[Fixed-point combinator in Swift] Fixed-point combinator (Z combinator) in Swift. Y combinator is not available, as Swift is a strict language. #demo

Zcombinator.swift

struct Fix<T> {
    let x: (Fix<T>) -> T
}

func fix<T, U>(f: @escaping (@escaping (T) -> U) -> ((T) -> U)) -> (T) -> U {
    { _fix in
        f { (_fix.x(_fix))($0) }
    }(
        Fix { _fix in
            f { (_fix.x(_fix))($0) }
        }
    )
}

let factorial: (Int) -> Int = fix { f in { n in n <= 0 ? 1 : n * f(n - 1) } }

print(factorial(10))