Please note that

akka.actors.Channel trait does not exist in current akka versions
(available only in 1.3)

For the akka.actor.Channel trait removal after akk averisons 1.3,

see:
http://doc.akka.io/docs/akka/2.0/project/migration-guide-1.3.x-2.0.x.html

v1.3:

self.channel ! result
self.channel tryTell result
self.reply(result)
self.tryReply(result)
v2.0:

sender ! result

- Listing 10.4 uses case object Start that is not defined at Listing 10.3
- to be able to send synchronous messages you need to import
akka.pattern.ask (se
http://doc.akka.io/docs/akka/2.0/project/migration-guide-1.3.x-2.0.x.html)

Listing 10.1 uses _ to initialize a var, which has not been explained yet.