TailRec.swift

TailRec.swift

class TailRec<A> {
    fileprivate init() { }
    
    func flatMap<B>(_ f: @escaping (A) -> TailRec<B>) -> TailRec<B> {
        return FlatMap(self, f)
    }
    
    func map<B>(_ f: @escaping (A) -> B) -> TailRec<B> {
        return flatMap { a in  Return(f(a)) }
    }
}

final class Return<A>: TailRec<A> {
    let a: A
    init(_ a: A) {
        self.a = a
        super.init()
    }
}

final class Suspend<A>: TailRec<A> {
    let resume: () -> A
    
    init(resume: @escaping () -> A) {
        self.resume = resume
        super.init()
    }
}

final class FlatMap<A, B>: TailRec<B> {
    let sub: TailRec<A>
    let k: (A) -> TailRec<B>
    
    init(_ sub: TailRec<A>, _ k: @escaping (A) -> TailRec<B>) {
        self.sub = sub
        self.k = k
    }
}