@lucy @snacks I'll mainly speak about Elixir but it's based on BEAM, the Erlang's VM.
You can hot reload module (a functions pack) during execution.
I don't really understand what are those callbacks but it's doable.
To have many processes (a few thousand) is totally common and normal. If you don't use those you are missing the point.
It exists ports, a way to connect Elixir to another programs in another language
I don't know if it's help you but if you *really* needs muti tasking, Elixir/Erlang is the way to go (or Go but I never used it all, only heard legends)