scalaz.syntax.all._ doesn't work for MonadState/MonadError implicit parameters list.

[kczulko]

Hi,

I made an example app here: https://github.com/kczulko/scalaz-mtl-issue showing what's the problem.

When I create a function like this:

def dummyProgram[F[_]](implicit ME: MonadError[F,Throwable], MS: MonadState[F,Int]): F[Unit] = {
    for {
      i      <- MS.get
      _      <- MS.put(i + 1)
      result <- if (i < 0) ME.raiseError(new Throwable(":/")) else ME.point(())
    } yield result
  }

and try to materialize it with the following code:

  def main(args: Array[String]): Unit = {
    implicit val etme = EitherT.eitherTMonadError[Id,Throwable]
    implicit val stms = StateT.stateTMonadState[Int, EitherT[Id,Throwable,?]]
    implicit val stme = StateT.stateTMonadError[Int,EitherT[Id,Throwable,?],Throwable]

    dummyProgram[StateT[EitherT[Id,Throwable,?],Int,?]]
      .run(2)
      .run
      .fold(l => println(s"error: $l"), r => println(s"success $r"))
  }

Program doesn't compile with the first error of: value flatMap is not a member of type parameter F[Int]

But when I move MS as explicit parameter:

def dummyProgram[F[_]](MS: MonadState[F,Int])(implicit ME: MonadError[F,Throwable]): F[Unit] = ...

and call the program appropriately:

dummyProgram[StateT[EitherT[Id,Throwable,?],Int,?]](stms)

it compiles.

Am I doing sth wrong here?
Thanks in advance,
Karol

scalaz version: 7.2.26

~$ java -version
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-8u181-b13-1ubuntu0.16.04.1-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)

[xuwei-k]

#1110 ?