On Jan 9, 2015 10:25 AM, "Ross Paterson" <R.Paterson@city.ac.uk> wrote:
> These constraints are not needed by the GHC implementations, but might be
> needed for other possible implementations, so in a sense the changes are
> leaking the GHC implementations.  This seems most clear in the Functor
> and Foldable instances for Array, and elems.  Portable implementations
> of these will require the Ix constraint -- I think it should be restored.

Agreed.

> The other cases are more arguable.  For example the change to Data.Ratio
> declares that the pair is kept in reduced form, but one could argue that
> requiring that is no bad thing.

Disagreed. However, some have argued convincingly that the Ratio type as it stands makes little sense anyway.