Compare Publisher.publish

  def publish(e: Event) { for (l <- listeners) l(e) }

and Reactions.Impl.apply

  def apply(e: Event) {
    for (p <- parts) if (p isDefinedAt e) p(e)
  }

This means that if we have the following code

    val l: Reaction = {
      case ButtonClicked(b) => println("Button pushed")
    }
    // This should work, or not be available in the API ;)
    button.subscribe(l)
    // This works
    button.reactions += l

it will give lots of MatchErrors (e.g. when FocusGained/FocusLost events are fired) if we add the listener with the first construct, whereas it works fine in the second construct.

(Actually, why are there two different ways of adding listeners in the first place?)