I find this resource confusing and annoying to read. When performing my thesis research I wasted a bunch of time trying to make sense of Hewitt's writing. I think a big problem is that the term "actor model" is so overloaded that it almost becomes meaningless. The actors that Hewitt is talking about is not at all the same as Erlang or Akka. As an example I consider this quote from the text nonsensical "Actor systems…
Probably, the most fundamental misunderstanding of the Actor Model is that it is based on "Event Loops" which require the following: When an Actor receives a message, it must run until it produces a response to the message and then loops back to receive another message. However, a ReadersWriter scheduler must be able to receive more read and write messages even while it is still processing a message as explained in https://www.amazon.com/Inconsistency-Robustness-Studies-Logi...
Even so, a ReadersWriter scheduler must obey the Mutual Exclusion Principle, which says that only one activity can execute in an Actor at a time.
Another common misunderstanding is that an an Actor must have a mailbox, message queue, or event queue. There would be an infinite regress if any of these were required because since everything is an Actor, each of these would itself need a mailbox, message queue, or event queue!