Functions

A function is a reusable piece of code that takes zero or more inputs and has a single output.

fn distance(x1, x2, x2, y2) {
    sqrt((x2 - x1) ^ 2 + (y2 - y1) ^ 2)
}

Functions can be recursive.

fn fibonacci(n: int) -> int {
    if n < 2 {
        n
    } else {
        fibonacci(n-2) + fibonacci(n-1) // recursive calls to fibonacci()
    }
}

The last expression in the body of the function is the return value. You can also return early from a function. If a function's body doesn't have a last expression, the function returns void, which is nothing.

fn fibonacci(n: int) -> int {
    if n <= 1 {
        return n            // early return
    }
    fib(n-2) + fib(n-1)     // last expression is return value
}

fn display_message() -> void {
    for n in range(5) {     // last statement is a for loop. No return value
        println(n)
    }
}

For convenience, if a function body is just a single expression, the body can be written after an equal sign = instead of being wrapped in a curly brace block:

fn distance(x1, x2, x2, y2) = sqrt((x2 - x1) ^ 2 + (y2 - y1) ^ 2)