Hi, I'm experimenting with Haskell typeclasses and could do with some advice on managing superclasses and instance declarations. Suppose I have these modules (please ignore any misunderstandings of abstract algebra concepts): -- in Semigroup.hs class Semigroup a where (|.|) :: a -> a -> a instance Semigroup Integer where (|.|) = (+) -- In Monoid.hs class (Semigroup a) => Monoid a where identity :: a instance Monoid Integer where identity = 0 -- In Group.hs class (Monoid a) => Group a where inverse :: a -> a instance Group Integer where (|.|) = (+) identity = 0 inverse = (-) In Group.hs I'm trying to create an (additive) group instance for Integer values but GHC complains that (|.|) and identity are not "visible" typeclass methods. I understand that if I explicitly recreate Semigroup and Monoid instances for Integer in Group.hs it will fix the visibility issue--at the cost of duplicating the instances already defined in Semigroup.hs and Monoid.hs. I'm starting to wonder whether it's a good idea to create typeclass instances in the same modules as the typeclass definitions? In my case I could create a separate Instances.hs with the instance declarations but how do Haskellers generally handle this situation? Thanks, Stu