Announcing Remacs: Porting Emacs to Rust

3 minute read

I am delighted to announce Remacs, a project to port Emacs to Rust!

Emacs, at its heart, is a lisp interpreter written in C. In Remacs, we’re replacing this C code with Rust, and all the elisp you know and love will just work.

If you’ve ever fancied contributing to core Emacs, this is a great opportunity to learn the internals. There’s tons of low hanging fruit, we have a list of good first bugs and even a walkthrough of writing your first elisp function using Rust.

Rust is perfect for this because we can port incrementally. If you want to replace the entire regular expression engine, you can do that. If you just want to replace this function here, you can do that and the C code won’t even notice. You will have a full-blown Emacs every step of the way.

Rust is also a terrific language to work with. The compiler, the autoformatter, the safety checks and the community all make for a great developer experience. Emacs support is pretty good too.

Why port to Rust? Porting to Rust gives us lots of opportunities. We can leverage the rapidly-growing crate ecosystem. We can drop support legacy compilers and platforms (looking at you, MS-DOS). We can add docstrings and unit tests to core functions that aren’t exposed to elisp. It’s also a ton of fun.

Remacs is based on Emacs 25.2. We’ve got enough type definitions that you can write interesting built-in functions, but the project is still at a very early stage. Using these, we’ve got a few built-in elisp functions written entirely in Rust: some arithmetic, some type checks, and even some basic list functionality.

If you’d like to join us, there’s plenty to do. You could:

Port a small C function in lisp.h to lisp.rs.

Port your favourite built-in elisp function to Rust.

If you’re feeling ambitious, we eventually want to explore:

Porting Remacs to the regex crate for a major performance speedup.

Using the existing GUI bindings crates.

We have a full list of project ideas here.

Naturally, we also provide Emacs propaganda, Rust propaganda, and a Travis-based workflow on GitHub. What are you waiting for? If you’ve ever wanted to hack on the world’s most powerful editor, we’d love you to join us!