Alternative to Either[Error, Unit]

example.scala

import scala.util.{Either, Right, Left}

object MarkerExample {

  case class Error(msg: String)

  sealed trait Success // or "NoValue" or "SuccessWithNoValue"?
  object success extends Success {
    override def toString: String = "success"
  }

  def write(): Either[Error, Success] = {
    Right(success)
  }

  def log(): Either[Error, Success] = {
    Left(Error("in log"))
    //Right(success)
  }

  def run(): Either[Error, Success] =
    for {
      _ <- write()
      _ <- log()
    } yield success

  def run0(): Either[Error, Success] = {
    write().flatMap(_ => log())
    // Hurrah! Wont' compile -> write().map(_ => log())
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    import MarkerExample._
    println( run() )
  }
}