Builds an rx tree.

Builder.scala

object Builder {
  implicit def rx2tree(rx: Rx[_]) = show(rx)

  sealed trait RxTree
  final case class Branch(rx: Rx[Any], branches: RxTree *) extends RxTree
  final case class RxBranch(rx: Rx[Any], input: RxTree, branches: Rx[Option[RxTree]]) extends RxTree
  final case class Leaf(rx: Rx[Any]) extends RxTree

  val flatMapStreams = mutable.Map[FlatMap[_, _], Rx[Option[RxTree]]]()

  def show[A](rx: Rx[A]): RxTree = rx match {
    case Map(self, _)              => Branch(rx, self)
    case fm @ FlatMap(self, _)     => {
      RxBranch(rx, self, flatMapStreams(fm))
    }
    case Zip(self, other)          => Branch(rx, self, other)
    case DropRep(self)             => Branch(rx, self)
    case Merge(self, other)        => Branch(rx, self, other)
    case Foldp(self, _, _)         => Branch(rx, self)
    case Collect(self, _, _)       => Branch(rx, self)
    case SampleOn(self, other)     => Branch(rx, self, other)
    case Imitate(self, other)      => Branch(rx, self, other)
    case Sharing(self)             => Branch(rx, self)
    case leaf: Var[A]              => Leaf(leaf)
  }

  def spyFlatMaps[A](rx: Rx[A]): Rx[A] = rx match {
    case fm @ FlatMap(r, f) => {
      val v = Var[Option[RxTree]](None)
      val g = FlatMap(r, { x =>
        val res = f(x)
          v := Some(res)
        res
      })
      flatMapStreams(g) = v
      g
    }
  }
}