Discuss: finite event streams, event data type

[dylemma]

Making event streams finite opens a lot of doors for new methods and capabilities on event streams. @nafg you've mentioned to me you like what bacon.js does, so following suit, we could have an Event data type along the lines of

/** base event type */
sealed trait Event[+T]

/** sent when `fire` is called */
case class Next[+T](item: T) extends Event[T] //aka Fire

/** maybe unnecessary for us, but represents an event error */
case class Error(cause: Throwable) extends Event[Nothing]

/** sent when the eventstream is finished, or when `stop` or
    some similar method gets called */
case object Done extends Event[Nothing]

/** this is how bacon.js sends the "current" value for their
    equivalent of a Signal, when an observer subscribes to it */
case object Initial[+T](item: T) extends Event[T]

Supposing eventstreams used Event[T] under the hood, we could implement things like ++ for stream concatenation, def end: Future[Time], and potentially clean up the Signal API by removing the current method as you had mentioned in conversation previously.