Thanks for your interest.

Note Moonbit is a language/platform for industrial usage(not an academic language), I contributed to OCaml so that I am familiar with the good/bad parts of a type system. Its aim is to build fast and run fast, and generate the tiny Wasm output.

Type system is sound, you can take it as Rust(- some features hinder fast compilation) with GC and an emphasis on data oriented programming, so we have ADT, generics, interface and ad-hoc polymorphism. We also plan to make the pattern match more expressive with first class pattern support.

The async story is constrained by the WASM runtime, we will evolve with the Wasm proposal.

I thought the raison d’être for Rust was not having a GC. If this is a garbage collected language, and requires a runtime for such, isn’t this more like Go or any JVM language?

They're just talking about the type system. Yes the type system in Rust serves it's GC-free goals but you could copy paste the type system and build other languages with different goals.

Arguably the raison d’être for Rust is memory safe systems programming, and opt-in GC you implement as / if needed is just a consequence of that… if you’re not targeting the very small subset of systems that _cannot_ benefit from automated GC then that’s a great choice, but for everyone else it’s just complex boilerplate. This is aimed at an evolving runtime spec that already incorporates opt-in GC.

In other words if it’s Rust’s broader features but explicitly meant to write programs for a runtime that already includes opt-in GC, then it’s not doing what JVM languages or Go are doing, so there’s space for it.

For situations where you can afford a GC, Rust but with GC would be an excellent language, due to the ways macros are done, traits work, how errors are handled, tools like cargo, docs.rs, testing and doctests, self-contained binaries with additional ability to compile extra assets into them, high quality language server (rust-analyzer), and the quality of the ecosystem.

As it is now, though, regrettably Rust imposes on you the penalty of dealing with borrowing and ownership even when there is no reason to pay for that. Its not too bad in most cases but one can't help but imagine a Rust-but-with-GC world :)

For that world there is also Rhai (https://github.com/rhaiscript/rhai), TypeScript, Scheme, etc.

Though Moonbit does look nice too.

> one can't help but imagine a Rust-but-with-GC world

Rust with reference counting gets you a long way there. I’ve leaned in Rc<> a ton in some projects and had a pretty great experience.

I built https://github.com/mmastrac/keepcalm/ to specifically give "permission" to use ref-counting to make your life easier. For a webserver, references don't make any sense and really don't add anything measurable from a performance perspective.

That’s awesome. I do think someone smarter than me needs to write a “Pragmatic Rust” book, or something. The complexities around references and lifetimes put a lot of people off but really aren’t necessary a lot of the time.

If you want some of the ergonomics and DX of Rust, but in a GC'd language, OCaml (the language also used to implement early Rust compilers) might be more the path to be taken. Great tooling, handlings errors in sensible ways, and pattern matching, allows you to move business logic faster and focus on shaping data rather than transforming the bytes of them.