Guide

Pattern matching

match/case destructures values — and the compiler proves your match is exhaustive before it ever runs.

fn label(n: Int) -> Text:
    match n:
        case 0:
            return "zero"
        case 1:
            return "one"
        case other:
            return "many ({other})"

fn main() -> Void:
    print(label(0))
    print(label(7))

Patterns: literals, the wildcard _, bindings, Some/None/Ok/Err, record patterns with all fields, and qualified enum variants. A match on an Option must cover Some and None; a match on an enum must cover every variant — or end with an irrefutable arm.

fn size_class(n: Int) -> Text:
    match n:
        case v if v > 100:
            return "large"
        case v if v > 10:
            return "medium"
        case v:
            return "small ({v})"

fn main() -> Void:
    print(size_class(500))
    print(size_class(50))
    print(size_class(5))

Guards (since Sprint 22): a pattern may carry an if condition, checked after the pattern matches with its bindings in scope. The guard must be Bool — no truthiness — and a false guard falls through to the next arm. Guarded arms never count toward exhaustiveness, so the checker still demands an unguarded arm for every case.