Consider making Delta[F[A]] ~= F[B]

[stacycurl]

I'm planning on making Delta[scala.xml.Node] == scala.xml.Node & Delta[Json] == Json, so this could be applied more generally.

Example Set(1, 2).delta(Set(2, 3)) currently is SetPatch(added = Set(3), removed = Set(1)), it could be Set((Added, 3), (Removed, 1)) (SetPatch could extend Set to provide both).

Similarly Map(1 -> 1, 2 -> 2).delta(Map(2 -> 22, 3 -> 3)) == MapPatch(removed = Map(1 -> 1), added = Map(3 -> 3), changed = Map(2 -> 2.delta(22))), it could (almost) be Map(Removed -> Map(1 -> 2), Added -> Map(3 -> 3), Changed -> Map(2 -> 2.delta(22))).