EitherT[Option, ?, ?]] can't be used as a bifunctor #4569
Description
With scala 2.13.12
and cats-core 2.10.0
type MyBifunctor[A, B] = EitherT[Option, A, B]
val myByFunctor = implicitly[Bifunctor[MyBifunctor]]
Does not compile :
ambiguous implicit values:
both method catsDataBitraverseForEitherT in class EitherTInstances1 of type [F[_]](implicit F: cats.Traverse[F]): cats.Bitraverse[[β$69$, γ$70$]cats.data.EitherT[F,β$69$,γ$70$]]
and method catsDataBifunctorForEitherT in class EitherTInstances of type [F[_]](implicit F: cats.Functor[F]): cats.Bifunctor[[β$15$, γ$16$]cats.data.EitherT[F,β$15$,γ$16$]]
match expected type cats.Bifunctor[A.MyBifunctor] [25:21]
And unfortunately both:
- catsDataBifunctorForEitherT
- catsDataBitraverseForEitherT
are private so I can't provide one explicitly.
I found that issue trying to understand why I could do a leftWiden on :
EitherT[IO, ?, ?] and not on EitherT[Option, ?, ?]