[Haskell-cafe] Re: Decoupling type classes (e.g. Applicative)?

[Maciej Piechotka]

On Tue, 2010-11-02 at 21:57 -0400, Brandon S Allbery KF8NH wrote:
> On 10/29/10 09:35 , Dominique Devriese wrote:
> > * Only introduce a dependency from type class A to type class B if all
> >   functions in type class B can be implemented in terms of the
> >   functions in type class A or if type class A is empty.
> 
> Er?  Eq a => Ord a makes perfect sense in context but violates this law.


x == y = case x `compare` y of EQ -> True; _ -> False

Or using (==) inside definition:

(==) = ((== EQ) .) . compare

Class A - Ord, B - Eq.

Regards
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