Fibonacci

Recursion, an if-expression, and string interpolation — everything is an expression in Lux.

# Recursion, an if-expression, and string interpolation.
fn fib(n: int) -> int:
    if n <= 1:
        n
    else:
        fib(n - 1) + fib(n - 2)

fn main():
    print("fib(20) = {fib(20)}")

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Walkthrough

Everything is an expression: the if/else is the function body, and each branch yields the value — no return needed.
Type annotations (n: int, -> int) are optional everywhere; they are shown here for documentation. Inference fills them in when omitted.
String interpolation embeds any expression: "fib(20) = {fib(20)}".