Introduction to Functional Reactive

Programming

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About me

Eliasz SawickiBlog: www.eliaszsawicki.comTwitter: @EliSawic

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Agenda• What is functional reactive programming?

• Working with streams

• ReactiveSwift - Thinking in signals

• Example

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Functional Reactive Programming

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WikipediaFunctional reactive programming (FRP) is a programming paradigm for reactive programming (asynchronous dataflow programming) using the building blocks of functional programming (e.g. map, reduce, filter).

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Reactive Programming

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Functional Programming

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Blocks

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Imperative vs

Declarative

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Imperative

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Imperativelet array = [0, 1, 2, 3, 4, 5]var evenNumbers = [Int]()for element in array { if element % 2 == 0 { evenNumbers.append(element) }}

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Declarative

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Declarativelet array = [0, 1, 2, 3, 4, 5]let evenNumbers = array.filter { $0 % 2 == 0 }

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Working with streams

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Stream

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Manipulating streams

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Map

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Filter

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Aggregating

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Manipulating multiple streams

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Combine latest

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Merge

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Chaining streams

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www.rxmarbles.com

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ReactiveSwift

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Thinking in Signals

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What is a signal?

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This screen is a signal

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Represents events over time

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Observing does not trigger side effects

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No random access to events

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Observe

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If you don't listen, it's gone

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What is event?

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Eventstruct Idea { var content: String var quality: Quality}

enum Quality { case Great case Average case Worst}

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Non-Terminating• Next

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Terminating

• Completed

• Failed

• Interrupted (Reactive Cocoa)

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Presentationlet (presentation, presentationObserver) = Signal<Idea, NoError>.pipe()

let content = "This presentation is a signal"let idea = Idea(content: content, quality: .Great)

presentationObserver.send(value: idea)presentationObserver.sendCompleted()

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Observingpresentation.observeValues { idea in remember(idea: idea)}presentation.observeCompleted { print("Time for a break")}

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Only great ideaslet greatIdeas = presentation.filter { idea in idea.quality == .Great}greatIdeas.observeValues { greatIdea in remember(idea: greatIdea)}

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Positive listenerlet greatPresentation = presentation.map { idea -> Idea in var greatIdea = idea greatIdea.quality = .Great return greatIdea}

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Signal producer

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Represents a tasks

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Possible side effects

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Does not start it's work if not asked

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Run presentationfunc runPresentation() -> SignalProducer<Idea, NoError> { return SignalProducer { observer, _ in observer.send(value: idea1) observer.send(value: idea2) ... observer.sendCompleted() }}

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Work with presentationrunPresentation().startWithValues { idea in print(idea)}

runPresentation().startWithSignal { (signal, _) in signal.observeValues({ idea in print(idea) })

signal.observeCompleted { print("Finally...") }}

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Cold vs Hot

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Properties

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Mutable Propertylet firstSlide = Slide(number: 1)let slide = MutableProperty<Slide>(firstSlide)slide.producer.startWithValues { (text) in print(text)}slide.value = Slide(number: 2)

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Bindings

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Binding examplelet slideNumber = MutableProperty<Int>(0)let (signal, _) = Signal<Slide, NoError>.pipe()

slideNumber <~ signal.map { return $0.number }

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Binding examplelet (signal, _) = Signal<Slide, NoError>.pipe()

label.reactive.text <~ signal.map { return "Slide: \($0.number)" }

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Schedulers

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Know where you aresignal.observe(on: QueueScheduler.main).observeValues { idea in print("Performing UI updates")}

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Memory Management

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Disposables

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Free your memorylet disposable = signal.observeValues { value in ...}

disposable.dispose()

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Release your producerslet disposable = producer.startWithValues { value in ...}

disposable.dispose()

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Example

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How does it work?

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Is name valid?let isValidNameSignal = nameSignal.map { (name) -> Bool in return name.characters.count > 2}

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Is surname valid?let isValidSurnameSignal = surnameSignal.map { (surname) -> Bool in return surname.characters.count > 2}

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Is mail valid?let isValidMailSignal = mailSignal.map { (mail) -> Bool in let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}" let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx) return emailTest.evaluateWithObject(mail)}

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Combine Latestlet formDataSignal = combineLatest( isValidNameSignal, isValidSurnameSignal, isValidMailSignal)

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Is form valid?let isValidFormSignal = formDataSignal.map { (isValidName, isValidSurname, isValidMail) -> Bool in return isValidMail && isValidSurname && isValidMail}

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Update the stateisValidFormSignal.observeValues { isValid in updateButtonWith(state: isValid)}

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Bindinglet isValidForm = MutableProperty<Bool>(false)

isValidForm <~ isFormValidSignal

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Conclusion

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Thank you for your attention!sendCompleted()

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