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Finding Happiness in Functional Programming
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Brandon Williams
October 01, 2016
Programming
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600
Finding Happiness in Functional Programming
Video:
https://www.youtube.com/watch?v=A0VaIKK2ijM
Brandon Williams
October 01, 2016
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Transcript
Finding Happiness in Functional Programming
None
Principles that we benefited from
Separation of effects from purity
Isolation of side-effects An expression is said to have a
side-effect if its execution makes an observable change to the outside world.
Isolation of side-effects self.titleLabel.text = user.name
Isolation of side-effects func update(text: String, forLabel: UILabel) { label.text
= text } update(text: user.name, forLabel: self.titleLabel)
Isolation of side-effects self.loginButton.enabled = !self.userTextField.text.isEmpty && !self.passwordTextField.text.isEmpty
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() }
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 }
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
Surfacing of co-effects
Surfacing of co-effects ????????????????
Surfacing of co-effects If an effect is a change to
the outside world after executing an expression...
Surfacing of co-effects If an effect is a change to
the outside world after executing an expression... ...then...
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.
Surfacing of co-effects e.g. Dependency Injection
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
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
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
Effect/Co-effect Duality
Code to the interface you wish you had, not the
interface you were given. - Stephen Celis
An interface we were given
An interface we were given Storyboards — Very thick abstraction
layer — Separates code from data — Constantly catching up to what UIKit can do
An interface we wish we had Lenses
An interface we wish we had Lenses struct Project {
let creator: User let id: Int let name: String }
An interface we wish we had Lenses Project.lens.name // =>
Lens<Project, String>
An interface we wish we had Lenses Project.lens.name // =>
Lens<Project, String> Project.lens.name .~ "Advanced Swift" // => Project -> Project
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"
An interface we wish we had Lenses project |> Project.lens.name
.~ "Advanced Swift" |> Project.lens.creator.name .~ "Chris Eidhof"
An interface we wish we had UIKit Lenses
An interface we wish we had UIKit Lenses UIView.lens.backgroundColor //
=> Lens<UIView, UIColor>
An interface we wish we had UIKit Lenses UIView.lens.backgroundColor //
=> Lens<UIView, UIColor> UIView.lens.backgroundColor .~ .redColor() // => UIView -> UIView
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
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()
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()
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) }
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)
Principles that we did not benefit so much from: —
D.R.Y. — S.R.P. — S.O.L.I.D. — Objects
The Result
Testing
Test-Driven Development
Test-Driven Bug Fixing
Playground-Driven Development
Screenshot testing
Event Tracking
Event Tracking
Accessibility
Love for UIKit
Be!er working relationship with Product Managers, Designers and Engineers
Finding Happiness in Functional Programming
Finding Happiness in Functional Programming brandon@kickstarter.com