TDC2018SP | Trilha Prog Funcional - Programacao funcional na pratica com Swift

Programação Funcional na
Prática com Swift
Rodrigo Amorim Ruiz
Vikki (vikki.ai)

Porque Swift
• Passagem por valor
• Tipagem estática + inferência
• Optional
• Lambda e outras construções de FP
• Enum

VS
Programação Orientada a Objetos
Programação Funcional
Comparação

Considerações
• Swift vs Cocoa
• Questão de estilo
• OO / Procedural / Imperativo
• Técnicas de FP em OO
• Performance
• Leitura vs Escrita
• Melhor ferramenta para cada problema

Programação Funcional Programação Orientada a ObjetosVS

TDC2018SP | Trilha Prog Funcional - Programacao funcional na pratica com Swift

Class vs Struct
// OO
func customPrint(person: Person) {
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(10), execute: {
print("After 10 seconds: (person.name)")
})
}
class Person {
var name: String
init(name: String) {
self.name = name
}
}
let p = Person(name: "Rodrigo")
customPrint(person: p)
p.name = "Thomas"
print(p.name)

Class vs Struct
// FP
func customPrint(person: Person) {
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(10), execute: {
print("After 10 seconds: (person.name)")
})
}
struct Person {
var name: String
}
let p = Person(name: "Rodrigo")
customPrint(person: p)
p.name = "Thomas"
print(p.name)

Map
// OO
var values = [Double]()
for step in steps {
values.append(sin(Double(step) / 10))
}
print(values)
// FP
let values = steps.map({ sin(Double($0) / 10) })
print(values)
let steps = (1...100)

Filter
// OO
var partyFriends = [String]()
for friend in friends {
if friend.age >= 18 && friend.age <= 40 {
partyFriends.append(friend.name)
}
}
print(partyFriends)
// FP
let partyFriends = friends
.filter({ $0.age >= 18 && $0.age <= 40 })
.map({ $0.name })
print(partyFriends)
let friends = [
(name: "Pedro", age: 12),
(name: "Maria", age: 18),
(name: "João", age: 21),
(name: "Regina", age: 55)
]

Reduce
// OO
var totalMoney = 0
for money in moneyPile {
totalMoney += money
}
var text = ""
for character in characters {
text += character
}
print(totalMoney)
print(text)
// FP
let totalMoney = moneyPile.reduce(0, +)
let text = characters.reduce("", +)
print(totalMoney)
print(text)
let moneyPile = [10, 20, 15, 30]
let characters = ["a", "b", "c", "d"]

Count Words
// Procedural
let content = readFile()
let words = content.split(separator: " ")
var tally = [String: Int]()
for word in words {
let lowerCaseWord = word.lowercased()
tally[lowerCaseWord] = (tally[lowerCaseWord] ?? 0) + 1
}
var tallyAsArray = [(word: String, count: Int)]()
for (key, value) in tally {
tallyAsArray.append((word: key, count: value))
}
tallyAsArray.sort(by: { $0.count > $1.count })
var top10 = [(word: String, count: Int)]()
for i in (0..<10) {
top10.append(tallyAsArray[i])
}
for value in top10 {
print("(value.word) - (value.count)")
}

Count Words
// OO
class WordCounter {
func printTop10() {
readFileToContent()
splitContentIntoWords()
createTally()
sortTally()
getTop10Words()
printTop10()
}
private var content = ""
private var words = [String.SubSequence]()
private var tally = [String: Int]()
private var tallyAsArray = [(word: String, count: Int)]()
private var top10 = [(word: String, count: Int)]()
private func readFileToContent() { … }
private func splitContentIntoWords() { … }
private func createTally() { … }
private func sortTally() { … }
private func getTop10Words() { … }
private func printTop10Words() { … }
}
let w = WordCounter()
w.printTop10()

Count Words
// FP
let output = readFile()
.split(separator: " ")
.map({ $0.lowercased() })
.reduce([String: Int](), { (tally, lowerCaseWord) in
return tally.merging(
[lowerCaseWord: (tally[lowerCaseWord] ?? 0) + 1],
uniquingKeysWith: { $1 }
)
})
.sorted(by: { $0.value > $1.value })
.prefix(10)
.map({ "($0.key) - ($0.value)" })
.joined(separator: "n")
print(output)

Requests (OO)
let party = CreateParty(delegate: CreatePartyDelegate())
party.create()
class CreateParty: SendAPIRequestDelegate {
init(delegate: CreatePartyDelegate) {
self.delegate = delegate
self.friendsRequest = SendAPIRequest(url: "https://api.com/friends", delegate: self)
self.placeRequest = SendAPIRequest(url: "https://api.com/place", delegate: self)
}
func create() {
self.friendsRequest.request()
self.placeRequest.request()
}
...
}

