Tour of Lux · chapter 4 of 8

Control flow

if/else, pattern matching, and loops.

match is an expression. Arms take literals, ranges like 1..10, guards with if, and a _ catch-all. Bound names are usable inside the arm.

fn describe(value: int) -> str:
    match value:
        0 => "zero"
        1..10 => "small"
        n if n > 100 => "large: {n}"
        _ => "medium"

fn main():
    println([0, 3, 50, 200] |> map(describe))

for iterates ranges (1..=10 is inclusive) and lists; while, break, and continue do what they say. The receipt below makes loop cost visible — try changing 1..=10 to 1..=1000 and watch the steps grow.

fn main():
    let mut total = 0
    for i in 1..=10:
        total = total + i
    println("sum 1..=10 = {total}")

    for word in ["lux", "joule", "watt"]:
        if word == "joule":
            continue
        println(word)

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