More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (20)
Similar to Scala: functional programming for the imperative mind
Similar to Scala: functional programming for the imperative mind (20)
More from Sander Mak (@Sander_Mak)
More from Sander Mak (@Sander_Mak) (20)
Recently uploaded
Recently uploaded (20)
Scala: functional programming for the imperative mind
- 1. Scala Functional programming for the imperative mind
- 2. Scala Functional programming for the imperative mind ‘of the nature of or expressing a command; commanding.’ - imperative. (n.d.). Dictionary.com
- 3. Scala ‘imperative Functional programmingisfor the imperative mind programming a programming paradigm that describes computation in terms of statements that change a program state.’ - Imperative programming Wikipedia.com
- 4. Outline • Introduction • Functional programming • Scala features • Java to Scala in three steps • Scala community • Wrap up
- 5. Roots • Created by Martin Odersky • Supported by EPFL Switzerland
- 6. What is Scala? A programming language ... • Runs on JVM (and .Net) • Statically typed • Object Oriented • Functional • From scripting to enterprise apps
- 7. Scalable language • Scalable language constructs: • Composition ‘in the small’ • Composition ‘in the large’ • Java interoperability • Performance on par with Java
- 8. Scalable language • Scalable language constructs: • Composition ‘in the small’ • Composition ‘in the large’ • Java interoperability • Performance on par with Java Fuses functional and object oriented paradigms
- 9. What is Functional Programming
- 10. Functional programming • Focus on functions, not state fx=x+1 • Functions are values vs. • Recursion, not loops x=x+1 • Immutability (‘referential transparency’) • Schools of thought: pure and impure (‘pragmatic’)
- 11. Functional programming • Focus on functions, not state fx=x+1 • Functions are values vs. • Recursion, not loops x=x+1 • Immutability (‘referential transparency’) • Schools of thought: pure and impure (‘pragmatic’)
- 12. Functional programming • Focus on functions, not state • Functions are values f g x = g(x) • Recursion, not loops • Immutability (‘referential transparency’) • Schools of thought: pure and impure (‘pragmatic’)
- 13. Functional programming • Focus on functions, not state f0=0 fx= • Functions are values f (x - 1) vs. • Recursion, not loops for(i=x; i>0 ; i--) { • Immutability (‘referential transparency’)x--; } • Schools of thought: pure and impure (‘pragmatic’)
- 14. Functional programming • Focus on functions, not state • Functions are values • Recursion, not loops • Immutability (‘referential transparency’) • Schools of thought: pure and impure (‘pragmatic’)
- 15. Functional programming Why should I care about FP? • Concurrency: FP ‘killer app’ • Higher order functions: expressiveness boost • Type-system: when present, often superior • It is coming to a language near you (C#, Java 8?)
- 16. FP in Scala • First-class functions: functions are objects with pleasing syntax • Immutability • Algebraic data-types and pattern matching • Parametric polymorphism (e.g. generics)
- 17. What are Scala’s Features
- 18. Scala is like Java... (Generic) classes: class Foo[T], or: class Foo[+T] public class Foo<T> Methods: def m(s : String) : Unit = .. public void m(String s) {..} Bean properties: private Foo foo; Real properties: getFoo() {..}, setFoo(..) {..} var foo: Foo Fully interoperable with existing Java Mature, large amount of proven libraries code Class/Interface distinction, single Abstract classes, traits (restricted inheritance. multiple inheritance)
- 19. Pure object orientation No primitive types:
- 20. Pure object orientation No primitive types:
- 21. Pure object orientation Every operation is a method call: 1+3 1.+(3)
- 22. Pure object orientation Every operation is a method call: 1+3 1.+(3) Console.println(“hi”) Console println “hi”
- 23. Pure object orientation Every operation is a method call: 1+3 1.+(3) Console.println(“hi”) Console println “hi” Since operators are methods, operator overloading is trivial.
