1. How to use Functional
Reactive Programming
without Black Magic

2. let me = Person(name: "Jens Ravens")
@JensRavens
GitHub: JensRavens
nerdgeschoss.de
swift.berlin

3. A short introduction to
functional programming, the
universe and everything.

4. In the beginning McIlroy
created the unix pipe. And he
saw it was good.
ls | grep *.jpg | sort

5. Application Architecture

7. starting from a blank slate

8. implement to understand

9. And I promise not to use the
scary M-word.
me, 12 weeks ago.

10. How to train
your monad.

11. –Saunders Mac Lane
All told, a monad is just a monoid in the
category of endofunctors.
“

12. Monads are just Applicative Functors
“

13. ls | grep *.jpg | sort

14. Buy it, use it,
break it, fix it,
Trash it, change it,
mail - upgrade it.
– Daft Punk, Technologic

15. Buy it;
if error {
//TODO: Handle me!
} else {
use it;
if error {
//TODO: Handle me!
} else {
break it;
if error {
//TODO: Handle me!

16. ls | grep *.jpg | sort

17. Monad
something that defines map and bind

18. The optional Monad
let string: String? = "World"
let greeting = string.map{"Hello ($0)”}
//Hello World
extension Optional {
func bind<U> (f: T->U?) -> U? {
if let result = self.map({f($0)}) {
return result
} else {
return nil
}
}
}

19. The optional Monad
let string: String? = "World"
let greeting = string.map{"Hello ($0)”}
//Hello World
func greetOrNil(name: String)->String? {
if name == "World" {
return "Hello World"
} else {
return nil
}
}
let greeting2 = string.bind(greetOrNil)
//Hello World

20. The optional Monad
extension Optional {
func bind<U> (f: T->U?) -> U? {
if let result = self.map({f($0)}) {
return result
} else {
return nil
}
}
}
extension Optional {
func bind<U> (f: T->Optional<U>) -> Optional<U> {
switch self {
case let .Some(value): return f(value)
case .None: return nil
}
}
}

21. The result Monad
public enum Result<T> {
case Success(Box<T>)
case Error(NSError)
}

22. The result Monad
public enum Result<T> {
…
public func map<U>(f: T -> U) -> Result<U> {
switch self {
case let .Success(v):
return .Success(Box(f(v.value)))
case let .Error(error): return .Error(error)
}
}
…
}

23. The result Monad
public enum Result<T> {
…
public func bind<U>(f: T -> Result<U>)
-> Result<U> {
switch self {
case let .Success(v): return f(v.value)
case let .Error(error): return .Error(error)
}
}
…
}

24. ls | grep *.jpg | sort
Monad
Transform

25. func parseString(data: NSData) ->
Result<String>
func parseJson(data: NSData) ->
Result<[String: AnyObject]>
func asyncGreeting(name: String,
completion: Result<String>->Void)

26. public func bind<U>(f:(T, (Result<U>->Void))->Void)
-> (Result<U>->Void)->Void {
return { g in
switch self {
case let .Success(v): f(v.value, g)
case let .Error(error): g(.Error(error))
}
}
}

27. Interstellar

28. ls | grep *.jpg | sort

29. public final class Signal<T> {
private var value: Result<T>?
private var callbacks: [Result<T> -> Void] = []
public func subscribe(f: Result<T> -> Void) {
if let value = value {
f(value)
}
callbacks.append(f)
}
public func update(value: Result<T>) {
self.value = value
self.callbacks.map{$0(value)}
}
}

30. public func map<U>(f: T -> U) -> Signal<U> {
let signal = Signal<U>()
subscribe { result in
signal.update(result.map(f))
}
return signal
}
public func bind<U>(f: T -> Result<U>) -> Signal<U> {
let signal = Signal<U>()
subscribe { result in
signal.update(result.bind(f))
}
return signal
}

31. public func bind<U>(f: (T, (Result<U>->Void))->Void)
-> Signal<U> {
let signal = Signal<U>()
subscribe { value in
value.bind(f)(signal.update)
}
return signal
}

