madsim VS mainspring

Being able to control nondeterminism is particularly useful for testing and debugging. This allows creating reproducible test environments, as well as discrete-event simulation for faster-than-real-time simulation of time delays. For example, Cardano uses a simulation environment for the IO monad that closely follows core Haskell packages; Sui has a simulator based on madsim that provides an API-compatible replacement for the Tokio runtime and intercepts various POSIX API calls in order to enforce determinism. Both allow running the same code in production as in the simulator for testing.

How Turmoil different from madsim? Is Turmoil a successor of madsim?

First off, awesome, interpreters and emulators are really fun projects. I've written a very similar project which might be useful for reference https://github.com/ncatelli/mainspring. As for parsing to your enum representation KerfuffleV2 gave a great example for nom. That being said, if you'd like to peek behind the curtain a bit for combinators and the principles behind nom, Bodil Stokke has a WONDERFUL tutorial on the topic https://bodil.lol/parser-combinators/ which will be directly applicable to what you are trying to do. Additionally, while targetted at using java, https://craftinginterpreters.com/ by Bob Nystrom is available for free online and covers the topic of writing really simple recursive decent parsers.