Your first Rhai mod

A Rhai mod is a folder with two files. Make mods/my_mod/ with this mod.toml:

name = "my_mod"

[oxidizer]
script = "main.rhai"

and this main.rhai:

fn init() {
    print("my_mod: hello!");
}

fn gui(dt) {
    if begin("My mod") {
        let v = ksa::Program::controlled_vehicle();
        if v == () {
            text("no vehicle");
        } else {
            text(`flying ${v.id} at ${v.get_barometric_altitude().to_int()} m`);
        }
    }
    end();
}

Start the game (or, if it is already running, wait a second: Oxidizer starts new Rhai mods by itself). A window called My mod shows the vehicle you fly, and my_mod: hello! is in Mods > Oxidizer's log.

Now change the text in main.rhai and save the file. Within a second the window shows your change, without restarting anything. That loop, save and look, is how Rhai mods are written.

Three ways to start

• By hand, as above.
• Rhai Studio, an editor inside the game: type a name, press CREATE, and a starter mod is running; edit it with syntax colors and save with Ctrl+S.
• The Rhai mod template on GitHub: a repository with a starter mod, a release workflow and a content index listing ready to fill in. Clone it straight into the mods folder and edit it with your editor.

Rhai in one minute

Rhai reads like Rust without the types:

let speed = 12.5;                 // variables
let name = "Gemini";              // strings; `...${x}...` in backticks interpolates
let parts = [1, 2, 3];            // arrays
let info = #{ id: 1, ok: true };  // object maps

if speed > 10.0 { print("fast"); } else { print("slow"); }
for p in parts { print(p); }

fn twice(x) { x * 2 }             // the last expression is the return value

Integers and floats are different types: 1 + 1.0 is an error, write 1.0 + 1.0 or to_float(1). The Rhai book has the whole language.