One of the single most important things I've done in my career was going down the Actor Model -framework rabbit hole about 8 or 9 years ago, read a bunch of books on the topic, that contained a ton of hidden philosophy, amazing reasoning, conversations about real-time vs eventual consistency, Two-Generals-Problem - just a ton of enriching stuff, ways to think about data flows, the direction of the flow, immutability, event-logged systems and on and on. At the time CQS/CQRS was making heavy waves and everyone tried to implement DDD & Event-based (and/or service busses - tons of nasty queues...) and Actor Model (and F# for that matter) was such clean fresh breath of air from all the Enterprise complexity.
Would highly recommend going this path for anyone with time on their hands, its time well spent. I still call on that knowledge frequently even when doing OOP.
On the BEAM used by Erlang, Elixir, and Gleam actors are called processes, and this guide [1] delves into domain modeling with them.
[0] https://fraktalio.com/fmodel/
[1] https://happihacking.com/blog/posts/2025/the-gnome-village/
These days I would recommend picking a framework and then ask claude & friends to do a deep dive with you and build an example project out. Ask it to explain concepts, architecture, trade-offs, scalability considerations, hosting considerations, compare it with other frameworks, hook it up to storage systems (sqlite, postgresql, blob storage) and so on. Try running them within a wireguard network and so on. Very interesting learning to be found.
The Axum language had `domain` types, which could contain one or more `agent` and some state. Agents could have multiple functions and could share domain state, but not access state in other domains directly. The programming model was passing messages between agents over a typed `channel` using directional infix operators, which could also be used to build process pipelines. The channels could contain `schema` types and a state-machine like protocol spec for message ordering.
It didn't have "classes", but Axum files could live in the same projects as regular C# files and call into them. The C# compiler that came with it was modified to introduce an `isolated` keyword for classes, which prevented them from accessing `static` fields, which was key to ensuring state didn't escape the domain.
The software and most of the information was scrubbed from MS own website, but you can find an archived copy of the manual[1]. I still have a copy of the software installer somewhere but I doubt it would work on any recent Windows.
Sadly this project was axed before MS had embraced open source. It would've been nice if they had released the source when the decided to discontinue working on it.
[1]:https://web.archive.org/web/20110629202213/http://download.m...