32. pushing instead of pulling

33. the rise of custom
operators

34. infix operator >>> { associativity left precedence 160 }
public func >>> <A,B> (left: Signal<A>,
right: A->Result<B>) -> Signal<B> {
return left.bind(right)
}
public func >>> <A,B>(left: Signal<A>,
right: (A, (Result<B>->Void))->Void) -> Signal<B>{
return left.bind(right)
}
public func >>> <A,B> (left: Signal<A>, right: A->B) ->
Signal<B> {
return left.map(right)
}

35. ls | grep *.jpg | sort

36. ls | grep *.jpg | sort
ls >>> grep("*.jpg") >>> sort

37. But what about
Threads?

38. public final class Thread {
public static func main<T>(a: T, completion:
T->Void) {
dispatch_async(dispatch_get_main_queue())
{
completion(a)
}
}
public static func background<T>(queue:
dispatch_queue_t)(_ a: T, _ completion: T->Void)
{
dispatch_async(queue){
completion(a)
}
}
}
ls >>> Thread.background(queue) >>> grep("*.jpg")
>>> sort >>> Thread.main

39. Extending UIKit to
support Signals.

40. var SignalHandle: UInt8 = 0
extension UITextField {
public var textSignal: Signal<String> {
let signal: Signal<String>
if let handle = objc_getAssociatedObject(self,
&SignalHandle) as? Signal<String> {
signal = handle
} else {
signal = Signal("")
NSNotificationCenter.defaultCenter().addObserver(self,
selector: Selector("textChanged:"), name:
UITextFieldTextDidChangeNotification, object: self)
objc_setAssociatedObject(self, &SignalHandle,
signal,
objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN_NONATOMIC))
}
return signal
}
public func textChanged(notification: NSNotification) {
textSignal.update(.Success(Box(self.text)))
}
}

41. If it’s variable, it qualifies
as a Signal.

42. ReactiveKitten
It’s about gifs. And cats.
And gifs of cats.

43. userTyping >>> createURL >>> loadRequest
>>> parseData >>> mainThread >>>
displayCats
The transform, the cat
and you.

44. import Interstellar
private func request(path: String, completion: Result<NSData>->Void)
{
let url = NSURL(string: baseURL.stringByAppendingString(path))!
let request = NSURLRequest(URL: url)
session.dataTaskWithRequest(request){ data, response, error in
if error != nil {
completion(.Error(error))
} else if let response = response as? NSHTTPURLResponse {
if response.statusCode >= 200 && response.statusCode<300 {
completion(.Success(Box(data)))
} else {
completion(.Error(NSError(domain: "Networking", code:
response.statusCode, userInfo: nil)))
}
} else {
completion(.Error(NSError(domain: "Networking", code: 500,
userInfo: nil)))
}
}.resume()
}

45. private func parseJSON(data: NSData)
->Result<[String: AnyObject]> {
var error: NSError?
if let json =
NSJSONSerialization.JSONObjectWithData(data, options:
nil, error: &error) as? [String: AnyObject] {
return .Success(Box(json))
} else {
return .Error(error!)
}
}

46. let imageSignal = gifSignal >>> getURL >>>
Thread.background >>> loadFromCache >>>
retryFromNetwork >>> Thread.main

47. class ViewController: UIViewController {
var signal: Signal<[Gif]>!
let searchBar = UISearchBar()
override func viewDidLoad() {
super.viewDidLoad()
navigationItem.titleView = searchBar
signal = searchBar.textSignal >>>
Network().search() >>> Thread.main

48. github.com/jensravens/reactivekitten

49. What’s next()?

50. Functors, Applicatives
and Monads in Pictures.
http://adit.io/posts/2013-04-17-
functors,_applicatives,_and_monads_in_pictures.html

51. The Introduction to RP
you’ve been missing.
https://gist.github.com/staltz/868e7e9bc2a7b8c1f754

52. ReactiveCocoa 3

53. RxSwift

54. Interstellar
available on Carthage
jensravens/interstellar

55. Thank you.
@JensRavens
github.com/jensravens/interstellar