- 24. Pure object orientation Every operation is a method call: 1+3 1.+(3) Console.println(“hi”) Console println “hi”
- 25. Pure object orientation Every operation is a method call: 1+3 1.+(3) Console.println(“hi”) Console println “hi”
- 26. Pure object orientation No static members, but singleton objects:
- 27. Type inference • Types may be omitted in declarations • Does not mean there is no type! • Inference is local only • Var/val: mutable vs. immutable
- 28. Type inference
- 29. Everything is an expression
- 30. Everything is an expression
- 31. Everything is an expression
- 32. Everything is an expression
- 33. Functional objects • Functions are first-class values • Function literals:
- 34. Functional objects • Functions are first-class values • Function literals: (x: Int) => x * 2
- 35. Functional objects • Functions are first-class values • Function literals: (x: Int) => x * 2 val double = (x: Int) => x * 2
- 36. Functional objects • Functions are first-class values • Function literals: (x: Int) => x * 2 val double = (x: Int) => x * 2 double(2) == 4 What is the type of double?
- 37. Functional types val double = (x: Int) => x * 2 has type (Int) => Int
- 38. Functional types val double = (x: Int) => x * 2 has type (Int) => Int Function1[Int,Int]
- 39. Passing functions Since functions are values, we can pass them around:
- 40. Passing functions But we can do this with anonymous classes...
- 41. Passing functions But we can do this with anonymous classes...
- 42. Passing functions But we can do this with anonymous classes...
- 43. Passing functions But we can do this with anonymous classes... Well, sort of... but: • You need explicit interfaces (no function types) • Verbose • Doesn’t scale (syntactically and semantically) • No true closures:
- 44. Passing functions But we can do this with anonymous classes... Well, sort of... but: • You need explicit interfaces (no function types) • Verbose • Doesn’t scale (syntactically and semantically) • No true closures:
- 45. Traits • Compare trait with abstract class • No interfaces, but: completely abstract traits • Can mixin multiple traits, statically and dynamically
- 46. Traits as rich interfaces Java interfaces have two consumers with conflicting interests: 1) Implementors 2) Users
- 47. Traits as rich interfaces Java interfaces have two consumers with conflicting interests: 1) Implementors 2) Users
- 48. Traits as stackable modifications • Situation: IntQueue interface (abstract trait), IntQueueImpl implementation • We want to add logging and filtering to any IntQueue implementation
- 49. Traits as stackable modifications • Situation: IntQueue interface (abstract trait), IntQueueImpl implementation • We want to add logging and filtering to any IntQueue implementation
- 50. Traits as stackable modifications • Situation: IntQueue interface (abstract trait), IntQueueImpl implementation • We want to add logging and filtering to any IntQueue implementation
- 51. Pattern matching
- 52. Pattern matching
- 53. Pattern matching Yes, it prints 9
- 54. Pattern matching • No more instanceof/typecasts • No more visitor pattern
- 55. Pattern matching • No more instanceof/typecasts • No more visitor pattern No more NullPointerException:
- 56. Pattern matching & XML • Scala has XML literals, can be matched • Other literals can be matched as well
- 57. Language feature or Library Support
- 58. Actors • Message-based concurrency • Actors exchange immutable messages • Extract them by pattern matching
- 59. Actors • Message-based concurrency • Actors exchange immutable messages • Extract them by pattern matching Looks like language feature, but is a library
- 60. Other library features • Enums • Map ‘syntax’ • Events • Using ‘keyword’ (e.g. Java 7 ‘automatic resource management.’) • Virtually all other Project Coin proposals
- 61. Other library features • Enums • Map ‘syntax’ • Events • Using ‘keyword’ (e.g. Java 7 ‘automatic resource management.’) • Virtually all other Project Coin proposals
- 62. Other library features • Enums • Map ‘syntax’ • Events • Using ‘keyword’ (e.g. Java 7 ‘automatic resource management.’) • Virtually all other Project Coin proposals
- 63. Other library features • Enums • Map ‘syntax’ • Events • Using ‘keyword’ (e.g. Java 7 ‘automatic resource management.’) • Virtually all other Project Coin proposals Lesson: choose language core wisely, all else will follow...
