Doo: A Simple, Fast Programming Language Built on Rust and LLVM
15 points - 11/03/2025
Hey HN!
https://github.com/nynrathod/doolang
I'm Nayan, and I'm stoked to share Doo, my project turned side hustle for a lang that's dead simple to write but punches like Rust. Think clean syntax (inspired by Rust but less boilerplate), auto memory mgmt via ref counting (no GC pauses), rich types, and it spits out standalone native bins via LLVM/clang.
Why Doo? Coding should feel fun, not fighty. No more wrestling with lifetimes or macros just to get a "hello world" but still safe and speedy.
Quick tour (hello.doo):
fn main() {
let msg = "Hey HN!";
print(msg);
}
Static Type System: Compile-time type checking with type inference
Automatic Memory Management: Reference counting for data types
Rich Data Types: Integers, strings, booleans, arrays, maps, and tuples
Module System: Organize code with a hierarchical import system
Control Flow: Conditional statements, for loops, and range iteration
Function System: First-class functions with parameter and return type annotations
Native Compilation: Compiles to standalone executables using clang/lld
Repo: https://github.com/nynrathod/doolang (stars/pulls welcome!)
What do you think? Too Rust-y? Missing a killer feature?
Great start!
Just want to say, you did all the right things: Simple instructions, to the point and, and I can't stress this enough - examples. Like 9/10 when someone shares their language, they have little to no examples and it's the first thing people ask for.
I do think you could probably have a few more examples that are like the calculator and less of what's basically a one liner.
On the language: I like what's there so far. It's clean minimalist, and familiar.
The problem is that there's not really a USP that I can see. I get the rust but with reference counting, but I don't think that's even close to enough. There has to be a really really good reason for people to try and use a new programming language. And I don't really see the overall vision beyond a small hobby project (which is fine if that's what you were aiming for)
> Missing a killer feature?
Yes, very much so.
Thanks for valuable feedback. Yeah definitely will add more examples projects.
And really make sense your point to have usp or any unique or good feature doolang should have. As this is just starting point of doolang, and honestly i never started this as hobby project I want this to be mature over years not to replace any languge but to have simplicity for writing servers and apis. after few months I will definitely integrate this with my own production note taking app once i improve this language.
Reference counting i Introduce for auto memroy mgmt only, as rust ownership and borrow method will be extreme complex to implement as solo dev i feel.
But now im clear now language should have any special feature or target which is lacking, idk what to find for this, but it will be valuable if you can suggest, im also thinking to have new post to ask feedback from community what they want in such language. Any suggestion?
> Doo provides a rich set of built-in types:
>
> Type Description Example
> Int 32-bit signed integer 42, -10
> Str UTF-8 string "Hello, World!"
> Bool Boolean value true, false
32-bit signed integer is the only numeric type in that "rich" set?!?
Good point, will remove that word, btw will added unsigned float in upcoming release. Thanks for that comment.
Very cool. I'm always on the lookout for languages - especially beginner-friendly ones - that are good candidates for building Wasm Components (my use case is a fantasy console with Wasm game cartridges).
Have you given any thought to supporting Wasm Components as a build target?
Doolang i started for writing server and apis easily and simply, but you points make sense for Wasm components. Not planned as of now as this is just starting point, but surely would take you thought for my further roadmap. Honestly i'm not too much expert in such thing yet, but would appreciate if you have any other more recommendations and suggestions
The idea and syntax looks good for me. I like it's clean an minimalistic design. But still it's to early to say is it good or not. Because there is no obvious features. You should answer the question what's the goal of the language and find the auditory who is right for you.
Did you write it or generate? If the later, then it's could be even more impressive in some way.
I think there is a bit of a additional value here. It's very good as a learning project, like "how to make you own programming language and compile it into executable". Due to the simplicity and minimalism, it could be very useful.
