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Version 3 of Functional Wish Fulfillment
//
// Version 3 of pagesFromData from Functional Wish Fulfillment
// http://robnapier.net/functional-wish-fulfillment
//
import Foundation
func pagesFromData(data: NSData) -> Result<[Page]> {
return continueWith(asJSON(data)) {
continueWith(asJSONArray($0)) {
continueWith(secondElement($0)) {
continueWith(asStringList($0)) {
asPages($0)
}}}}}
func continueWith<A,B>(a: Result<A>, f: A -> Result<B>) -> Result<B> {
switch a {
case .Success(let boxA):
return f(boxA.unbox)
case .Failure(let err):
return .Failure(err)
}
}
func asJSON(data: NSData) -> Result<JSON> {
var error: NSError?
let json: AnyObject? = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(0), error: &error)
switch (json, error) {
case (_, .Some(let error)): return .Failure(error)
case (.Some(let json), _): return .Success(Box(json))
default:
fatalError("Received neither JSON nor an error")
return .Failure(NSError())
}
}
func asJSONArray(json: JSON) -> Result<JSONArray> {
if let array = json as? JSONArray {
return .Success(Box(array))
} else {
return .Failure(NSError(localizedDescription: "Expected array. Got: \(json)"))
}
}
func secondElement(array: JSONArray) -> Result<JSON> {
if array.count < 2 {
return .Failure(NSError(localizedDescription:"Could not get second element. Array too short: \(array.count)"))
}
return .Success(Box(array[1]))
}
func asStringList(array: JSON) -> Result<[String]> {
if let string = array as? [String] {
return .Success(Box(string))
} else {
return .Failure(NSError(localizedDescription: "Unexpected string list: \(array)"))
}
}
func asPages(titles: [String]) -> Result<[Page]> {
return .Success(Box(titles.map { Page(title: $0) }))
}
enum Result<A> {
case Success(Box<A>)
case Failure(NSError)
}
final class Box<T> {
let unbox: T
init(_ value: T) { self.unbox = value }
}
extension Result: Printable {
var description: String {
switch self {
case .Success(let box):
return "Success: \(box.unbox)"
case .Failure(let error):
return "Failure: \(error.localizedDescription)"
}
}
}
struct Page {
let title: String
}
extension Page: Printable {
var description: String {
return title
}
}
typealias JSON = AnyObject
typealias JSONArray = [JSON]
extension NSError {
convenience init(localizedDescription: String) {
self.init(domain: "", code: 0, userInfo: [NSLocalizedDescriptionKey: localizedDescription])
}
}
func asJSONData(string: NSString) -> NSData {
return string.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
}
let goodPagesJson = asJSONData("[\"a\",[\"Animal\",\"Association football\",\"Arthropod\",\"Australia\",\"AllMusic\",\"African American (U.S. Census)\",\"Album\",\"Angiosperms\",\"Actor\",\"American football\",\"Austria\",\"Argentina\",\"American Civil War\",\"Administrative divisions of Iran\",\"Alternative rock\"]]")
pagesFromData(goodPagesJson).description
let corruptJson = asJSONData("a\",[\"Animal\",\"Association football\",\"Arthropod\",\"Australia\",\"AllMusic\",\"African American (U.S. Census)\",\"Album\",\"Angiosperms\",\"Actor\",\"American football\",\"Austria\",\"Argentina\",\"American Civil War\",\"Administrative divisions of Iran\",\"Alternative rock\"]]")
pagesFromData(corruptJson).description
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