Klujur

This is an LLM coded experiment. I don’t recommend actually using it. I was curious how far you can get prompting Claude Code (mostly Sonnet 4.5, some Opus 4.5) over a weekend to build something complex.

Klujur is an interpreted programming language modelled on Clojure. Klujur is written in Rust and intended to be useful as an embedded scripting language, but also ships with a standalone CLI REPL.

Demo

Installation

cargo xtask install

cargo will build and install the klujur executable, defaulting to ~/.cargo/bin.

Use

# Run with rlwrap wrapper
klj
# And with the bytecode VM
klj -b

# Or the unwrapped executable, if rlwrap is unavailable
klujur
klujur -b

Embedding

Add klujur-embed to your Cargo.toml:

[dependencies]
klujur-embed = { git = "https://github.com/waddie/klujur" }

use klujur_embed::{Engine, KlujurVal, Result};

fn main() -> Result<()> {
    let mut engine = Engine::new()?;

    // Evaluate code
    let result = engine.eval("(+ 1 2 3)")?;
    println!("{}", result); // 6

    // Register native functions
    engine.register_native("greet", |args: &[KlujurVal]| {
        let name = match args.first() {
            Some(KlujurVal::String(s)) => s.as_ref(),
            _ => "World",
        };
        Ok(KlujurVal::string(format!("hello, {}!", name)))
    });

    engine.eval("(println (greet \"Klujur\"))")?; // hello, Klujur!
    Ok(())
}

Using the Bytecode VM

Enable the bytecode compiler for improved performance:

use klujur_embed::{Engine, Result};

fn main() -> Result<()> {
    let mut engine = Engine::new()?;

    // Enable bytecode compilation mode
    engine.enable_bytecode_mode();

    // Functions are now compiled to bytecode and executed by a stack-based VM
    let result = engine.eval("((fn [x] (* x x)) 5)")?;
    println!("{}", result); // 25

    // Bytecode mode is particularly beneficial for:
    // - Recursive functions
    // - Tight loops
    // - Numerical computation
    let sum = engine.eval("(reduce + (range 10000))")?;
    println!("{}", sum); // 49995000

    Ok(())
}

Intended conventions

• .klj extension, or :klj key in .cljc files
• klj.edn project files

License

Copyright © 2025 Tom Waddington

Distributed under the MIT License. See LICENSE file for details.