Together with PhD students Christophe Scholliers and Dries Harnie, I recently completed an operational semantics of our AmbientTalk programming language. We believe this is the first formal account of an actor language based on communicating event loops. The paper is currently available as a techreport. From the abstract:
We present an operational semantics of a key subset of the AmbientTalk programming language, AT-Lite. The subset focuses on its support for asynchronous, event-driven programming. AmbientTalk is a concurrent and distributed language that implements the so-called communicating event loops model.
Christophe has written an executable version of the operational semantics in PLT Redex. You can read all about that here.