Node.js like event-loop with libdispatch and Swift

nodelike.swift

#!/usr/bin/env xcrun swift

import Dispatch

let appQueue = dispatch_queue_create("org.tkareine.NodeLike.appQueue", DISPATCH_QUEUE_SERIAL)
let appGroup = dispatch_group_create()

func delay(delayInMS: Int, block: () -> Void) {
    let delayInNS = Int64(delayInMS) * Int64(NSEC_PER_MSEC)
    let scheduleAt = dispatch_time(DISPATCH_TIME_NOW, delayInNS)
    dispatch_group_enter(appGroup)
    dispatch_after(scheduleAt, appQueue) {
        block()
        dispatch_group_leave(appGroup)
    }
}

func defer(block: () -> Void) {
    dispatch_group_async(appGroup, appQueue, block)
}

/*
 * The event loop. The joke is that the loop is implicit: we're using a
 * serial queue from libdispatch and waiting for all events scheduled to
 * it to complete.
 */
func run(block: () -> Void) {
    defer {
        block()
    }
    dispatch_group_wait(appGroup, DISPATCH_TIME_FOREVER)
}

println("testing...")

var results: [Int] = []

for i in 0..<10 {
    run {
        defer {
            results.append(1)

            delay(200) {
                results.append(4)

                delay(200) {
                    results.append(6)
                }
            }
            delay(100) {
                results.append(2)

                defer {
                    results.append(3)

                    delay(200) {
                        results.append(5)
                    }
                }
            }
        }

        results.append(0)
    }

    assert(results == [0, 1, 2, 3, 4, 5, 6])

    results.removeAll()
}

println("ok!")