Swift Async functions

gistfile1.swift

func mapParallel <A, B> (values: [A], task: ( (A, (B) -> () ) -> () ), callback:([B]) -> ()) {
    
    let tasks: [((B) -> ()) -> ()] = values.map({
        v in
        return {
            cb in
            task(v, cb)
        }
    })
    
    return parallel(tasks, callback)
}

func parallel <A> (tasks: [((A) -> ()) -> ()], callback:([A]) -> ()) {
    
    var arr = Array<A?>(count: tasks.count, repeatedValue: nil)
    var add: (Int, A) -> () = {
        i, v in
        arr[i] = v
        
        var newArr = [A]()
        for a in arr {
            if a != nil {
                newArr.append(a!)
            } else {
                return
            }
        }
        callback(newArr)
    }
    
    for (i, t) in enumerate(tasks) {
        t({a in add(i, a)})
    }
}