Result<A> meets flatMap

gistfile1.swift

//: Playground - noun: a place where people can play

import UIKit

public enum Result<A> {
    case Success(A)
    case Failure(NSError)
    
    public init(value:A) {
        self = .Success(value)
    }
    
    public init(error: NSError?) {
        if let error = error {
            self = .Failure(error)
        }
        else {
            self = .Failure(NSError(domain: "a", code: 0, userInfo: [:]))
        }
    }
    
    func open<T>(@noescape ifSuccess ifSuccess: A -> T, @noescape ifFailure: NSError -> T) -> T {
        switch self {
        case .Success(let value):
            return ifSuccess(value)
        case .Failure(let value):
            return ifFailure(value)
        }
    }
    
//    func open2<Result>(@noescape ifSuccess ifSuccess: A -> Result, @noescape ifFailure: NSError -> Result) -> Result {
//        switch self {
//        case .Success(let value):
//            return ifSuccess(value)
//        case .Failure(let value):
//            return ifFailure(value)
//        }
//    }
    
    func map<B>(@noescape transform: A -> B) -> Result<B> {
        return flatMap { .Success(transform($0)) }
    }
    
    public func flatMap<B>(@noescape transform: A -> Result<B>) -> Result<B> {
        return open(
            ifSuccess: transform,
            ifFailure: Result<B>.Failure)
    }
}

func hoge(input:Any) -> Result<String> {
    if let string = input as? String {
        return Result(value: string)
    }
    else {
        return Result(error: NSError(domain: "a", code: 0, userInfo: [:]))
    }
}

let a:Result<Any> = Result(value:10)
let b:Result<Any> = Result(value:"10")

/// error
a.flatMap(hoge).flatMap({Result(value:"Answer is \($0)")})

/// OK
b.flatMap(hoge).flatMap({Result(value:"Answer is \($0)")})

//
//func convertIt<A, T>(input:Result<A>) -> Result<T> {
//    switch input {
//    case .Success(let x):
//        if let value = x as? T {
//            return Result(value:value)
//        } else {
//            return Result(error: NSError(domain: "", code: 0, userInfo: [:]))
//        }
//    case let .Failure(error):
//        return .Failure(error)
//    }
//}
//
//func safeSqrt(input:Double) -> Double? {
//    return (input > 0) ? sqrt(input) : nil
//}
//
//let k:Int = 10
//
//
//
//let b:Result<String> = convertIt(a)
//let c:Result<Int> = convertIt(a)



//let array:[Double] = [10, 20, -1]
//
//for value in array.flatMap({safeSqrt($0)}) {
//    print(value)
//}
//
//for value in array.map({safeSqrt($0)}) {
//    print(value)
//}
//
//let d:Double? = 11
//let e:Double? = d.flatMap({safeSqrt($0).flatMap{safeSqrt($0)}})
//print(e)
//
//let f:Double????? = d.map({safeSqrt($0)})
//print(f)
//
////func convert<A,B>(t:Result<A>) -> Result<B> {
////    
////    t.map{
////        switch $0 {
////        case .Success:
////            return Result(error: NSError(domain: "a", code: 0, userInfo: [:]))
////        case .Failure:
////            return Result(error: NSError(domain: "a", code: 0, userInfo: [:]))
////        }
////    }
////    
////    return Result(error: NSError(domain: "a", code: 0, userInfo: [:]))
////}