Is there a good general-ish purpose scripting language (something like Lua on the smaller end or Python on the bigger) that’s implemented in only Rust, ideally with a relatively low number of dependencies?
Have you used it yourself, if so for what and what was your experience?
Bonus points if it’s reasonably fast (ideally JITed, though I’m not sure if that’s been done at all in Rust).
Sure you could JIT Rust, the question is if you can write a JIT compiler in rust since it needs to do some quite scary stuff to swap in compiled routines when evaluating code. I’m not even sure if unsafe is enough for that, you may need goto or arbitrary function pointers (which is kind of the same thing)
I originally meant solution described here:
https://blog.cloudflare.com/using-go-as-a-scripting-language-in-linux/
Considering most JIT compilers for JavaScript are written in C++, I can’t conceive of a reason you couldn’t implement one in Rust.
Is part of your requirement that
unsafedoesn’t get used anywhere in the dependency tree? If so you’d have to take away most of the Ruststdlibrary since many implementations in there have small strategic uses ofunsafeunder the hood.In my entire software engineering career, which spans embedded systems to CAD applications, I’ve never encountered a case where
GOTOis actually needed (but maybe some places where it can be used as a dirty shortcut to save you some lines of code).As for arbitrary function pointers, if those function pointers are written in Rust then they’ll come with all the safety assurances afforded to Rust code. I suppose if you’re worried about the danger of running ussr-code with
unsafein it, you could probably have your JIT refuse to compile theunsafekeyword specifically.The only part of a JIT compiler I don’t understand how it works is the part that swaps in compiled routines during interpretation. That’s the point I’m unsure of how to write in Rust because it seems like it would require very custom control flow. It might be that you can handle this by storing your compiled instructions somewhere using the C calling convention and then having Rust call your compiled function like a C function.
In essence, what you have is a Rust program that has to produce machine code (easy!), store it somewhere in RAM (also easy, I think), and then somehow call it (how???). The final part seems like the difficult one since passing execution into arbitrary memory they just wrote is just the sort of thing programs aren’t normally supposed to do.