Get Started

Functions & Methods

Function Declarations

fn add(a: Int, b: Int) -> Int {
    return a + b;
}

Functions that perform side effects must declare them:

fn save(data: String, path: String) ![io] {
    fs.write(path, data);
}

Methods

Methods are defined in impl blocks:

struct Circle {
    radius: Float,
}

impl Circle {
    fn area(&self) -> Float {
        return 3.14159 * self.radius * self.radius;
    }

    fn scale(&mut self, factor: Float) {
        self.radius = self.radius * factor;
    }
}

Closures

let double = |x: Int| -> Int { return x * 2; };
let numbers = [1, 2, 3].map(|n| n * 2);

Effect Propagation

Effects are transitive. If a function calls an effectful function, it must declare those effects:

fn helper() ![io] {
    print.info("helping");
}

// Must declare ![io] because it calls helper()
fn main() ![io] {
    helper();
}

The compiler provides fix-it hints when effects are missing.

Next Steps