Discovering functional treasure in idiomatic Groovy

1. Discovering Functional Treasure in Idiomatic Groovy Naresha K Enteleki Solutions ! naresha.k@gmail.com @naresha_k

2. An imperative language on JVM A dynamic with Functional Flavour

3. The origin http://radio-weblogs.com/0112098/2003/08/29.html initial idea was to make a little dynamic language which compiles directly to Java classes and provides all the nice (alleged) productivity beneﬁts - James Strachan

4. Prerequisites

5. Function ! def sayHello(){! ! println 'Hello'! }! ! sayHello()!

6. Closure def wish = {! ! println "Hello"! }! ! wish() def wishFriend = {! ! println "Hello $it"! } ! ! wishFriend 'Raj' def wishFriend = { to ->! ! println "Hello $to"! }! ! wishFriend 'Raj'

7. Closure - No Arg def wish = { ->! ! println "Hello"! }! ! wish()

8. Closure - Multiple args def wishWithMessage = { to, message ->! ! println "Hello $to, $message"! }! ! wishWithMessage "Raj", "Good Evening"

9. Closures = Power functions def wishWithMessage = { to, message ->! ! println "Hello $to, $message"! }! ! wishWithMessage "Raj", "Good Evening" def <var> = <closure> Functions as Values

10. Sample Data import groovy.transform.ToString! ! @ToString(includeNames=true)! class Geek{! String name! int age! List<String> languages! } def geeks = []! geeks << new Geek(name: 'Raj', age: 24, ! ! languages: ['Java', 'Groovy'])! geeks << new Geek(name: 'Arun', age: 35, ! ! languages: ['Java', 'Scala', 'Clojure'])! geeks << new Geek(name: 'Kumar', age: 28, ! ! languages: ['Groovy', 'Scala'])!

11. Geeks who can speak Groovy def findGroovyGeeksImperative(geeks){! ! def groovyGeeks = []! ! for(geek in geeks){! ! if(geek.languages.contains('Groovy')){! ! groovyGeeks << geek! ! }! ! }! ! groovyGeeks! }

12. Geeks who can speak Groovy def findGroovyGeeksImperative(geeks){! ! def groovyGeeks = []! ! for(geek in geeks){! ! if(geek.languages.contains('Groovy')){! ! groovyGeeks << geek! ! }! ! }! ! groovyGeeks! }

13. Generalised def findGeeks(geeks, String language){! ! def knowsLang = []! ! for(geek in geeks){! ! if(geek.languages.contains(language)){! ! knowsLang << geek! ! }! ! }! ! knowsLang! }!

14. Towards Idiomatic Groovy def findGroovyGeeksFunctional(geeks){! ! geeks.findAll({it.languages.contains('Groovy')})! } def findGroovyGeeksFunctional(geeks){! ! geeks.findAll() {it.languages.contains('Groovy')}! } def findGroovyGeeksFunctional(geeks){! ! geeks.findAll {it.languages.contains('Groovy')}! }

15. Reusable def knowsGroovy = { geek -> ! ! geek.languages.contains('Groovy')! }! ! def findGeeksFunctional(geeks, criterion){! ! geeks.findAll(criterion)! }! ! println findGeeksFunctional(geeks, knowsGroovy) Higher Order Functions

16. Strategy Pattern def knowsGroovy = { geek -> ! ! geek.languages.contains('Groovy')! }! ! def knowsClojure = { geek ->! ! geek.languages.contains('Clojure')! }! ! def findGeeksFunctional(geeks, criterion){! ! geeks.findAll(criterion)! }! ! println findGeeksFunctional(geeks, knowsGroovy)! println findGeeksFunctional(geeks, knowsClojure)

17. Command Pattern def sayHello = {! ! println "Hello"! }! ! def sayHi = {! ! println "Hi"! }! ! [sayHello, sayHi].each{ command ->! ! command()! }

18. Execute Around def sayHello = {! ! println "Hello"! }! ! def sayHi = {! ! println "Hi"! }! ! [sayHello, sayHi].each{ command ->! ! println "Before Command"! ! command()! ! println "After Command"! }

19. Code Smell! def knowsGroovy = { geek -> ! ! geek.languages.contains('Groovy')! }! ! def knowsClojure = { geek ->! ! geek.languages.contains('Clojure')! }

