Who's afraid of the monad? Let's have a look at results, signals and why concurrency doesn't have to be evil.

1. Taming Asynchronous
Transforms with
Interstellar

2. let me = Person(name: "Jens Ravens", company: "nerdgeschoss")
@JensRavens
GitHub: JensRavens
jensravens.com
nerdgeschoss.de

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. Optionals
and Results

6. Optionals are a box containing
something.

7. struct Cat {
func pet() -> String {
return "purrr"
}
}
let boxContainingCat: Optional<Cat> = Cat()
let sound: String?
if let cat = boxContainingCat {
sound = cat.pet()
} else {
sound = nil
}

8. struct Cat {
func pet() -> String {
return "purrr"
}
}
let boxContainingCat: Optional<Cat> = Cat()
let sound = boxContainingCat?.pet()

9. struct Cat {
func pet() -> String {
return "purrr"
}
}
let boxContainingCat: Optional<Cat> = Cat()
let sound = boxContainingCat.map { cat in cat.pet() }

10. struct Cat {
func pet() -> String? {
return "purrr"
}
}
let boxContainingCat: Optional<Cat> = Cat()
let sound: String?? = boxContainingCat.map {
cat in cat.pet()
}

11. struct Cat {
func pet() -> String? {
return "purrr"
}
}
let boxContainingCat: Optional<Cat> = Cat()
let sound: String? = boxContainingCat.flatMap {
cat in cat.pet()
}

12. func double(i: Int) -> [Int] { return [i, 2*i] }
[1, 2, 3].map(double) // [[1,2], [2,4], [3,6]]
[1, 2, 3].flatMap(double) // [[1, 2, 2,4, 3,6]

13. Error Handling

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. enum Result<T> {
case Success(T)
case Error(ErrorType)
func map<U>(f: T -> U) -> Result<U>
func flatMap<U>(f: T -> Result<U>) -> Result<U>
}

17. func ls()-> Result<[String]>
func grep(pattern: String)(values: [String]) -> [String]
func sort(values: [String]) -> [String] { return [] }
let sorted = ls().map(grep("*.jpg")).map(sort)
ls | grep *.jpg | sort

18. Interstellar

19. ls | grep *.jpg | sort

20. class Signal<T> {
func subscribe(f: Result<T> -> Void) -> Signal<T>
func next(g: T -> Void) -> Signal<T>
func error(g: ErrorType -> Void) -> Signal<T>
func update(result: Result<T>)
func update(value: T)
func update(error: ErrorType)
}
let signal = Signal<String>()
signal.next { string in print(string) }
signal.update("Hello World")

21. pushing instead of pulling

22. But what about
Threads?

23. let threadSignal = Signal<String>()
func uppercase(string: String) -> String {
return string.uppercaseString
}
threadSignal
.ensure(Thread.background)
.map(uppercase)
.ensure(Thread.main)
.next { print($0) }

24. Extending UIKit to
support Signals.

25. extension UITextField {
public var textSignal: Signal<String>
}
let textField = UITextField()
textField.textSignal.next { string in print(string) }

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

27. real world code examples

28. func executeRequest(request: Request) -> Signal<HTTPResponse>
func getURL(response: HTTPResponse) throws -> NSURL
func upload(data: NSData)(url: NSURL, completion:
Result<String>->Void)
func createEntity(path: String, completion:
Result<Conversation>->Void)
func createConversation(avatar: UIImage) ->
Signal<Conversation> {
let signal = Signal<Conversation>()
let data = UIImageJPEGRepresentation(avatar, 0.8)!
api
.executeRequest(.GetUploadURL)
.flatMap(getURL)
.flatMap(api.upload(data))
.flatMap(createEntity)
.subscribe(signal.update)
return signal
}

29. func poll() -> Signal<[Conversation]> {
let signal = Signal<[Conversation]>()
let json = api
.executeRequest(.GetConversations)
.map { $0.json }
let conversations = json
.flatMap(Sync<Conversation>(context: context).updateObjects)
let messages = json
.flatMap(getMessages)
.flatMap(Sync<Message>(context: context).updateObjects)
conversations.merge(messages)
.flatMap(context.saveAndPipe)
.next { signal.update($0.0) }
.error { signal.update($0) }
signal.map(countUnread).next(setUnreadCount)
return signal
}

30. func poll() -> Signal<[Conversation]> {
let signal = Signal<[Conversation]>()
let json = api
.executeRequest(.GetConversations)
.map { $0.json }
let conversations = json
.flatMap(Sync<Conversation>(context: context).updateObjects)
let messages = json
.flatMap(getMessages)
.flatMap(Sync<Message>(context: context).updateObjects)
conversations.merge(messages)
.flatMap(context.saveAndPipe)
.next { signal.update($0.0) }
.error { signal.update($0) }
signal.map(countUnread).next(setUnreadCount)
return signal
}
API Request
sync conversations
sync messages
wait for both
then save
update unread
count
notify listeners

31. Warpdrive

32. • Thread.main / Thread.background
• Signal.delay(seconds: NSTimeInterval)
• Signal.wait throws
• Signal.debounce(seconds: NSTimeInterval)
Coming soon:
Holodeck UIKit Bindings

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