Finding Happiness in Functional Programming

Video: https://www.youtube.com/watch?v=A0VaIKK2ijM

Transcript

1. Finding Happiness in Functional Programming
3. Principles that we benefited from
4. Separation of effects from purity
5. Isolation of side-effects An expression is said to have a side-effect if its execution makes an observable change to the outside world.
6. Isolation of side-effects self.titleLabel.text = user.name
7. Isolation of side-effects func update(text: String, forLabel: UILabel) { label.text = text } update(text: user.name, forLabel: self.titleLabel)
8. Isolation of side-effects self.loginButton.enabled = !self.userTextField.text.isEmpty && !self.passwordTextField.text.isEmpty
9. Isolation of side-effects func updateLoginButtonEnabled() { self.loginButton.enabled = !self.userTextField.text.isEmpty && !self.passwordTextField.text.isEmpty } func emailChanged() { self.updateLoginButtonEnabled() } func passwordChanged() { self.updateLoginButtonEnabled() }
10. Isolation of side-effects // Pure, functional world let emailChanged: Signal<String, NoError> let passwordChanged: Signal<String, NoError> let loginButtonEnabled = combineLatest(emailChanged, passwordChanged) .map { !$0.isEmpty && !$1.isEmpty } // Side-effect world loginButtonEnabled.observeNext { [weak self] in self?.loginButtonEnabled.enabled = $0 }
11. Isolation of side-effects // Pure, functional world let emailChanged: Signal<String, NoError> let passwordChanged: Signal<String, NoError> let loginButtonEnabled = combineLatest(emailChanged, passwordChanged) .map { !$0.isEmpty && !$1.isEmpty } // Side-effect world self.loginButton.rac.enabled = loginButtonEnabled
12. Surfacing of co-effects
13. Surfacing of co-effects ????????????????
14. Surfacing of co-effects If an effect is a change to the outside world after executing an expression...
15. Surfacing of co-effects If an effect is a change to the outside world after executing an expression... ...then...
16. Surfacing of co-effects If an effect is a change to the outside world after executing an expression... ...then... ...a co-effect is the state of the world that the expression needs in order to execute.
17. Surfacing of co-effects e.g. Dependency Injection
18. Surfacing of co-effects Dependency Injection func currentUserIsCreator(ofProject project: Project) -> Bool { return User.currentUser.id == project.creator.id } currentUserIsCreator(ofProject: project) // => true or false
19. Surfacing of co-effects Dependency Injection func user(_ user: User, isCreatorOfProject: Project) -> Bool { return user.id == project.creator.id } user(User.currentUser, isCreatorOfProject: project) // => true or false
20. Surfacing of co-effects References — Colin Barrett — Functional Swift Conference 2015 — Structure and Interpretation of Swift Programs — The work of Tomas Petricek — Coeffects: A calculus of context-dependent computation — Coeffects: The next big programming challenge
21. Effect/Co-effect Duality
22. Code to the interface you wish you had, not the interface you were given. - Stephen Celis
23. An interface we were given
24. An interface we were given Storyboards — Very thick abstraction layer — Separates code from data — Constantly catching up to what UIKit can do
25. An interface we wish we had Lenses
26. An interface we wish we had Lenses struct Project { let creator: User let id: Int let name: String }
27. An interface we wish we had Lenses Project.lens.name // => Lens<Project, String>
28. An interface we wish we had Lenses Project.lens.name // => Lens<Project, String> Project.lens.name .~ "Advanced Swift" // => Project -> Project
29. An interface we wish we had Lenses Project.lens.name // => Lens<Project, String> Project.lens.name .~ "Advanced Swift" // => Project -> Project project |> Project.lens.name .~ "Advanced Swift"
30. An interface we wish we had Lenses project |> Project.lens.name .~ "Advanced Swift" |> Project.lens.creator.name .~ "Chris Eidhof"
31. An interface we wish we had UIKit Lenses
32. An interface we wish we had UIKit Lenses UIView.lens.backgroundColor // => Lens<UIView, UIColor>
33. An interface we wish we had UIKit Lenses UIView.lens.backgroundColor // => Lens<UIView, UIColor> UIView.lens.backgroundColor .~ .redColor() // => UIView -> UIView
34. An interface we wish we had UIKit Lenses UIView.lens.backgroundColor // => Lens<UIView, UIColor> UIView.lens.backgroundColor .~ .redColor() // => UIView -> UIView view |> UIView.lens.backgroundColor .~ .redColor() |> UIView.lens.layer.cornerRadius .~ 4 |> UIView.lens.layer.masksToBounds .~ true
35. An interface we wish we had UIKit Lenses func roundedStyle(cornerRadius: CGFloat) -> (UIView) -> UIView { return UIView.lens.layer.cornerRadius .~ 4 <> UIView.lens.layer.masksToBounds .~ true } view |> roundedStyle(cornerRadius: 4) |> UIView.lens.backgroundColor .~ .redColor()
36. An interface we wish we had UIKit Lenses let baseButtonStyle = roundedStyle(cornerRadius: 4) <> UIButton.lens.titleLabel.font .~ UIFont(size: 16) <> UIButton.lens.contentEdgeInsets .~ .init(topBottom: 6, leftRight: 12) let greenButtonStyle = baseButtonStyle <> UIButton.lens.backgroundColor(forState: .Normal) .~ .greenColor()
37. An interface we wish we had UIKit Lenses let bigButtonStyle = baseButtonStyle <> UIButton.lens.contentEdgeInsets %~ { .init(top: $0.top * 2, left: $0.left * 2, bottom: $0.bottom * 2, right: $0.right * 2) }
38. An interface we wish we had UIKit Lenses let baseButtonStyle = roundedStyle(cornerRadius: 4) <> UIButton.lens.titleLabel.font %~~ { _, button in button.traitCollection.verticalSizeClass == .Compact ? UIFont(size: 12) : UIFont(size: 14) } <> UIButton.lens.contentEdgeInsets .~ .init(topBottom: 6, leftRight: 12)
39. Principles that we did not benefit so much from: — D.R.Y. — S.R.P. — S.O.L.I.D. — Objects
40. The Result
41. Testing
42. Test-Driven Development
43. Test-Driven Bug Fixing
44. Playground-Driven Development
45. Screenshot testing
46. Event Tracking
47. Event Tracking
48. Accessibility
49. Love for UIKit
50. Be!er working relationship with Product Managers, Designers and Engineers
51. Finding Happiness in Functional Programming
52. Finding Happiness in Functional Programming brandon@kickstarter.com