Functions & closures

Declare with fn. return is optional; a function with no return yields nil.

fn add(a, b) {
    return a + b
}
print(add(2, 3))       # 5

Functions are first-class values and close over their defining scope:

fn make_counter() {
    let count = 0
    fn tick() {
        count += 1
        return count
    }
    return tick
}

let c = make_counter()
print(c())             # 1
print(c())             # 2
print(c())             # 3

The number of arguments must match the number of parameters (there are no default or variadic parameters for user functions).