scan-example.scala

sealed trait State { def count: Int }

case class Odd(count: Int) extends State
case class Even(count: Int) extends State
case class Emit(count: Int) extends State

val scanned =
  observable.scan(Empty : State) { (state, elem) =>
    val newState = state match {
      case Odd(count) =>
        val s = if (elem % 2 == 1) Odd(count+1) else Even(1)
      case Even(count) =>
        if (elem % 2 == 0) Even(count+1) else Odd(1)
      case Emit(_) =>
        if (elem % 2 == 0) Even(1) else Odd(1)
    }

    if (newState.count > 100)
      Emit(newState.count)
    else
      newState
  }

scanned.collect { case Emit(n) => true }