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
I didn’t love that article - Rust isn’t strictly a systems language. It’s general purpose, and a lot of the mechanics are very useful for general programs.
I feel like you may have missed the point, then? Or at least interpreted the article very differently? Rust isn’t “strictly” a systems language, but neither is C or C++; people use them for application development all the time. But all three languages have very specific limitations (most obviously, that adding a garbage collector would be an unwelcome change) imposed by the need to fulfill the “systems” niche.
Compare Golang: it can’t replace C++ for every use-case, because it has a garbage collector, and because you need cgo to use FFI. But it’s otherwise a very flexible language that can be used for most types of software.
What I would like to see is something that shares these advantages with Go:
- quick to build
- easier to teach & learn than Rust
- easier to quickly prototype with than Rust (though of course it’s debatable how well Go does at this one)
…but I don’t like the actual language design of Go, and I think it’s possible to design a language that’s more Rusty but still simpler than actual Rust.
For instance, error handling in Rust is both more ergonomic and more rigorous than in Go. That’s huge! A language like Go but with sum types, Result, and the question-mark operator would be leaps and bounds nicer than Go itself.
To be clear, I don’t imagine that a “smaller Rust” would replace Rust. But I also don’t think we’ve reached optimal language design when the language I’d pick to write an OS is also the language I’d pick to write a small CLI app.
The designers of Go actually discussed civilised error handling (like Rust and others), but in order to make it useful they’d have to include other features like ADTs and something like an Either monad (Result type), which they felt would make Go too difficult to learn for the developers they envisioned Go to be used by.
One of the most important reasons for the popularity of Go is exactly that it is extremely limited, and can be picked up by any developer in a few hours. It takes no time to learn because there is nothing there that would need to be learned. This isn’t a limitation, it’s a feature (opinion of Go designers, not mine).
The key point here is our programmers are Googlers, they’re not researchers. They’re typically, fairly young, fresh out of school, probably learned Java, maybe learned C or C++, probably learned Python. They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt.
- Rob Pike
Jeeze, I knew that simplicity was the goal (and I think they largely succeeded in that), but that quote is so explicitly condescending. “They’re not capable of understanding a brilliant language”?
I disagree slightly with the need to add full ADT support to the language to implement that style of error handling, because Pike et al. had no problem adding “special cases” to the language: in particular, return values are essentially tuples, but that’s the only place in the language with that concept. So they wouldn’t need to introduce user-definable enums and full pattern-matching to have better error handling. I can think of a couple approaches they could have used:
- Use compound-return-values as they currently exist, but have additional compiler-enforced restrictions:
- There can be at most one
errorvalue in the return types, and it must be the last element in the “tuple” - when returning a non-nil
error, the other values must be zero/nil - the compiler would require all errors to be checked, never ignored (Go should have at least done this, even without the other stuff)
- Add the question-mark operator, which would do basically the same thing as in Rust: check if the error value is
nil, discard it if so, return early if not
- There can be at most one
- Have a special “result” type that is quasi-generic (like slices and maps) and treated as a sum-type by the compiler, but which can only be used as a return value from functions. Provide some special variant of the
switchstatement to destructure it (akin to how type switches have their own bespoke syntax/keyword).
Rust is a groundbreaking language, but it’s not without tradeoffs. There are loads of things it makes extremely difficult compared to slightly higher level languages.
I used it happily for years, but I wouldn’t recommend it for any project that didn’t explicitly need the low-level performance optimisation.
Extremely hard disagree on the last statement. It certainly has tradeoffs, but they are almost all very valuable to many general applications which don’t need performance at all. I’ve been using it professionally for a very long time now and migrated multiple companies from JS, Python, Java, and C# to Rust and it brought huge advantages.
I believe you, but for it to be a fair comparison you’d need to compare to an alternative rewrite, not to the original software.
Rust has plenty of merits. It has a very readable functional style, single aliasing to reduce complexity, powerful libraries for stuff like generating serialisation code, and cargo is incredible.
However, expressing any complex graph structure in Rust is just painful, and so is refactoring code. Small changes in intent require complex reworking of data structures, because Rust forces you to be extremely specific about data layouts at all times. These issues crop up constantly in any complex project, and they really slow things down.
Although Rust is a nice language, you can now write functional code with immutable data structures in pretty much any modern, statically-typed language. C#, Kotlin, Scala, Swift, etc. It will be concise, quick to write, easy to modify and pretty fast at runtime.
Perhaps I’m mistaken in some way, but this has been my honest experience after many years using Rust.
Why would you want that? What is wrong with python if you want an interpreted language with garbage collection? By contrast what is wrong with rust + a lot of crates (or C++/Ada/…) if you want a compiled language?
