Beni: A typed functional language for the browser, with no async/await

Beni creator here.

This is a language/research project. I want to explore what a combination of a purely functional language and a very advanced compiler is capable of generating in terms of JS.

One novel idea (AFAIK) is adding a borrow checker. Other languages targeting the browser have added borrow checkers, but that's been driven by WASM. In Beni, lists are immutable, but instead of being implemented using tries, they use regular JS arrays with in-place mutations. The borrow checker guarantees that ownership isn't shared and that it's safe to update them. One concern I have is that this could cause DX issues due to borrow checker errors. I don't think that's going to be an issue given that the language is functional, but it's still an open question.

The "Platforms" concept is an idea I borrowed from Roc, which also inspired many of Beni's design decisions. In Beni, you can't call JS directly, just like in Elm. Platforms wrap the JS ecosystem in a safe way so that it can be consumed by Beni. There's currently no way to install third-party JS libraries. I believe the NPM ecosystem is broken: even small libraries pull in hundreds of indirect dependencies. With AI, new CVEs are being found every week, and keeping `npm audit` clean has become a daily struggle.

The irony is that updating dependencies to fix these mostly harmless CVEs just increases the risk of supply chain attacks. My idea for Beni is to make it "batteries included" so that people need fewer third-party dependencies. For everything else, I think the correct approach is to vendor the code you need.

I used AI to verify the text of the post, but working with Beni has been fun, mostly because in the AI era the feedback loop makes a lot of difference. Otherwise you have to wait for ages to create things, like when using Rust for personal projects, which take a long time to compile. Even though the code in the end is fast, iterating on it kills the vibe, or it makes it hard because you need a lot of compute. And given the issues in the last few years with memory and computers being crazy expensive because of AI, having ways to iterate faster makes life a bit more pleasant.

It is also really good to focus on the problem and leave some of the things to AI, like proving that the ownership rules are sound with Lean, something I would maybe never be able to do without AI.