Tour of Lux · chapter 1 of 8

Hello, Lux

Run your first program and read your first receipt.

Every cell on this tour is live — the code runs in your browser, in the Lux evaluator compiled to WebAssembly. Edit anything and press Run (or ⌘↵). Programs start at fn main():, and blocks are indentation-based, like the code reads.

fn main():
    println("Hello, Lux!")
    println("This ran in your browser.")

Strings interpolate with {braces} — any expression works inside them. Notice the receipt under the output: every run reports its evaluation steps and a modeled energy figure. In Lux, cost is an observable, not a mystery.

fn main():
    let name = "world"
    let year = 2026
    println("Hello, {name}!")
    println("In {year}, 2 + 2 is still {2 + 2}.")

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