Consume a capture

A reusable closure borrows its captured state on each call. Sometimes the purpose of the callback is to hand over an owned value. Mark that callback once:

def main() -> Result[(), AllocError | IoError]:
    values = [2, 3, 5]?
    take = def once [values]() -> list[i64]:
        values
    result = take()
    print(result)?
    Ok(())

[2, 3, 5]

take() consumes the callback and transfers its captured list to the result. A second call is a use-after-move error. If take is never called, dropping it cleans up the list.