On Thu, Jul 10, 2003 at 02:33:25PM +0100, Ross Paterson wrote: > Subclasses in Haskell cover a range of relationships, including this > sense where things in the subclass automatically belong to the superclass. > Other examples include Eq => Ord and Functor vs Monad. In such cases it > would be handy if the subclass could define defaults for the superclass > methods (e.g. Ord defining (==)), so that the superclass instance could > be optional.
I agree, but this needs to be carefully thought out. For instance,
remember to consider the case that there is more than one default
instance for a given method of a superclass. I am reminded of
multiple inheritance considerations.
(These difficulties came up before when I was thinking about the
numeric heirarchy, and was the reason I proposed a heirarchy which was
much less fine-grained than, e.g., in Mechvelliani's proposal.)
Peace,
Dylan
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