Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Finding Happiness in Functional Programming
Search
Brandon Williams
October 01, 2016
Programming
0
610
Finding Happiness in Functional Programming
Video:
https://www.youtube.com/watch?v=A0VaIKK2ijM
Brandon Williams
October 01, 2016
Tweet
Share
More Decks by Brandon Williams
See All by Brandon Williams
Server-Side Swift from Scratch
mbrandonw
4
1.7k
Playground Driven Development
mbrandonw
0
320
Anything You Can Do I Can Do Better
mbrandonw
1
120
The Two Sides of Testing
mbrandonw
1
140
Other Decks in Programming
See All in Programming
Quality Gates in the Age of Agentic Coding
helmedeiros
PRO
1
130
SwiftでMCPサーバーを作ろう!
giginet
PRO
2
230
Terraform やるなら公式スタイルガイドを読もう 〜重要項目 10選〜
hiyanger
12
3k
リッチエディターを安全に開発・運用するために
unachang113
1
360
LLMは麻雀を知らなすぎるから俺が教育してやる
po3rin
3
2k
バイブスあるコーディングで ~PHP~ 便利ツールをつくるプラクティス
uzulla
1
330
SQLアンチパターン第2版 データベースプログラミングで陥りがちな失敗とその対策 / Intro to SQL Antipatterns 2nd
twada
PRO
38
11k
[DevinMeetupTokyo2025] コード書かせないDevinの使い方
takumiyoshikawa
2
270
一人でAIプロダクトを作るための工夫 〜技術選定・開発プロセス編〜 / I want AI to work harder
rkaga
7
1.7k
#QiitaBash TDDで(自分の)開発がどう変わったか
ryosukedtomita
1
350
オホーツクでコミュニティを立ち上げた理由―地方出身プログラマの挑戦 / TechRAMEN 2025 Conference
lemonade_37
1
450
それ CLI フレームワークがなくてもできるよ / Building CLI Tools Without Frameworks
orgachem
PRO
17
3.7k
Featured
See All Featured
Learning to Love Humans: Emotional Interface Design
aarron
273
40k
Building Applications with DynamoDB
mza
96
6.5k
The Psychology of Web Performance [Beyond Tellerrand 2023]
tammyeverts
49
3k
Build your cross-platform service in a week with App Engine
jlugia
231
18k
Building an army of robots
kneath
306
45k
Measuring & Analyzing Core Web Vitals
bluesmoon
8
550
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
229
22k
Keith and Marios Guide to Fast Websites
keithpitt
411
22k
Cheating the UX When There Is Nothing More to Optimize - PixelPioneers
stephaniewalter
283
13k
Docker and Python
trallard
45
3.5k
How To Stay Up To Date on Web Technology
chriscoyier
790
250k
Connecting the Dots Between Site Speed, User Experience & Your Business [WebExpo 2025]
tammyeverts
8
440
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
[email protected]