![ElegantFunctionalProgrammingWay
val (openerO, wineO) = (Some(Opener), Some(Wine(vintage = 1997)))
val contentsO = for {
opener <- openerO
wine <- wineO
} yield opener.open(wine)
// contentsO: Option[Contents] = Some(contentsOfWine)
// no null, no NullPointerException
5](https://image.slidesharecdn.com/whyscala-170326171039/85/Functional-Programming-in-Scala-in-a-Nutshell-Review-of-Functional-Programming-in-Scala-Ch-1-5-320.jpg)
![ElegantFunctionalProgrammingWay
val (openerO, wineO) = (Some(Opener), None)
val contentsO = for {
opener <- openerO
wine <- wineO
} yield opener.open(wine)
// contentsO: Option[Contents] = None
// no null, no NullPointerException
6](https://image.slidesharecdn.com/whyscala-170326171039/85/Functional-Programming-in-Scala-in-a-Nutshell-Review-of-Functional-Programming-in-Scala-Ch-1-6-320.jpg)
![…andViceVersa
// scala code
object Person {
val MALE = "m";
}
// java code
public class App {
public static void main(String argv[]) {
Person$ person = Person$.MODULE$;
System.out.println(person.MALE());
}
}
9](https://image.slidesharecdn.com/whyscala-170326171039/85/Functional-Programming-in-Scala-in-a-Nutshell-Review-of-Functional-Programming-in-Scala-Ch-1-9-320.jpg)
![Immutability
// value, not variable
val a = 1
a = 2 // error: reassignment to val
// list
val ints1: List[Int] = 1 :: 2 :: Nil
val ints2: List[Int] = ints1 :+ 3
println(ints1) // List(1, 2)
println(ints2) // List(1, 2, 3)
println(ints2 == 1 :: 2 :: 3 :: Nil) // true
12](https://image.slidesharecdn.com/whyscala-170326171039/85/Functional-Programming-in-Scala-in-a-Nutshell-Review-of-Functional-Programming-in-Scala-Ch-1-12-320.jpg)
Functional Programming in Scala in a Nutshell: Review of Functional Programming in Scala Ch. 1
- 2. WhyScala? 2
- 3. JavaistooVerbose // construct a empty list List<Integer> list = new ArrayList<Integer>(); list.add(1); list.add(2); list.add(3); // introduce a counting index, i for (int i = 0; i<list.size(); i++) { Integer element = list.get(i); System.out.println(element); } 3
- 4. ScalaisConcise (1 :: 2 :: 3 :: Nil).foreach(println) 4
- 5. ElegantFunctionalProgrammingWay val (openerO, wineO) = (Some(Opener), Some(Wine(vintage = 1997))) val contentsO = for { opener <- openerO wine <- wineO } yield opener.open(wine) // contentsO: Option[Contents] = Some(contentsOfWine) // no null, no NullPointerException 5
- 6. ElegantFunctionalProgrammingWay val (openerO, wineO) = (Some(Opener), None) val contentsO = for { opener <- openerO wine <- wineO } yield opener.open(wine) // contentsO: Option[Contents] = None // no null, no NullPointerException 6
- 7. ScalasupportsOOP,too // OOP polymorphism val newOpener: Opener = new NormalOpener() val oldOpener: Opener = new BrokenOpener() val wine = new Wine() println(newOpener.open(wine)) // contentsOfWine println(oldOpener.open(wine)) // Exception occurs! 7
- 8. ScalaisCompatiblewithJava Compatible with Hadoop and Spark → Official language for the bigdata community // joda time based on java import org.joda.time.DateTime, java.util.Date val jodaDt: DateTime = new DateTime(new Date()) val month = month = dt.getMonthOfYear() 8
- 9. …andViceVersa // scala code object Person { val MALE = "m"; } // java code public class App { public static void main(String argv[]) { Person$ person = Person$.MODULE$; System.out.println(person.MALE()); } } 9
- 11. ByDefinition, A function is called pure if all its inputs are declared as inputs - none of them are hidden - and likewise all its outputs are declared as outputs. 1 — Kris Jenkins 1 It is not a concrete definition but easy and intuitive. 11
- 12. Immutability // value, not variable val a = 1 a = 2 // error: reassignment to val // list val ints1: List[Int] = 1 :: 2 :: Nil val ints2: List[Int] = ints1 :+ 3 println(ints1) // List(1, 2) println(ints2) // List(1, 2, 3) println(ints2 == 1 :: 2 :: 3 :: Nil) // true 12
