I am using the haskell extensions (in Hugs - Nov 2002) and I have some troubles with that. For example:
class A a where a :: a -> String a = const "a"
class B b where b :: b -> String b = const "b"
instance (A b) => B b where b = a
instance B ()
----------------- In this case, Hugs says:
ERROR "Test.hs":12 - Overlapping instances for class "B" *** This instance : B () *** Overlaps with : B a *** Common instance : B ()
but I don't have an instance "A ()" from which haskell can infer an instance "B ()".
can somebody explain me that it is happening here?
Thanks in advanced...
Diego
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