AsyncFor.swift

import Foundation

func asyncFor<T>(_ initial: T, _ condition: @escaping (T) -> Bool, _ update: @escaping (T) -> T, _ body: @escaping (T, @escaping () -> Void) -> Void, _ done: @escaping () -> Void) {
    var state = initial
    var next: (() -> Void)!

    next = {
        body(state, {
            state = update(state)
            if condition(state) { next() }
            else                { done() }
        })
    }

    next()
}

asyncFor(0, { $0 < 10 }, { $0 + 1 }, { i, next in
    DispatchQueue.main.async {
        print(i)
        next()
    }
}, {
    print("done")
    exit(0)
})

RunLoop.current.run()

Output:

0
1
2
3
4
5
6
7
8
9
done