const n = 1000

fn f(ch chan int) {
    mut s := 0
    for _ in 0 .. n {
        s += <-ch or {
            println('Something went wrong:')
            println('got ${err}')
        }
    }
    assert s == n * (n + 1) / 2
    ch.close()
}

fn do_send(ch chan int, val int) ?int {
    ch <- val?
    return val + 1
}

fn do_send_2(ch chan int, val int) ?int {
    ch <- val or { return error('could not send') }
    return val + 1
}

fn main() {
    ch := chan int{}
    spawn f(ch)
    mut s := 1
    for {
        s = do_send(ch, s) or { break }
    }
    assert s == n + 1
}