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When Rust is the right tool

21 April 2026·2 min read

Image processing, parsing, a fast library from crates.io. A .qwer file is Rust, used like a .qwe file, with its functions callable from Quillo.

Some work belongs in a systems language: decoding images, parsing a binary format, a library that only exists in Rust. A web language should not pretend otherwise, and should not make the bridge a project of its own.

A Rust file, used like any other

//! [dependencies]//! image = { version = "0.25", default-features = false, features = ["jpeg"] }/// How bright a picture is, from 0 to 255.pub fn brightness(path: &str) -> Result<f64, String> {    let img = image::open(path).map_err(|e| e.to_string())?.to_luma8();    Ok(img.pixels().map(|p| p.0[0] as f64).sum::<f64>() / img.len() as f64)}

use "imaging.qwer"route GET /photos/:name = { brightness: brightness(`photos/${name}.jpg`)? }

A .qwer file is Rust. Its top-level pub fns become the program's functions, its dependencies are listed at the top, and Quillo builds it.

Values cross as they are

Integers, floats, bools and strings cross directly, Vec becomes a list, HashMap<String, T> a map, Option<T> the value or null. A Result becomes the value or an error value, so ? and ?? work on Rust failures exactly as on Quillo's. For anything richer, serde_json::Value carries it.

Where to draw the line

Crossing costs a conversion each way, so the bridge suits functions that do a lot of work per call: decoding an image, not adding two numbers. And for arithmetic, Quillo can often be fast enough on its own.

Read more: Rust in the docs.