T1900.hs:7:3: error:
    • Couldn't match type ‘Depend s0’ with ‘Depend s’
      NB: ‘Depend’ is a type function, and may not be injective
      The type variable ‘s0’ is ambiguous
      Expected type: Depend s -> Depend s
        Actual type: Depend s0 -> Depend s0
    • In the ambiguity check for ‘trans’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the class method:
        trans :: forall s. Bug s => Depend s -> Depend s
      In the class declaration for ‘Bug’