> designate the behavior to be used for the next message it receives. I think that is the key insight of actor-systems. Actors don't have state. But they can

> designate the behavior to be used for the next message it receives. I think that is the key insight of actor-systems. Actors don't have state. But they can calculate their replacement based on their immutable data. Thus the way an actor at a given address evolves is described by the functions that calculate the successor actors. Thus you get Pure Functional Programming implemented on top of a fabric of distributed evolving entities. You can understand the behavior and evolution of such a system as a composition of function-calls, where functions always produce the same result for the same arguments.