Almost five years ago, Saoirse “boats” wrote “Notes on a smaller Rust”, and a year after that, revisited the idea.
The basic idea is a language that is highly inspired by Rust but doesn’t have the strict constraint of being a “systems” language in the vein of C and C++; in particular, it can have a nontrivial (or “thick”) runtime and doesn’t need to limit itself to “zero-cost” abstractions.
What languages are being designed that fit this description? I’ve seen a few scripting languages written in Rust on GitHub, but none of them have been very active. I also recently learned about Hylo, which does have some ideas that I think are promising, but it seems too syntactically alien to really be a “smaller Rust.”
Edit to add: I think Graydon Hoare’s post about language design choices he would have preferred for Rust also sheds some light on the kind of things a hypothetical “Rust-like but not Rust” language could do differently: https://graydon2.dreamwidth.org/307291.html
Haskell.
I’m not joking. If you want something that’s very similar to Rust, but doesn’t have the restriction of being a systems language, then Haskell might be the right thing for you. Unlike Rust, Haskell is Pure Functional though, so it forces you to have an even cleaner architecture.
If Pure Functional isn’t your beer, then you could also check out the language that inspired Rust: ML. If I remember correctly, Rust was started as “something similar to ML, but suitable for systems programming”. So, it only feels natural to take an ML dialect if you want “something similar to Rust, but without the restriction of it being suitable for systems programming”.
A popular ML dialect would for instance be F#, which is built on top of the .Net runtime and is therefore compatible with C# and the likes. On the other hand, in order to make it compatible with C# and the likes, there are some weird compromises in F#…
Or, if you (like me) dislike the idea of having a Garbage Collector, you could go for Lean4. That’s what I’m learning currently, and it feels a bit like a bastard child of Haskell and ML.
Although I’m fully in camp functional, I doubt that. There are problems that are inherently stateful and rely on mutability. Modelling that in Haskell often results in unnecessary abstractions. I think Rust hits a sweet spot here (when you’re that experienced to write idiomatic Rust, whatever that exactly is). Also being lazy by default has its own (performance) implications, strict + lazy iterators (like Rust) is a good default IMO.
Im surprised you didn’t mention OCaml or Elm
OCaml seems really close, but I’m told that there are problems with its concurrency story. I do think it sounds like a really good language.
I’m curious if you were told that recently. I know that there have been stable releases of major features and libraries concerning concurrency and parallelism near the end of 2022. It may be much improved since you your source last looked. Or it could be a limitation in the implementations of these.
My understanding was that there’s some ecosystem bifurcation, somewhat like Rust’s. But I’ll look into it again!
Oh, yeah. The Jane Street vs non-Jane Street library incompatibilities still exist. But there is a new concurrency library that was made such that the need to use monads has been eliminated.
I did mention ML, of which OCaml is a dialect. Afaik Elm doesn’t have type classes (aka Traits) - a property I would consider necessary to call it “similar to Rust”.
Fair points.
I do want to learn Haskell some day, but it seems like it has a whole different set of reasons why it’s tricky to learn; and I hear enough about the more complex features (e.g. arrow notation) having compiler bugs that I think it really doesn’t sound like a “smaller” or “simpler” language than Rust.
That said, yeah, it definitely meets the criteria of having strong typing, a functional style, a garbage collector, and pretty good performance.