Curious: Did implementing this in Rust expose any bad or interesting behavior when replicating the Erlang language spec (https://github.com/erlang/spec) or whatever reference implementation you were targeting?
It was kind of interesting exploring the OTP internals, especially some of the parts that haven't changed in a long time. One example is the PAM: I think it stood for "patrick's abstract machine" and it would compile erlang terms into bytecode for pattern matches (intended for fast ETS lookups). It's all there in one file and it took a fair bit of digging to figure out how it works since it's been static for a long while and nothing on the internet really documented it.
If this is still the case you should definitely consider contributing to the documentation of those files. Odds are they'll be used by the next person to try something similar. :)
Edit: this book is available for free here: https://www.microsoft.com/en-us/research/publication/the-imp...
I have heard similar before at an Erlang meetup. Are there elements of the VM you encountered that were also static and lacking sufficient documentation? I'm guessing much of this is just tribal knowledge deep inside Ericsson then? It would be great if there were a public repository for these things.
From my own experience, those parts that are commented or documented tend to clarify some specific design constraints (for example, why processes have multiple locks on different parts, and why they are locked in a specific order, or the rationale of the carrier design); but you never really get a clear picture of why things overall are architected the way they are overall, what designs were considered and discarded due to some deficiency, what tradeoffs were made, etc. I think much of the actual content like that which may exist, is either buried in the minds of the original engineers, or in some internal documentation at Ericsson that has never been released. My suspicion is that you'd need to dig through mountains of emails and such to piece together a more complete picture of how things where put together over time.
It's also the fact that the BEAM just has a lot of really complex pieces built in to it after all this time. Everything from binary pattern matching and construction, to garbage collection and memory management, ETS, Mnesia, etc. Each one of those things is not only non-trivial, but have evolved significantly over time, through the hands of many engineers. It also doesn't help that large portions of the C implementation are written in an extremely macro heavy style, which makes it quite hard to read without knowing what all the macros do and how they play together.
Projects like Enigma, or Lumen, have a lot to give back to the community in the form of documenting how these pieces are built. Unfortunately, the lack of a specification for the Erlang language and its runtime, means it is very much a grind to work out how things are currently implemented, and why.
I'm also not saying that the C code is unmaintainable. It's definitely a bear to dive into, but by spending enough time with it, it starts to unfold in front of you. The main issue I have, is that none of the specification/design documentation exists as part of the source repository. Maybe it doesn't exist at all, but in that case, I'd really hope that some of those core engineers would have taken the time to write some of that stuff down. In any case, none of it is readily available AFAIK.