refact.scala

def incr(i: Int): EvanderProcess[Int] = (i + 1).pure[EvanderProcess]

  def apply_n(events: List[Event]): EvanderProcess[List[Event]] = {
    val sorted = events sortBy (_.v)
    val received = sorted map (_.v)

    def msg(expected: Int, got: Int, version: Int) =
      "Event %d expected, but got %d instead (in events %s from version %d)".format(expected, got, received mkString ", ", version)

    for {
      version ← EvanderProcess.getVersion
      _ ← sorted.traverse(flowProcess) ! (version + 1)
    } yield sorted
  }
  
  type Version = Int
  def flowProcess(event: Event): StateT[EvanderProcess, Version, Unit] = {
    def before(event: Event) = for {
      x <- init[Version]
      _ <- LiftM(localVersion(x, go(x, event)))
      _ <- put(x + 1)
    } yield()
    
    def go(expected: Int, event: Event) = 
      if (expected > event.v) 
        skipped(msg(expected, event.v, version)))
      else if(expected < event.v) 
        fatalError[Int](msg(expected, event.v, version)
      else ().pure[EvanderProcess]

    before(event)
  }

s/msg/warn/ ?