Shows how you can use `bind` and `reduce` to short circuit a bunch of mapping

BindThemAll.swift

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

import UIKit

public class Box<T> {
    let unbox: T
    init(_ value: T) {
        unbox = value
    }
}

public enum Result<T> {
    case Success(Box<T>)
    case Failure(String)
    
    init(_ value:T) {
        self = .Success(Box(value))
    }
}

extension Result {
    public func bind<U>(f: T -> Result<U>) -> Result<U> {
        switch self {
        case let .Success(value):
            return f(value.unbox)
        case let .Failure(error):
            return .Failure(error)
        }
    }
    
    public func fmap<U>(f: T->U) -> Result<U> {
        switch self {
        case let .Success(value):
            return .Success(Box(f(value.unbox)))
        case let .Failure(error):
            return .Failure(error)
        }
    }
}

func isOdd(x: Int) -> Bool {
    return x % 2 != 0
}

let numbers = Array(1..<10)
let oddNumbers = filter(numbers, isOdd)

func doubleOddNumber(x: Int) -> Result<Int> {
    println("Trying \(x)")
    if !isOdd(x) {
        return .Failure("\(x) is not odd")
    }
    else {
        return Result(x * 2)
    }
}

let result = reduce(numbers, Result([Int]())) { acc, number in
    acc.bind { (var array) in
        return doubleOddNumber(number).bind { oddNumber in
            array.append(oddNumber)
            return Result(array)
        }
    }
}

switch result {
case let .Success(value):
    let v = value.unbox
case let .Failure(message):
    println(message)
}

let result2 = reduce(oddNumbers, Result([Int]())) { acc, number in
    acc.bind { (var array) in
        doubleOddNumber(number).bind { oddNumber in
            array.append(oddNumber)
            return Result(array)
        }
    }
}

switch result2 {
case let .Success(value):
    let v = value.unbox
case let .Failure(message):
    println(message)
}