//there is no "yield" for a plain
//sequence: "sequence" builds a lazy
//generator out of a closure
let counter = sequence(state: 3) {
    (current: inout Int) -> Int? in
    defer { current += 2 }
    return current <= 9 ? current : nil
}

for c in counter {
    print(c)
}
//printed 3, 5, 7, 9

//AsyncStream is the closest thing
//to a real "yield"
func makeCounter(low: Int, high: Int,
    step: Int) -> AsyncStream<Int> {
    AsyncStream { continuation in
        var current = low
        while current <= high {
            continuation.yield(current)
            current += step
        }
        continuation.finish()
    }
}

for await c in makeCounter(
    low: 3, high: 9, step: 2) {
    print(c)
}