On 15.08.2011 14:36, Simon Peyton-Jones wrote:
I don't completely understant how does it work. Does client need to enable language extension to get default instances?With help from Conor we have made some progress on this: we have a draft design: http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstancesIf you care about the issue, maybe you can help resolve the above questions. In particular, to give concrete evidence for (b), working out some case studies would be a Good Thing. The examples given in other proposals using the extension proposed here would be one starting point.
Also proposal cannot fix Functor/Applicative/Monad problem without breaking client code. It requires explicit opt-out but client may define Applicative instance. And unless "hiding" is added it will result in compile error.
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