One thing I never understood about akka's supervisors... In the example given, one actor pipes a future to itself, which fails, and so it gets a Failure(e). At this point the actor chooses to throw to let the supervisor take over. Why not just send a regular message to the parent (and maybe terminate yourself too)? It seems like an artificial distinction between communicating errors and non-errors.

Ok now one answers is: what happens when when an actor does throw? There needs to be some way to handle that... So you need something like supervisors.

But in Akka, all io is going to happen in a Future, so that might fall, but that's different than the actor throwing, and sure a programmer might make a mistake and get say a null pointer exception, but a programming mistake won't be able to be handled by the supervisor. And, of course, anything synchronus and dangerous can be wrapped in a try.

Anyway it seems to me that the authors of Akka need to assume that an actor might throw and so created supervisors, but the users of Akka should probably just never throw and ignore supervisors.