- 13. Immutability def fibonacci(n : Int): Int = { // while loop requires temporary varables var (a, b, i) = (0, 1, 0) while( i < n ) { val c = a + b a = b b = c i = i + 1 } return a } 13
- 14. Immutability // recursion doesn't requires temporary varables def fibonacci(n : Int): Int = n match { case 0 | 1 => n case _ => fibonacci(n - 1) + fibonacci(n - 2) } 14
- 15. SideEffect,byDefinition A function is said to have a side effect if it modifies some state outside its scope or has an observable interaction with its calling functions or the outside world. — Side effect (computer science), Wikipedia 15
- 16. SideEffect // this def has a side effect def currentProgram(guide: TVGuide, channel: Int): Program = { val schedule = guide.getSchedule(channel) schedule.programAt(new Date()) } 16
- 17. SideEffect // now it has no more side effects // and it is immutable def program(guide: TVGuide, channel: Int, date: Date): Program = { val schedule = guide.getSchedule(channel) schedule.programAt(date) } 17
- 18. Let'sStartattheBeginningAgain… A Program is functional iff it has no side effects.2 2 cf. Definition using Referential Transparency 18
- 20. SoC:SeperationOfConcerns,ByDefinition Soc is separating a computer program into distinct sections, such that each section addresses a separate concern. 20
- 21. SoC:SeperationOfConcerns,forexample · JDBC · MVC Pattern · ReactiveX 21
- 22. Testing // algebraic test: // it tests the **rule** of the startsWith method. // a and b is stateless, and startsWith has no sideEffect. property("startsWith") = forAll { (a: String, b: String) => (a+b).startsWith(a) } 22
- 23. AsynchronousProgramming val task = Task { // IO tasks ... } task.unsafePerformAsync(v => v.fold(e => e.printStackTrace(), a => println(a)) ) 23
- 24. Caution!forFP Only Consider the algorithm scale, not performance. 24
- 25. Caution!forFP val list = 1 to 10 // good list .map(a => a * a) .foldLeft(0)((sum, a) => sum + a) // bad list .foldLeft(0)((sum, a) => sum + a * a) 25
- 26. TheRulesfortheFunctionalProgramming 1. Elliminate the Side Effects 2. Don't use var keyword 3. Don't use new keyword 4. Use Unit type extremely carefully 5. Use case class 6. Define equals 26
- 27. FAQ Q.Shouldilearnhaskell? A. 필수는 아니다. 단, 더 나아가기 위해 Haskell이 도움 이 될 수 있다. 대부분의 Functional Programming 문 서는 Haskell을 위주로 설명돼있다. 27
- 28. FAQ Q.PiS A. 분량도 많고, 무엇보다 함수형 프로그래밍에 초점이 맞춰진 책이 아니어서 추천하지 않는다. 28
- 29. ChapterstoProceed inFunctionalProgramminginScalaTextbook 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13 29
- 30. Practices 30
- 31. PrintingStream Write a program that prints the ints from 1 to 100. 1 2 … 100 31
- 32. FizzBuzz Write a program that prints the ints from 1 to 100. But: - for multiples of three, print Fizz - for multiples of five, print Buzz - for multiples of both three and five, print FizzBuzz 32
- 34. FizzBuzzinaRow Write a fizzbuzz program that combines the result with comma. 1, 2, Fizz, 4, Buzz, …, 98, Fizz, Buzz 34
- 35. OddNumber&to-200FizzBuzz Write a fizzbuzz-in-a-row program with the odd number stream from 1 to 199 . 1, Fizz, Buzz, …, 193, FizzBuzz, 197, 199 35
- 37. Grammars · 스칼라 학교! · 스칼라 공식 도큐먼트 입문 · Effective Scala by Twitter · Effective Scala by Heejong Lee · Hacker Rank for Tutorials · Exercism 37
- 38. WhatisFunctionalProgramming? · 함수형 프로그래밍이란 무엇인가? · 어떤 프로그래밍 언어들이 함수형인가? 38
- 39. Textbooks&References · ! 스칼라로 배우는 함수형 프로그래밍 · Functional Programming Principles in Scala on Coursera · Big Data Analysis with Scala and Spark on Coursera · Scala Excercises 39
- 40. PopularScalaLibraries · ! Scalaz: Scala library for functional programming · Cats: Lightweight, modular, and extensible library for functional programming · Monix: Asynchronous Programming for Scala · Circe: A JSON library for Scala powered by Cats 40
- 41. Haskell · Eta Programming Language, Haskell on the JVM · (가장 쉬운) 하스켈 책 : 느긋하지만 우아하고 세련된 함수형 언어 41
- 42. Resources · Scastie, an interactive playground for Scala 42