GoKawiilFor the past year and a half, the team building Roc's compiler has been rewriting our 300,000 lines of Rust code into Zig, for reasons I'll recap below. We recently passed an exciting milestone: feature parity with the original compiler!
Since the Bun project recently shared an experience report of their rewrite in the other direction (from Zig to Rust, although that's only the tip of the iceberg of differences between our rewrites), this seems like a nice time to reflect on how our move from Rust to Zig is going.
Hitting this milestone made it possible to update Brendan Hansknecht's charming 2024 WASM-4 game, Rocci Bird (with art by Luke DeVault) to use the new compiler. It's a nice example because the whole game is under a thousand lines of Roc code, and you can play it on itch.io or right here via WebAssembly:
Click or tap the game, then press Space (or tap) to flap. On mobile you don't have a right arrow key, so refresh the page to restart the game.
Rocci Bird's updated source code is a bit more concise than the original, and roc build --opt=size now outputs a 31KB wasm binary. (The original compiler produced a binary more than double that size.) Rocci Bird is by no means a large code base, but getting it to run at all required landing a lot of features in the new compiler. Seeing those chunky purple pixels brought a smile to my face when we finally got there!
To be clear, this is a milestone but not a formal release. (We aim to land version 0.1.0 later this year.) That said, it's a wonderful milestone to have reached, and I'm extremely grateful to all the people who came together to make this happen! I want to thank some in particular who have been especially helpful in getting the language and compiler to this point:
Thank you all so much! I feel honored that you've put so much of your valuable time into this project. Also thanks to our past and present sponsors—rwx, Lambda Class, ohne-makler, martian, tweede golf, Vendr, NoRedInk, and many generous individual sponsors—who have helped get us to this point by supporting our contributors.
Speaking of time: our 487-day rewrite took 476 days longer than Bun's 11-day rewrite from their ~500K lines of Zig into Rust. There are many reasons for this difference which have nothing to do with Rust or Zig, including the fact that theirs was a direct port whereas we'd decided to rewrite because of how much we were going to change. The techniques they used wouldn't have worked in our case.
The laundry list of changes we made also means comparing our original Rust code base and new Zig code base won't be apples-to-apples. Still, we've reached a nice point to reflect on how the rewrite has gone, both in terms of what new features it has unlocked for Roc programmers, as well as how our experiences with Rust and Zig have compared.
Let's get into it!
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