Guards and or-patterns

Separate top-level alternatives with |. Every alternative must bind the same names with the same types. Add if condition after a pattern to require a guard.

Guards run only after the pattern matches. They do not make a match exhaustive, so keep an unguarded case for every remaining value.

fn classify(value: int) -> string {
  match value {
    x if x < 0 => "negative",
    0 | 1 | 2 => "small",
    _ => "large",
  }
}

fn main() {
  println(classify(-1))
  println(classify(2))
}