Event.scala

///////////////////////////////////////////////////////////////////////
// TOP SECRET METEORCODE ENGINEERING BULLSHIT -- DO NOT STEAL        //
// (c) Hawk Weisman, all rights reserved 'n' stuff                   //
///////////////////////////////////////////////////////////////////////
type Payload: Map[String,Object]

abstract class Event (
  protected val payload: Payload,
  protected var valid: Boolean = true
) extends (Payload)(prefunc: (Payload) => Boolean = {
  payload => return payload.seen(this)
}) => Unit {
    
  // validity stuff
  def isValid: Boolean = valid
  def invalidate: Unit { valid = false }
  
  // this is where you write the onEvent behaviour, basically - the 
  // closure body becomes the apply() method
  def apply(payload: Map[String, Object]): Unit 
  
  // onEvent applies the function to the payload (there might be a better way to do this)
  def onEvent(): Unit = if(prefunc(payload)) this(payload)
  
  // honestly we could just make it mix in abstract map and get all the nice map ops
  def patchPayload(key: String, value: Object) = payload put (key, value)
}

class Fireball(payload: Payload) 
extends Event(payload) { (payload) =>
  // do fireball stuff here
  println(payload.toString)
}

object EventDemo extends App {
  val aFireball = new Fireball(Map("some key" -> "some value"))
  aFireball.onEvent()
}

I think that the curried syntax may actually be

Payload => Prefunc => Boolean