Proposal: Remove Show and Eq superclasses of Num

[Paterson, Ross]

Ian Lynagh writes:
> I would like to propose that we remove the Show and Eq superclasses from
> Num, i.e. change
>     class  (Eq a, Show a) => Num a  where
>         [...]
> to
>     class  Num a  where
>         [...]

This will break client code, but will not fix other defects of Num,
namely the inclusion of abs/signum, and tying (*) to (+).  I think the
right approach is to refactor the numeric classes along algebraic lines:

http://hackage.haskell.org/package/yap

Leave Num with its broken interface for backward compatibility (for
clients), but provide a clean Ring superclass for new code.