Functor supertype has conflicting instances

Question

I have defined a Fine-Grained Functor class (FgFunctor) in order to apply a constraint to the type of functions that may map over my Ordered Triple datatype (

Answer 1

When the compiler (GHC) looks for instances of a type class for a specific type, it doesn't take contexts of each instance into account. That's why it found two instances of FgFunctor for OrdTriple even though OrdTriple is not an instance of Functor.

GHC/AdvancedOverlap shows you how you can solve this situation.