A small nitpick, Erlang doesn't implement the Actor model. The similarity of Erlang's processes and the actors, defined by Carl Hewitt, is accidental as stated by Joe Armstrong multiple times.
Edit: Actors doesn't run concurrently.
Edit: Actors doesn't run concurrently.
Why not? That's literally the whole point of the actor model; actors are definitionally units of concurrent computation. That's exactly why Hewitt based the actor model on how e.g. particles interact in physics - those interactions necessarily being concurrent.
That is:
> The similarity of Erlang's processes and the actors, defined by Carl Hewitt, is accidental as stated by Joe Armstrong multiple times.
Just because processes accidentally behave like actors doesn't mean they ain't actors.
Is that an actual law, or is it just that some implementations of the pattern are deficient? My impression is that the actor model was originally envisioned as being applied to a machine with hundreds or thousands of processors.
I think it'd be harder to make them run serially than concurrently, and of negative benefit.
Unless OP is saying this is some "rule" of being an Hewitt "Actor" in which case I'd call that somewhat arbitrary and unnecessary.