// B1.2 — cancellation rides the `!` error channel (model (a)). `f.cancel()`
// sets the per-future cancel flag + marks `state = .canceled`, so a
// subsequent `f.await()` raises `error.Canceled` out of its value-failable
// `($R, !IoErr)` — caught here with `or`. A future that is NOT canceled
// awaits its value normally.
#import "modules/std.sx";

main :: () {
    // Not canceled → await yields the value.
    ok := context.io.async((n: i64) -> i64 => n, 7);
    print("ok: {}\n", ok.await() or { -1 });

    // Canceled → await raises .Canceled → the `or` default is taken.
    c := context.io.async((n: i64) -> i64 => n, 7);
    c.cancel();
    print("canceled: {}\n", c.await() or { -99 });
}