Superclass equalities

Simon Peyton-Jones simonpj at
Wed Jun 22 18:57:28 CEST 2011


I have long advertised a plan to allow so-called superclass equalities.  I've just pushed patches to implement them. So now you can write

	class (F a ~ b) => C a b where  { ... }

This email is just to encourage you to try them out.  

Currently this is just in the HEAD git repository.  It'll appear in GHC 7.2, a release we are now actively preparing.  But the feature isn't heavily tested (since it didn't exist until today), so I'd appreciate people trying it out.



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