T12055a.hs:28:1: error: [GHC-80003]
    • Non type-variable argument in the constraint: Category (Dom f)
    • In the context: (Category (Dom f), Category (Cod f))
      While checking the super-classes of class ‘Functor’
      In the class declaration for ‘Functor’
    Suggested fix: Perhaps you intended to use FlexibleContexts