | <oleg@...> writes: | | > | > | > I don't think Overlapping Instances will be in Haskell' any time soon | > since there are doubts about the soundness. Overlapping instances are | > clearly unsound with type functions. Whether they are sound with | > functional dependencies is not clear, but there are warning | > signs: | > | > http://www.haskell.org/pipermail/haskell-cafe/2010-July/080043.html | > | I have now worked through that post in detail, thank you. And replied | (on the cafe http://www.haskell.org/pipermail/haskell-cafe/2012- | May/101417.html ) | | As SPJ says there, I don't expect there's any real difference in the | fundeps approach compared to type families. And as a matter of taste, I | find type families more easy to understand and reason about, and more | *functional*. | | But I don't see in SPJ's post any real doubts about soundness, just | restrictions that would have to be imposed. He concludes "I believe that | if ..., then overlap of type families would be fine." | | The only onerous restriction is that overlapping instances would have to | be in a single module. And I don't think that is needed under my | proposal to dis- overlap overlaps. | | As a matter of interest, how would the TTypeable approach address those | examples? Particularly the existentials (examples 3 and 4). How would it | look inside the GADTs to discharge the constraints (or apply the type | functions)? | | I notice example 4 (and 1) 'exploits' separate compilation/imported | overlapping instances to arrive at unsoundness. How does TTypeable | handle imported instances? | | AntC | | | | _______________________________________________ | Haskell-prime mailing list | Haskell-prime@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-prime _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime