Error found:
in module FunctorInstance1
at tests/purs/failing/FunctorInstance1.purs:8:1 - 8:29 (line 8, column 1 - line 8, column 29)

  One or more type variables are in positions that prevent Functor from being derived.
  To derive this class, make sure that these variables are only used as the final arguments to type constructors, that their variance matches the variance of Functor, and that those type constructors themselves have instances of Data.Functor.Functor, Data.Bifunctor.Bifunctor, Data.Functor.Contravariant.Contravariant, or Data.Profunctor.Profunctor.

  tests/purs/failing/FunctorInstance1.purs:
      6 
      7 data Test a = Test (Predicate a)
      8 derive instance Functor Test


See https://github.com/purescript/documentation/blob/master/errors/CannotDeriveInvalidConstructorArg.md for more information,
or to contribute content related to this error.