Requests (OO)
...
// MARK: - SendAPIRequestDelegate
func success(request: SendAPIRequest, json: JSON) {
if request === self.friendsRequest {
self.friends = json.array!.map(toString)
friendsReady = true
tryToCreatePartyData()
}
if request === self.placeRequest {
self.place = json.string!
placeReady = true
}
}
func failure(request: SendAPIRequest, error: APIRequestError) {
if request === self.friendsRequest {
friendsReady = true
}
if request === self.placeRequest {
placeReady = true
}
}
...
}

Requests (OO)
...
// MARK: - Private
private var friendsRequest: SendAPIRequest!
private var placeRequest: SendAPIRequest!
private var friendsReady = false
private var placeReady = false
private var friends: [String]?
private var place: String?
private let delegate: CreatePartyDelegate
private var party: Party?
private func tryToCreatePartyData() {
if !self.friendsReady || !self.placeReady {
return
}
if let friends = self.friends, let place = self.place {
self.party = Party(friends: friends, place: place)
} else {
self.party = nil
}
callDelegateWithPartyData()
}
...
}

Requests (OO)
class CreatePartyDelegate {
func printNoParty() {
print("There will be no party.")
}
func printParty(party: Party) {
print("Go party!!!")
print("Place: (party.place)")
print("Friends:")
for friend in party.friends {
print(friend)
}
}
}
...
// MARK: - Private
...
private func callDelegateWithPartyData() {
guard let party = self.party else {
delegate.printNoParty()
return
}
delegate.printParty(party: party)
}
}

Requests (FP1)
let friendsObservable = sendAPIRequest(url: "https://api.com/friends")
.map(getSuccess >>> map(toArray >>> map(toString)))
let placeObservable = sendAPIRequest(url: "https://api.com/place")
.map(getSuccess >>> map(toString))
let partyObservable = Observable
.zip(friendsObservable, placeObservable)
.map(mergeOptionals >>> map(applyTuple(Party.init)))
let outputObservable = partyObservable.map(
map({
"Go party!!!n"
+ "Place: ($0.place)n"
+ "Friends:n"
+ $0.friends.joined(separator: "n")
})
>>> defaultTo("There will be no party.")
)
_ = outputObservable.subscribe(onNext: { print($0) })

Requests (FP2)
(
"https://api.com/friends",
"https://api.com/place"
)
>>> both(sendAPIRequest >>> map(getSuccess))
>>> first(map(map(toArray >>> map(toString))))
>>> second(map(map(toString)))
>>> applyTuple(Observable.zip)
>>> map(mergeOptionals >>> map(applyTuple(Party.init)))
>>> map(
map({
"Go party!!!n"
+ "Friends:n"
})
)
>>> subscribe(onNext: { print($0) })

Requests (FP2’)
let mapFriends: (Observable<JSON?>) -> Observable<[String]?> = map(map(toArray >>> map(toString)))
let mapPlace: (Observable<JSON?>) -> Observable<String?> = map(map(toString))
let requests = both(sendAPIRequest >>> map(getSuccess))
>>> first(mapFriends)
>>> second(mapPlace)
let createParty: ((Observable<[String]?>, Observable<String?>)) -> Observable<Party?> =
applyTuple(Observable.zip)
>>> map(mergeOptionals >>> map(applyTuple(Party.init)))
let toOutputString: (Observable<Party?>) -> Observable<String> = map(
map({
"Go party!!!n"
+ "Friends:n"
})
)
let requestStringsToOutput = requests
>>> createParty
>>> toOutputString
_ = requestStringsToOutput((
"https://api.com/friends",
"https://api.com/place"
)).subscribe(onNext: { print($0) })

Conceitos Utilizados
• Dados x Comportamento
• Imperativo vs Declarativo
• Funções puras
• Imutabilidade
• Funções de alta ordem
• Functors, Applicatives e Monads
• Maybe (Optional)
• Array
• Result
• Promise / Observable

Haskell vs. Ada vs. C++ vs. Awk vs. ...
An Experiment in Software Prototyping
Productivity∗
Paul Hudak Mark P. Jones
Yale University
Department of Computer Science
New Haven, CT 06518 {hudak-paul,jones-mark}@cs.yale.edu
July 4, 1994

https://www.linkedin.com/in/rodrigoaruiz/

TDC2018SP | Trilha Prog Funcional - Programacao funcional na pratica com Swift

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