20. After DRYing def knowsLanguage = { geek, language ->! ! geek.languages.contains(language)! }! ! def findGeeks(geeks, criterion, String language){! ! geeks.findAll {criterion(it, language)}! }! ! println findGeeks(geeks, knowsLanguage, 'Groovy')

21. A Better Approach def knowsLanguage = { geek, language ->! ! geek.languages.contains(language)! }! ! def knowsGroovy = knowsLanguage.rcurry('Groovy')! def knowsClojure = knowsLanguage.rcurry('Clojure')! ! def findGeeks(geeks, criterion){! ! geeks.findAll(criterion)! }! ! println findGeeks(geeks, knowsGroovy)! println findGeeks(geeks, knowsClojure) Curried Functions

22. Geeks • Knows Groovy • At least 25 years old

23. Composing em def atleast25YearsOld = { geek ->! ! geek.age >= 25! }! ! def findGeeks(geeks, criterion){! ! geeks.findAll(criterion)! }! ! def findGroovyGeeks = (this.&findGeeks)! ! .rcurry(knowsGroovy)! def findGeeksAtLeast25 = (this.&findGeeks)! ! .rcurry(atleast25YearsOld) def findGroovyGeeksOlderThan24 = ! ! findGeeksAtLeast25 << findGroovyGeeks! ! println findGroovyGeeksOlderThan24(geeks) Function Composition

24. Towards Immutable Data def geeks = []! geeks << new Geek(name: 'Raj', age: 24, ! ! languages: ['Java', 'Groovy'])! geeks << new Geek(name: 'Arun', age: 35, ! ! languages: ['Java', 'Scala', 'Clojure'])! geeks << new Geek(name: 'Kumar', age: 28, ! ! languages: ['Groovy', 'Scala']) geeks2 = geeks + new Geek(name: 'Mark', age: 40, ! ! languages: ['Lisp', 'Haskell']) geeksImmutable = geeks.asImmutable()

25. Towards Immutable Data … def geeksOrderedByAge = geeks.sort { it.age }! println geeksOrderedByAge! println geeks def geeksOrderedByAge = geeks.sort false, { it.age }! println geeksOrderedByAge! println geeks Pure Functions

26. Demo

27. import groovy.transform.*! ! @TailRecursive! def factorial(number, fact = 1){! ! number == 0 ? fact : factorial(number - 1, fact * number)! }! ! println factorial(2500G) Tail Call Optimization

28. Prior to Groovy 2.3 def fact! fact = { number, result ->! ! number == 0 ? result : ! ! ! fact.trampoline(number-1, result * number)! }.trampoline()

29. Slow Functions

30. import groovy.transform.*! ! @Memoized! def timeConsumingOperation(int number){! ! println "Performing computation"! ! number * number! }! ! println timeConsumingOperation(2)! println timeConsumingOperation(2) Memoization

31. Map Filter Reduce println geeks.findAll { it.languages.contains('Groovy')}! ! ! ! .collect {it.age}! ! ! ! .sum()! ! println geeks.findAll { it.languages.contains('Groovy')}! ! ! ! .collect {it.age}! ! ! ! .with{ sum()/ size()}

32. Defer

33. Defer import groovy.transform.*! ! class Website{! ! String address! ! @Lazy ! ! URL url = address.toURL()! }! ! ! def fuconf = new Website(address: 'http://functionalconf.com/')! println fuconf.dump()! ! def content = fuconf.url.text! println content.grep("n").size()! println fuconf.dump()! Lazy Evaluation

34. Recursion vs Iteration

35. Recursion vs Iteration def ages = geeks.collect { it.age }! ! def sum! sum = { head, tail ->! ! if(!tail){! ! ! head! ! }! ! else{! ! ! head + sum(tail.head(), tail.tail())! ! }! }! ! println(sum(0, ages))

36. Recursion vs Iteration println ages.inject(0) { s, item ->! ! s + item! }

37. The Ultimate Lesson https://twitter.com/mfeathers/status/29581296216

38. Functional Treasures Functions as values (First class citizens) Higher order functions Curried Functions Function Composition Pure Functions (Immutability) Tail Call Optimization Memoization Lazy Evaluation

39. Welcome to

40. References • https://github.com/naresha/functionalconf2014