Explore additional Box combinators and hierarchical improvements

A few possibilities:

• Add collect to Box. This can be useful for PartialFunction-based combined filter+map operations on boxes as they are on collections.
• Add some sort of mapFailure that behaves similarly to map but only runs with a Failure. This would allow running a function only when the box is a Failure, without having to do a match that has to deal with the other three box states.
• Restructure the Box hierarchy a little to allow a type that indicates “only Empty or Full” and another that indicates “only Failure or Full”, for example.
• Add logging helpers for Box if possible (may need to be in lift-util).

For the last one, an untested proposal I posted to gitter a while back:

sealed trait Box[+T]
sealed trait PresenceBox[+T] extends Box[T]
sealed trait TryBox[+T] extends Box[T]
sealed abstract class EmptyBox extends Box[Nothing] // Empty or Failure
case class Failure(msg: String, exception: PresenceBox[Throwable], chain: PresenceBox[Failure]) extends EmptyBox with TryBox[Nothing]
case object Empty extends EmptyBox with PresenceBox[Nothing]
case class Full[T](item: T) extends TryBox[T] with PresenceBox[T]

[Bhashit]

Alright. I think I’ll create a small WIP PR soon. Maybe you can comment on relevant parts, whether or not it’s what you expected and I’ll make the necessary changes. Hopefully that won’t be too much trouble for you. But do let me know if that doesn’t work for you.

[Shadowfiend]

No, I think flip handles flipFailure just fine—it takes an EmptyBox, but if you want to pattern match inside it you can. I guess it won’t let you only flip a Failure… I would say it’s worth waiting to see if that’s a material use-case in practice though.