guoye-zhang

func toPeano(_ n: Int) -> Any {
    precondition(n >= 0)
    if n == 0 {
        return nil as Any?
    } else {
        return toPeano(n - 1) as Any?
    }
}

protocol OptionalProtocol {

guoye-zhang

func i(_ condition: Bool, then: () -> ()) -> (() -> ()) -> () {
    func run(_ condition: Bool) -> (() -> ()) -> () {
        return { _ = condition && $0() as Any is () }
    }
    run(condition)(then)
    return run(!condition)
}

// Usage:
let els = i(true) {