Data commit

Task/Monads-Maybe-monad/Swift/monads-maybe-monad.swift

@@ -0,0 +1,43 @@
+precedencegroup MonadPrecedence {
+	higherThan: BitwiseShiftPrecedence
+	associativity: left
+}
+
+infix operator >>-: MonadPrecedence	// Monadic bind
+
+typealias Maybe = Optional
+
+extension Maybe
+{
+	static func unit(_ x: Wrapped) -> Maybe<Wrapped>
+	{
+		return Maybe(x)
+	}
+
+	func bind<T>(_ f: (Wrapped) -> Maybe<T>) -> Maybe<T>
+	{
+		return self.flatMap(f)
+	}
+
+	static func >>- <U>(_ m: Optional<Wrapped>, _ f: (Wrapped) -> Maybe<U>) -> Maybe<U>
+	{
+		return m.flatMap(f)
+	}
+}
+
+func dividedBy2IfEven(_ x: Int) -> Maybe<Int>
+{
+	x.isMultiple(of: 2) ? x / 2 : nil
+}
+
+func lineOfAs(_ x: Int) -> Maybe<String>
+{
+	guard x >= 0 else { return nil }
+	let chars = Array<Character>(repeating: "A", count: x)
+	return String(chars)
+}
+
+print("\(Maybe.unit(6).bind(dividedBy2IfEven).bind(lineOfAs) ?? "nil")")
+print("\(Maybe.unit(4) >>- dividedBy2IfEven >>- lineOfAs ?? "nil")")
+print("\(Maybe.unit(3) >>- dividedBy2IfEven >>- lineOfAs ?? "nil")")
+print("\(Maybe.unit(-4) >>- dividedBy2IfEven >>- lineOfAs ?? "nil")")