- 64. Lift webframework In own words: ✓Seaside's highly granular sessions and security ✓Rails fast flash-to-bang ✓Django's quot;more than just CRUD is includedquot; ✓Wicket's designer-friendly templating style • Heavy use of actors for async features • Integrated O/R mapping (surprisingly little boilerplate code)
- 65. From Java to Scala In Three steps
- 66. Requirements • Person entity with age property • Method to separate minors and adults • Input: List[Person] • Output: list of minors, list of adults • One pass over input
- 67. Requirements • Person entity with age property • Method to separate minors and adults • Input: List[Person] • Output: list of minors, list of adults • One pass over input
- 68. What happens in the Scala Community
- 69. Scala progression • Current version: 2.7.4 • Version 2.8 beta coming up: • Package objects • Named and default parameters • Many library improvements
- 70. Tool support • Major IDEs (Eclipse, IntelliJ, NetBeans) supported • Maven support • Scaladoc • SBaz package manager
- 71. Wrapping up with Concluding Remarks
- 72. Scala hitting mainstream? Reports of first switchers Twitter, SAP, LinkedIn, Sony Pictures
- 73. Scala hitting mainstream? Reports of first switchers Twitter, SAP, LinkedIn, Sony Pictures April 2009: top-30 of TIOBE index
- 74. Scala hitting mainstream? Reports of first switchers Twitter, SAP, LinkedIn, Sony Pictures April 2009: top-30 of TIOBE index Lots of books appearing
- 75. Scala hitting mainstream? “If I were to pick a language today other than Java, it would be Scala” James Gosling, ‘Father of Java’
- 76. Scala hitting mainstream? “If Java programmers want to use features that aren't present in the language, I think they're probably best off using another language that targets the JVM, such a Scala and Groovy.” Joshua Bloch Author of ‘Effective Java’
- 77. Pro’s and cons • Complexity • Java interoperability • Java -> Scala • Hides accidental complexity harder than Scala -> Java • Expressiveness • Type-system may • Uniform, extensible be intimidating language
- 78. Conclusion • Scala feels like ‘cleaned up Java on stereoids’ • Small core (takes some time to see it as such) provides broad options • Type inference brings ‘dynamic language’ feel • Adoptation growing because of: • Java interoperability • Growing discontent with Java
- 79. Conclusion • Scala feels like ‘cleaned up Java on stereoids’ • Small core (takes some time to see it as such) provides broad options • Type inference brings ‘dynamic language’ feel • Adoptation growing because of: • Java interoperability • Growing discontent with Java Scala provides deep features, but at the same time helps getting things done.
- 80. More information http://www.scala-lang.org http://liftweb.net Article Java Magazine 1/2009
- 81. Questions?
Editor's Notes
- Intro, gaan het hebben over Scala Wellicht al eens gehoord over FP, lijkt groeiende interesse wat is imperatief? Ook wel procedureel, met state, het is wat we in Java eigenlijk doen.
- Intro, gaan het hebben over Scala Wellicht al eens gehoord over FP, lijkt groeiende interesse wat is imperatief? Ook wel procedureel, met state, het is wat we in Java eigenlijk doen.
- Intro, gaan het hebben over Scala Wellicht al eens gehoord over FP, lijkt groeiende interesse wat is imperatief? Ook wel procedureel, met state, het is wat we in Java eigenlijk doen.
- Odersky: co-designer generics, original author javac. Wellicht had hier oracle logo moeten staan :)
- *Voordelen JVM (enorm veel tijd in optimalisatie, platform agnostisch etc.), ook wat nadelen (niet echt ingericht op FP constructies). * OO, maar dan ook puur, en met extra functionaliteit * Scripting: REPL shell
- Scala redelijk uniek in samenvoegen OO+FP OCaml en F# zijn toch meer FP met een OO systeem er aan geplakt.
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Recursie niet alleen in functies, ook in data (bomen, lijsten)
- Nieuwe paradigma’s hebben killer-app nodig OO had GUIs, bij FP concurrency? Typesysteem: niet noodzakelijk voor FP, traditioneel wel focus
- Zonder diep in te gaan, voor we features gaan bekijken, dit is hoe Scala FP bevat.
- *default modifier is public *Type after identifier, type Unit == void *zowel Scala->Java als Java->Scala interop. Dus, elkaars classes instantieren overerven etc. *Abstract class ipv interfaces
- Extenden van Java class (extends ook voor interfaces) Type Unit -> void in Java hashCode -> hashCode() , haakjes weglaten. Soort van autoboxing, maar beter
- * + is methode naam, kan je zelf op een class implementeren * Leestekens legale identifiers in Scala * Operator notatie ook te gebruiken met ‘normale’ methode namen * In Java discussie: operator overloadig BigInts (en wat voor matrix etc.)? Scala: just do it.
- * + is methode naam, kan je zelf op een class implementeren * Leestekens legale identifiers in Scala * Operator notatie ook te gebruiken met ‘normale’ methode namen * In Java discussie: operator overloadig BigInts (en wat voor matrix etc.)? Scala: just do it.
