typealias Promise<Value> = (@escaping (Value) -> ()) -> () とする Promisure (= Promise + Closure) というライブラリも作ってましたｗ// Wrapping let a: Promise<Int> = { $0(3) } // like `Promise.resolve(3)` in JS // Promisifying a callback let b: Promise<Int> = promise { resolve in // Gets 5 after 1.0 seconds DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) { resolve({ $0(5) }) } } // Operators let sum: Promise<Int> = a >>- { a in b >>- { b in { $0(a + b) } } } // flatMap let square: Promise<Int> = { $0 * $0 } <^> a // map let vector: Promise<Vector2> = curry(Vector2.init) <^> { $0(2.0) } <*> { $0(3.0) } // apply