AppDelegate.swift

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

  var window: UIWindow?
  
  func addFoodTruck(foodTruckOptional: Result<FoodTruck>) {
    switch(foodTruckOptional) {
    case let .Error(error):
      println(error.description)
    case let .Value(boxedFoodTruck):
      let foodTruck = boxedFoodTruck.value
      println(foodTruck.name)
    }
  }

  func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    
    let url: NSURL! = NSURL(string: "https://rocky-ridge-2525.herokuapp.com/food_trucks")
    let getFoodTrucksRequest = NSURLRequest(URL: url)

    let getFoodTrucksTask = NSURLSession.sharedSession().dataTaskWithRequest(getFoodTrucksRequest) { data, urlResponse, error in
      
      // check for HTTP request errors
      if let err = error {
        self.addFoodTruck(.Error(err))
      }
      
      var jsonError: NSError?
      let jsonOptional: AnyObject! = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(0), error: &jsonError)
      
      // check for json parse errors
      if let err = jsonError {
        self.addFoodTruck(.Error(err))
      }
      
      if let jsonFoodTruckArray = JSONArray(jsonOptional) {
        for jsonFoodTruck in jsonFoodTruckArray {
          if let foodTruckDictionary = jsonFoodTruck >>> JSONDictionary {
            
            let foodTruck = FoodTruck.create <^>
              foodTruckDictionary["name"] >>> JSONString <*>
              foodTruckDictionary["day"] >>> JSONString <*>
              foodTruckDictionary["time"] >>> JSONString <*>
              foodTruckDictionary["location"] >>> JSONString
          }
        }
      }
      self.addFoodTruck(.Error(NSError()))
    }
    getFoodTrucksTask.resume()
    
    return true
  }

}

func JSONString(object: JSON) -> String? {
  return object as? String
}

func JSONDictionary(object: JSON) -> JSONDictionaryType? {
  return object as? JSONDictionaryType
}

func JSONArray(object: JSON) -> JSONArrayType? {
  return object as? JSONArrayType
}

typealias JSON = AnyObject
typealias JSONDictionaryType = Dictionary<String, JSON>
typealias JSONArrayType = Array<JSON>

struct FoodTruck {
  let name: String
  let day: String
  let time: String
  let location: String
  
  static func create(name: String)(day: String)(time: String)(location: String) -> FoodTruck {
    return FoodTruck(name: name, day: day, time: time, location: location)
  }
}

enum Result<A> {
  case Error(NSError)
  case Value(Box<A>)
}

final class Box<A> {
  let value: A
  
  init(value: A) {
    self.value = value
  }
}

infix operator >>> { associativity left precedence 150 }

func >>><A, B>(a: A?, f: A -> B?) -> B? {
  if let x = a {
    return f(x)
  } else {
    return .None
  }
}

infix operator <^> { associativity left }

func <^><A, B>(a: A?, f: A -> B) -> B? {
  if let x = a {
    return f(x)
  } else {
    return .None
  }
}

infix operator <*> { associativity left }

func <*><A, B>(f: (A -> B)?, a: A?) -> B? {
  if let x = a {
    if let fx = f {
      fx(x)
    }
  }
  return .None
}