Hi,
Yeah make sense, but I don't have any buzzing goal right now, doolang is not any dsl, just to ensure high level syntax for developer writing backend servers apis. And not started as learning project. Will move forward as per feedback of community and requirement but not such specific target im aiming. so again simple concept is keep it simple to write with speed and security
I understand your intensions, but for compiled languages usually it takes years to be accepted by developers as a mature language. It is so even for Go and Rust. Both of them has giants behind them and, again, it took many years for them. As a solo developer you could make it more specific to become popular in some particular field and then to scale it. If the learning is too simple for you, then you can choose anything else. But if you wanna grow, turn it into product. If you want it to be more popular as a server side programming language you can add some language constructions to make it easy to write routers, parse requests data and react on it maybe with pattern matching. Hope this would help you to find your way to make it bigger. Good luck
True, it takes years. And as a solo dev its really hard. Turning into product really makes sense, i understood now i need something unique or specific feature. but as of now only writing apis routers and server with super simple syntax with speed and security only having in my mind. but I value your point, do you have any suggestions or recommendations? I'm also thinking to start new post to take ideas and suggestion from community.
what are the kind of things you are building yourself with this?
Hi,
So main goal of this language is to have simplicity while writing code. Rust is great will dominate, but as dev who want speed and security but with high level syntax, doolang is best for them. Right now im working on std library and inbuilt function, and moving forward I will integrate doolang with my own note taking app uoozer note https://play.google.com/store/apps/details?id=com.uoozer.not... , 550+ test cases covered by doolang already with valgrind memroy test too.
so for roadmap, after inbuilt functions and standard library deployment will build http router and will test real world scenario for api dev. IF all well then will integrate with uoozer note.
Is it safe?
Does it require using traits everywhere, like Rust does?
Does it have proper references (C++ style)?
Saying safe will be too early, but design philosophy is no compromise with security and speed with easy syntax. It passed with 550+ test cases including unit test, memory stress, integration, circular dep, regresssion, valgrind memory leak, fuzz testing, also i added conservative limits max depth for recursion and data length for stability. Find here https://github.com/nynrathod/doolang/blob/main/src/limits.rs
Doolang not uses any traits like rust. Rust is great language, but its expose everything in syntax that is also great but as developer who want security+speed with fast development may found issue writing rust, that is main goal of doolang simlicity. I'm still figuring out further design principle of syntax to have less exposing syntax.
Doolang have auto memory management with reference counting. Just simple mut keyword introduced for mutating variable let mut data = "data";
no other syntax expose all handling automatic with rc and auto type define if not defined explicitly
When I say safety I mean inability of the programmer to trigger UB using normal language features, like it's impossible in Rust and several other (less known) languages. Does Doo support it? Or I just can shoot the leg and compiler lets me do this?
About references: am I correct, that any value is reference-counted and one can pass it to a function and mutate it (the original, not a copy).
Doolang aims for memory safety with static typing and automatic reference counting, so you won't see classic C/C++ bugs. But it does not claim Rust's level of safety there’s no formal guarantee that safe code can't cause undefined behavior. It's quite safe in practice, just not as strict as Rust.
For complex types (strings, arrays, maps), values are reference-counted and passed by reference. If you pass such a value to a function, you're sharing the same object—mutations affect the original. For primitives (Int, Bool), it's pass-by-value (copy).
So, what if I want to pass a value of a primitive type by-reference?
How the equivalent code for the following C++ example looks like?
void Foo( int& x )
{
x= 123;
}
void Bar()
{
int x= 0;
Foo(x);
}
Doolang currently does not allow you to mutate a primitive variable from another function.
Only support this as of now
fn Foo(x: Int) {
x = 123; // Only modifies Foo's local copy
print("inside Foo", x); // Print 123
}
fn main() {
let x: Int = 0;
Foo(x);
// x is still 0 here after Foo returns
print("out x", x); // Print 0
}
But your points make sense, i should learn those UB works and will check how its behaving
Nooooo! "valgrind memory leak". Aaargh. Valgrind (memcheck) is not just a leak detection tool. Leak detection is so unimportant that it isn't even turned on by default.
Thanks for pointing that out. I didn’t actually know all the details about how Valgrind works under the hood just that it does memory checking. I'll definitely read up more on it. If you have any good resources or tips, I'd appreciate your suggestions!
Algebraic data types please. When you programme in Haskell, you use them all time, and yet support is missing in so many languages. It's one of the things that makes Swift look attractive to me.
Hi, thanks for pointing this out. Yeah struct and enum are alredy in pipeline. memroy mgmt and codegen work pending for those 2. Planning to release in 0.3.0 but let me see if possible on next release of 0.2.0
Struct enums are base of any type safe language will surely add in upcoming releases.