Zero cost abstractions are great because speed is very important for complex problems. Little things here and there make for modern computers that feel slower than my old 8 bit atari when trying to get work done.
There is a huge and valuable possibility space between python and Rust. We know this because it is already occupied by many extremely successful languages (Java, C#, Swift, etc).
The value of a language that sits between C# and Rust also seems pretty obvious at this point; a language that gives you Rust’s memory management tools for optimisation, but doesn’t force you to use them for all of your code.
It exists, it’s called Rust with lots of Arc, .clone(), and Box. You don’t have to borrow if you prefer to have a slower, easier program.
I know Rust has these features, but they are intended to be features of last resort and it shows. It’s not a criticism; Rust pushes people relentlessly towards safety and performance, and is extremely successful at that.
I am imagining a language more like Pony, but with less of a focus on the actor model. I could use a language like that to write a high performance game engine with no GC pausing issues, and then write very high level gameplay scripts on top of it in the same language.
You could do that in Rust, but the Rust game engine space has already made it clear that most people feel the need for a scripting language.
Box
Now try to do that with a trait that isn’t object-safe…
I get your point, these things make fighting with the borrow-checker a little bit less annoying, but Rust is complex. I’ll happily accept that because I value high code-quality (to that point that I rather invest more time to get things right) but when that is not the goal and you want something higher-level and strongly-typed there are alternatives that work better (I’m just talking about the language itself, ecosystem alone for me is yet another pro-Rust thing)
Coming from some one who used 4 different languages (C#, C++, Python, and G’MIC), I just feel more comfortable when there’s a explicit end blocks, which is why I don’t like Python. Of all of those languages, only Python does not make that explicit end block which is off-putting in my opinion, and there isn’t any other options with the similar role to Python.
Copying what I wrote in another comment:
What I would like to see is something that shares these advantages with Go:
- quick to build
- easier to teach & learn than Rust
- easier to quickly prototype with than Rust (though of course it’s debatable how well Go does at this one)
…but I don’t like the actual language design of Go, and I think it’s possible to design a language that’s more Rusty but still simpler than actual Rust.
For instance, error handling in Rust is both more ergonomic and more rigorous than in Go. That’s huge! A language like Go but with sum types, Result, and the question-mark operator would be leaps and bounds nicer than Go itself.
To be clear, I don’t imagine that a “smaller Rust” would replace Rust. But I also don’t think we’ve reached optimal language design when the language I’d pick to write an OS is also the language I’d pick to write a small CLI app.
Learning a programming language is not hard. there are thousands of choices. Before you ask for another one, first please check that there isn’t already one that meets your needs. Fragmentation of languages is not useful in general. It is rare to have an idea that hasn’t been tried before, so find someone who already has done that idea.
… I am currently asking if there is a language that fits the description. And I’m clearly not the only one interested in such a language.
I personally have not found Rust onerous to learn, especially by comparison to C++. But a lot of people do find the learning curve steep.
You mean a interpretative language with similar role to Python, but more like Rust/C++ style? I actually want that so that I can ditch Python even if I learned it and use this instead.
Not necessarily interpreted, but possibly. I think a more likely path is something like Go that’s compiled but still has a garbage collector.
If you use a garbage collector the whole borrow checker would not make any sense.
Do you want to have error handling and functional paradigms in go? I think you should start there and ask go Devs why their language is lacking such basic stuff.
I spend an inordinate amount of time at my C# day job adding documentation comments about exclusive access and lifetimes and ownership… things which are clearly important but which dotnet provides little or no useful support for, even though it has a perfectly good garbage collector. The dotnet devs were well aware that garbage collection has its limits, especially when interacting with resources managed outside of the runtime, and so they added language features like IDisposable and finalisers and GCHandle and SafeHandle and so on to fix some of the things GC won’t be doing for you.
I’d happily use a garbage collected language with borrow checking.
Not sure if this is what OP is seeking, but I would be fine to have borrow checker removed, replaced with Garbage collector like Go/Python in such a language.
To build prototypes, I don’t want to fight with borrow checker and neither I care for efficiency much. But I do want the macro system, traits, lazily asynchronous runtime, cargo like package manager, easy build system, etc.
Rust has so many powerful features, but only because of borrow checker (IMO) we can’t use it for rapid prototyping like Python. With that replaced, this subset of Rust would be something which can be a great contender to Python/Go, etc.
F#? It’s compiled, statically typed, somewhat fast, garbage-collected, and supports Rust-style error handling
The biggest difference I see is allowing multiple mutable borrows, which would make a lot of things easier, but aside from that it sounds like it would have most of the same usability problems as Rust.
I’m also a bit put off when I see LLVM advertised as the primary compiler back-end these days. Pretty much guarantees slow builds.
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.
have an even cleaner architecture
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.
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.
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”.
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.
