Interesting. Does that mean if you want to say, make an asynchronous http request, you do something like “fire_event(HttpRequestEvent(…))” which returns immediately, and somewhere else define a handler like “on_event(HttpResponseEvent, function (event) { … })” ? So you kind of have to manually break your function up into a state machine composed of event handlers? How do you associate a given HttpResponseEvent with a specific HttpRequestEvent?
It is a callback of sorts. But most languages do callbacks with some sort of anonymous closure mechanism (or more primitively, pass function pointer/identifiers). What makes BEAM interesting is its prevalence of generalizing callbacks themselves as more events (messages).
You can also define a callback function in, e.g., JavaScript, and pass its name instead of an anonymous closure. Does "BEAM" do anything that JavaScript can't or doesn't?
There are a few very large features that BEAM offers that, as far as I can tell, no other industrial language/VM implements. In particular, BEAM is meant for distributed computation.
You can spawn new processes, communicate between processes (which don't have to be on the same computer), sending any kind of data between them including closures.
BEAM also has an error model designed to handle concurrent and distributed failures, e.g. a process may fail and another process (which, again, may or may not be on the same machine) monitoring it may decide to restart it, or to do some recovery, etc.
BEAM builds into it a number of the features for which we use orchestration, observability, just simpler and (generally) more flexible. And this is a platform that has been used in the industry since the 90s.
Elixir IS very state machine like.
So yes, your event loop processes the results of asynchronous work launched because of earlier events the same way.
Part of what makes this work, is the awesome function clause matching. Coordinating origin of async work and result of async work is really easy because you can match on any form of terms your heart desires, and everything is always immutable.