Writing a C Compiler, in Zig (2025)

ttosh about 8 hours ago 28 commentsRead Article on ar-ms.me

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Discussion (28 Comments)Read Original on HackerNews

fuhsnn•about 6 hours ago

Looking at the repo, the author seemed a little fed up [1] with the nature of lower level language and quitted.

[1] https://github.com/asibahi/paella/blob/main/writeup/c19.md#u...

MatthiasPortzel•about 3 hours ago

I’ve just read the two functions there by that footnote, `reaching_copies_meet`. I have so much code review feedback just on code style, before we even get into functionality. And it’s like 20 lines. (The function shouldn’t return an error set, it should take an allocator, the input parameter slices should be const, the function shouldn’t return either the input slice or a newly allocated slice.)

It’s interesting how Zig clicked for me pretty quickly (although I have been writing it for a couple of years now). But some of the strategies of ownership and data oriented design I picked up writing JavaScript. Sometimes returning a new slice and sometimes returning the same slice is a problem for memory cleanup, but I wouldn’t do it even in JavaScript because it makes it difficult for the caller to know whether they can mutate the slice safely.

I suspect that there’s a way to write this algorithm without allocating a temporary buffer for each iteration. If I’m right that it’s just intersecting N sets, then I would start by making a copy of the first set, and on each iteration, removing items that don’t appear in the new set. I suspect the author is frustrated that Zig doesn’t have an intersect primitive for arrays, but usually when the Zig standard library doesn’t have something, it’s intentionally pushing you to a different algorithm.

dwroberts•about 5 hours ago

Feels like maybe something lost in translation with their explanation - they say they were fed up of data structures etc. but they returned to Rust? I’m assuming there’s something a bit more nuanced about what they got tired of with Zig

namr2000•about 3 hours ago

Rust is a world away from Zig as far as being low-level. Rust does not have manual memory management and revolves around RAII which hides a great deal of complexity from you. Moreover it is not unusual for a Rust project to have 300+ dependencies that deal with data structures, synchronization, threading etc. Zig has a rich std lib, but is otherwise very bare and expects you to implement the things you actually want.

Ygg2•about 3 hours ago

This depends on what you mean by low level. Commonly it means, how much you need to take care about minute, low-level issues. In that way C, Rust, and Zig are about the same.

Dependencies have nothing to do with low-level vs. high-level but just package management, how well the language composes, and how rich the standard library is. Are assumptions in package A able to affect package B. In C that's almost impossible to avoid, because different people have different ideas about how long their objects live.

Having a rich standard library isn't just a pure positive. More code means more maintenance.

ecshafer•about 4 hours ago

I think Rust is "higher level" than C or Zig in the sense that there are most abstractions than C or Zig. Its not Javascript, but it is possible to program Rust without worrying too much about low level concerns.

flykespice•about 3 hours ago

Which is still a crazy claim considering Rust is often told about having strong bureaucracy around even sharing variables (borrow checker).

Ygg2•about 3 hours ago

Except if you need to expose or consume a C API, or you need to use some obscure performance improvement.

mrkeen•about 3 hours ago

The author was fed up with not having data structures already provided, and needing to roll his own

slopinthebag•43 minutes ago

While you can obviously write low level code in Rust and manage allocations, memory, use pointers etc, you can also write much higher level code leveraging abstractions both in Rust itself and its' rich ecosystem. If you're coming from higher level languages it's much friendlier than C/C++ or Zig. I think I would struggle to write C or Zig effectively but I have no issues with Rust and I really enjoy the language.

zengid•32 minutes ago

Quite a footnote [0]:

> I do not know if it is me being bored with the project, or annoyed with having to build and design a data structure, that has soured me on this project. But I have really at this point lost most motivation to continue this chapter. The way Zig is designed, it makes me deal with the data structure and memory management complexity head on, and it is tiresome. It is not "simpler" than, say, Rust: it just leaves the programmer to deal with the complexity, <strike-through>gaslighting the user</strike-through> claiming it is absolutely necessary.

[0] https://github.com/asibahi/paella/blob/main/writeup/c19.md#u...

flossly•about 5 hours ago

I thought Zig has a C compiler built in? Or is it just the Zig build system that's able to compile C, but uses an external compiler for that?

Still a proper programmer-flex to build another one.

spiffyk•about 5 hours ago

Zig actually bundles LLVM's Clang, which it uses to compile C with the `zig cc` command. But the long term goal seems to not be so tightly coupled to LLVM, so I'm expecting that to move elsewhere. They still do some clever stuff around compiler-rt, allowing it to be better at cross-compilation than raw Clang, but the bulk of it is mostly just Clang.

There is also another C compiler written in Zig, Aro[1], which seems to be much more complete than TFA. Zig started using that as a library for its TranslateC functionality (for translating C headers into Zig, not whole programs) in 0.16.

[1]: https://github.com/Vexu/arocc

Pay08•about 3 hours ago

They're not planning on dropping Clang.

Meneth•about 2 hours ago

They kinda are: "This issue is to fully eliminate LLVM, Clang, and LLD libraries from the Zig project." https://github.com/ziglang/zig/issues/16270

scatbot•about 6 hours ago

Cool project. Feels like writing a C compiler in Zig aligns nicely with the old "maintain it in Zig" idea that was part of Zig's early value proposition. Is that still considered a relevant goal today?

Longer term it also makes me wonder whether something like this could eventually reduce reliance on Clang/LLVM for the C frontend in zig's toolchain.

spiffyk•about 5 hours ago

There is actually another C compiler written in Zig, Aro[1], which Zig started using since 0.16 for its TranslateC module.

[1]: https://github.com/Vexu/arocc