- * + is methode naam, kan je zelf op een class implementeren * Leestekens legale identifiers in Scala * Operator notatie ook te gebruiken met ‘normale’ methode namen * In Java discussie: operator overloadig BigInts (en wat voor matrix etc.)? Scala: just do it.
- * + is methode naam, kan je zelf op een class implementeren * Leestekens legale identifiers in Scala * Operator notatie ook te gebruiken met ‘normale’ methode namen * In Java discussie: operator overloadig BigInts (en wat voor matrix etc.)? Scala: just do it.
- * + is methode naam, kan je zelf op een class implementeren * Leestekens legale identifiers in Scala * Operator notatie ook te gebruiken met ‘normale’ methode namen * In Java discussie: operator overloadig BigInts (en wat voor matrix etc.)? Scala: just do it.
- *Java statics niet echt OO. Scala: Classes->te instantieren, singleton objects->één instantie *Zelfde naam: companions -> toegang tot private members *haakjes mogen weg bij methode aanroep zonder params; puntkomma’s ook optioneel! *main methode op object Main, entrypoint applicatie
- * Vorige slide goed opgelet: geen return type!
- * Zijn natuurlijk allemaal op ISKA over closures geweest, maar toch een opfrisser * Java heeft Anon. classes -> beperkingen, verbose (interface nodig), daarom weinig gebruikt
- * Zijn natuurlijk allemaal op ISKA over closures geweest, maar toch een opfrisser * Java heeft Anon. classes -> beperkingen, verbose (interface nodig), daarom weinig gebruikt
- * Zijn natuurlijk allemaal op ISKA over closures geweest, maar toch een opfrisser * Java heeft Anon. classes -> beperkingen, verbose (interface nodig), daarom weinig gebruikt
- * Zijn natuurlijk allemaal op ISKA over closures geweest, maar toch een opfrisser * Java heeft Anon. classes -> beperkingen, verbose (interface nodig), daarom weinig gebruikt
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- * Function0 tot Function22 op deze manier beschikbaar
- Scala gaat nog verder, zelf control structures maken (by-name params)
- * First trait/class with extends, then 0 or more times with * Traits can have any member: defs, abstract defs, fields traits can extend from each other
- * Traits are used in this fashion a lot for the Scala collection libs
- * abstract override: target of super not known at design-time! * calls resolve right-to-left * selftype annotation: type of this can assume type of class where trait is mixed in!
- * abstract override: target of super not known at design-time! * calls resolve right-to-left * selftype annotation: type of this can assume type of class where trait is mixed in!
- * abstract override: target of super not known at design-time! * calls resolve right-to-left * selftype annotation: type of this can assume type of class where trait is mixed in!
- * geen new keyword nodig: case class is class + companion object met apply method! * Sealed abstract class: compiler kan checken of alle cases gedekt zijn
- * geen new keyword nodig: case class is class + companion object met apply method! * Sealed abstract class: compiler kan checken of alle cases gedekt zijn
- * geen new keyword nodig: case class is class + companion object met apply method! * Sealed abstract class: compiler kan checken of alle cases gedekt zijn
- * Twee doelen: selecteren goede case, en binden van variabelen in 1 stap * Java kent heeeel beperkte pattern matching: catch-clauses * Geen NPE: helaas heeft Scala wel null, vanwege compatibility -> tradeoff * voorbeelden van option: Map.get, List.find, parseInt, etc.
- * Twee doelen: selecteren goede case, en binden van variabelen in 1 stap * Java kent heeeel beperkte pattern matching: catch-clauses * Geen NPE: helaas heeft Scala wel null, vanwege compatibility -> tradeoff * voorbeelden van option: Map.get, List.find, parseInt, etc.
- * match is an expression too
- * Of course case objects can be used to implement enums
- * Of course case objects can be used to implement enums
- * Of course case objects can be used to implement enums
- * Of course case objects can be used to implement enums
- * Of course case objects can be used to implement enums
- Ook test frameworks
- Proberen stukje realworld code van Java->Scala als Java programmeur->Idiomatische Scala
- * TIOBE top-30: beating Groovy, Haskell
- * TIOBE top-30: beating Groovy, Haskell
- Java -> Scala voorbeeld: een Scala - methode wordt vertaald naar $minus$. Veel conventies voor compiler gegenereerde classes.