Roc lang to be rewritten in Zig

yamafaktory · February 4, 2025, 8:55pm

gist.github.com

https://gist.github.com/rtfeldman/77fb430ee57b42f5f2ca973a3992532f

rewrite.md

This may become a blog post or FAQ entry or something. For now, I'm just writing up something to answer the questions I've gotten about it!

## Rewriting a Language's Compiler in Itself

Scratch-rewriting a code base in a different language is usually considered a risky move that often leads to failure. In the case of compilers, it's the reverse; most successful compilers (e.g. Java, C++, C, C#, TypeScript, Scala, Go, Rust, Zig, OCaml, Haskell, and [many others](https://en.wikipedia.org/wiki/Self-hosting_(compilers)#List_of_languages_having_self-hosting_compilers)) have undergone a complete scratch-rewrite...in themselves. This process is called [self-hosting](https://en.wikipedia.org/wiki/Self-hosting_(compilers)).

We can break down the observation that self-hosting has a long track record of success into two pieces:

1. It's normal for a successful language's compiler to be rewritten from scratch in a different language.
2. It's normal for the different language to be the target language itself.

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Calder-Ty · February 4, 2025, 10:14pm

A frustratingly common response I’ve heard to this complaint is that “several seconds is not as bad as [some other language or some other project that has minutes-long build times]!” I don’t care if things could be even worse, I care that I’m feeling this pain while knowing I don’t have to. Zig’s x86-64 backend can reportedly scratch-build (without anything cached) the entire 300K-line Zig compiler code base in a second or two. It takes us longer than that to build one of our medium-sized Rust crates, and that’s even with the benefit of caching.

I can be sympathetic to that frustration. However is it True that zig can build itself that fast? I’ve never actually built zig, just used the distributed binary.

tobyjaffey · February 4, 2025, 10:16pm

This video (which I watched yesterday by coincidence) explains a lot of the thinking here about how Zig is used in the Roc compiler. https://youtu.be/jIZpKpLCOiU?si=T1TZRN-DzFNCeWmQ

TUSF · February 4, 2025, 10:16pm

Presumably, he’s talking about the custom x86_64 backend, which is only for debug builds, does not use LLVM directly, and doesn’t support a number of things, afaik, but it is extremely fast to compile, otherwise.

pierrelgol · February 5, 2025, 6:51am

yes I’ve tried it and it’s really fast, even on my laptop which isn’t a beast by any stretch of the imagination it’s really good.

gonzo · February 5, 2025, 8:01am

Love these news. Left a comment in the gist too.

pierrelgol · February 5, 2025, 10:52am

I think it’s pretty close to parity to other backends in term of features support, at least on the issue tracking, there isn’t much left to implement for parity

mperillo · February 10, 2025, 11:12am

This video may be related:

kristoff · February 10, 2025, 8:34pm

I interviewed Richard Feldman on the rewrite today on Zig SHOWTIME.

yamafaktory · February 10, 2025, 8:36pm

Awesome! Adding this gem to my watchlist! Thanks!