This document discusses functional programming concepts like immutable data, functions as first-class citizens, and mapping and flatMapping functions. It shows how to define Functor and Monad types to represent immutable data that can be transformed by functions in a predictable way. This allows modeling operations like changing a value or getting its length in a functional style while maintaining immutable data.

1. Ra c
) /
ED D
(-) / ) -

2. G I ED D

3. E
var number = 100
mysteryJob()
print(number)
let number = 100
mysteryJob()
print(number)

4. D DI
var number = 100
mysteryJob()
print(number)
// ?
let number = 100
mysteryJob()
print(number)
// 100
mutable immutable

5. F
var condition: Bool = true
if condition {
// true
} else {
// false
}
let condition: Bool = true
// case true
mutable immutable

6. F
var condition: Bool = true
var condition2: Bool = false
if condition {
if condition2 {
// true && true
} else {
// true && false
}
} else {
if condition2 {
// false && true
} else {
// false && false
}
}
let condition: Bool = true
let condition2: Bool = false
// case true && false
mutable immutable

7. F
var condition: Bool = true
var condition2: Bool = false
var condition3: Bool = false
if condition {
if condition2 {
if condition3 {
// true && true && true
} else {
// true && true && false
}
} else {
if condition3 {
// true && false && true
} else {
// true && false && false
}
}
} else {
if condition2 {
if condition3 {
// false && true && true
} else {
// false && true && false
}
} else {
if condition3 {
// false && false && true
} else {
// false && false && false
}
}
}
let condition: Bool = true
let condition2: Bool = false
let condition2: Bool = false
// case true && false && false
mutable immutable

8. / D
Data
Program Program Program Program
Data
Program Program Program Program
mutable immutable

9. D C
mutable immutable
struct Hero {
var name : String
var nickname: String
}
var hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
print(hero)
//Hero(name: "Steve Rogers",
nickname: "Captain America")
hero.nickname = "First Avenger"
print(hero)
//Hero(name: "Steve Rogers",
nickname: "First Avengers")
struct Hero {
var name : String
var nickname: String
}
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
print(hero)
//Hero(name: "Steve Rogers",
nickname: "Captain America")
let captain = Hero(name: hero.name,
nickname: "First Avenger")
print(hero)
//Hero(name: "Steve Rogers",
nickname: "Captain America")
print(captain)
//Hero(name: "Steve Rogers",
nickname: "First Avengers")

10. ED D
1. Predictable
2. Testability
3. Thread-Safe
Maintainable
}
4. Unfamiliar
5. Memory wasting
6. Low performance
( in some case )

11. ED FC ED D
Maintenance
Performance
vs

12. ECF EC EC

13. Data
feature

14. AI
struct Hero {
var name: String
var nickname: String
}
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
var captain = hero
captain.nickname = "First Avenger" Copy On Write

15. HD C
protocol Mappable {
func map<U>(_ f: (Self) -> U) -> U
}
extension Mappable {
func map<U>(_ f: (Self) -> U) -> U {
return f(self)
}
}
extension Hero: Mappable { }
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
let captain = hero.map { hero -> Hero in
var h = hero
h.nickname = "First Avenger"
return h
}

16. DD DD
extension Hero {
func get<Value>(_ kp: KeyPath<Hero, Value>) -> Value {
return self[keyPath: kp]
}
func set<Value>(_ kp: WritableKeyPath<Hero, Value>,
_ v: Value) -> Hero {
var h = self
h[keyPath: kp] = v
return h
}
}
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
hero.get(.nickname)
//Captain America
let captain = hero.set(.nickname, "First Avenger")

17. C
struct Lens<Whole, Part> {
let get: (Whole) -> Part
let set: (Whole, Part) -> Whole
}
let heroNickNameLens: Lens<Hero, String> = Lens(
get: { $0.nickname },
set: {
var h = $0
h.nickname = $1
return h
}
)
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
let captain = heroNickNameLens.set(hero, "First Avenger")

18. C
protocol Lensable {
static func lens<Part>(_ wkp: WritableKeyPath<Self, Part>) -> Lens<Self, Part>
}
extension Lensable {
static func lens<Part>(_ wkp: WritableKeyPath<Self, Part>) -> Lens<Self, Part> {
return Lens(
get: { whole in whole[keyPath: wkp] },
set: { whole, part in
var mutableWhole = whole
mutableWhole[keyPath: wkp] = part
return mutableWhole
}
)
}
}
extension Hero: Lensable {}
let hero = Hero(name: "Steve Rogers",
nickname: "Captain America")
let captain = Hero.lens(.nickname).set(hero, "First Avenger")

19. E D AD C
http://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/poptics.pdf
https://github.com/hablapps/DontFearTheProfunctorOptics

20. feature
Data

21. E D
func valueChanger<T, U>(value: T, _ f: (T) -> U) -> U {
return f(value)
}
let name = "Original"
// Original
let changedName = valueChanger(value: name) { "($0) Changed" }
// Original Changed

22. E D
class Functor<T> {
let value: T
init(_ v: T) {
value = v
}
func map<U>(_ f: (T) -> U) -> Functor<U> {
let u = f(value)
return Functor<U>(u)
}
}

23. E D
let name = "Original" // Original
let changedName = Functor(name).map { "($0) Changed" }.value
// Original Changed
let changedNameLength = Functor(name) // Functor<String>
.map { "($0) Changed" } // Functor<String>
.map { $0.count } // Functor<Int>
.map { $0 * $0 } // Functor<Int>
.value // Int
// 256

24. E D
func stringLength(_ s: String) -> Functor<Int> {
return Functor(s).map { $0.count }
}
let name = "Original" // Original
let changedName = Functor(name).map { "($0) Changed" }.value
// Original Changed
let changedNameLength = Functor(name) // Functor<String>
.map { "($0) Changed" } // Functor<String>
.map (stringLength) // Functor<Functor<Int>>
.map { $0 * $0 }
.value

25. E D
func stringLength(_ s: String) -> Functor<Int> {
return Functor(s).map { $0.count }
}
let name = "Original" // Original
let changedName = Functor(name).map { "($0) Changed" }.value
// Original Changed
let changedNameLength = Functor(name) // Functor<String>
.map { "($0) Changed" } // Functor<String>
.map (stringLength) // Functor<Functor<Int>>
.map { $0 * $0 }
.value
Functor<Functor<Int>> 의 중첩된 것을 단일(Mono)하게 만들어야 함.

26. class Monad<T>: Functor<T> {
override func map<U>(_ f: (T) -> U) -> Monad<U> {
let cu = super.map(f)
return Monad<U>(cu.value)
}
func flatMap<U>(_ f: (T) -> Functor<U>) -> Monad<U> {
let fu = f(value)
return Monad<U>(fu.value)
}
}

27. func stringLength(_ s: String) -> Functor<Int> {
return Functor(s).map { $0.count }
}
let name = "Original" // Original
let changedName = Monad(name).map { "($0) Changed" }.value
// Original Changed
let changedNameLength = Monad(name) // Monad<String>
.map { "($0) Changed" } // Monad<String>
.flatMap (stringLength) // Monad<Int>
.map { $0 * $0 } // Monad<Int>
.value // Int
//256

28. E I
Immutable data 는 변하지 않는 값
f
g = f - ) -
b df - )
-) ).-
e f P
map / flatMap
Data
get / set
유지보수하기 좋다