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Simon Peyton Jones authored
This patch does some signficant refactoring to the treatment of default methods in class declarations, and more generally to the type checking of type/class decls. Highlights: * When the class has a generic-default method, such as class C a where op :: a -> a -> Bool default op :: Ord a => a -> a -> a the ClassOpItem records the type of the generic-default, in this case the type (Ord a => a -> a -> a) * I killed off Class.DefMeth in favour of the very-similar BasicTypes.DefMethSpec. However it turned out to be better to use a Maybe, thus Maybe (DefMethSpec Type) with Nothing meaning "no default method". * In TcTyClsDecls.tcTyClGroup, we used to accumulate a [TyThing], but I found a way to make it much simpler, accumulating only a [TyCon]. Much less wrapping and unwrapping. * On the way I also fixed Trac #10896 in a better way. Instead of killing off all ambiguity checks whenever there are any type errors (the fix in commit 8e8b9ed9), I instead recover in TcTyClsDecls.checkValidTyCl. There was a lot of associated simplification all round
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