abstract class Pull[+F[_], +O, +R] object Pull: abstract class Terminal[+R] extends Pull[Nothing, Nothing, R] class StreamPullOps[F[_], O](self: Pull[F, O, Unit]): def flatMapOutput[F2[x] >: F[x], O2](): Pull[F2, O2, Unit] = self match case r: Terminal[?] => r case _ => ??? 

[error] ./test.scala:8:32 [error] Found: (r : Pull[F, O, Unit] & Pull.Terminal[_]) [error] Required: Pull[F2, O2, Unit] [error] [error] where: F is a type in class StreamPullOps with bounds <: [_²] =>> Any [error] F2 is a type in method flatMapOutput with bounds >: [x] =>> F[x] and <: [x] =>> Any [error] case r: Terminal[?] => r [error] ^ Error compiling project (Scala 3.8.0-RC1-bin-20250928-b67fcf2-NIGHTLY, JVM (21))