Functional Programming in Groovy
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This document summarizes a presentation on functional programming in Groovy. It introduces functional programming concepts like immutable state, recursion, and first-class functions. It then demonstrates how to apply these concepts in Groovy using tools like anonymous functions, collection methods for filtering, mapping and folding, memoization, and parallelism with GPars. Finally, it suggests areas of code that are good candidates for a functional approach, such as replacing loops with collection methods and splitting operations into filter, map and fold steps.
Functional Programming in Groovy
- 1. Functional Programming 101 in Groovy Evgeny Goldin DevCon Tel-Aviv, February 14, 2013
- 2. Evgeny Goldin Java developer since 2000 FP enthusiast: Scheme, Perl, Groovy, Scala GroovyMag, Gr8Conf SCM at Trademob github.com/evgeny-goldin/ @evgeny_goldin
- 5. In this session Why FP? FP building blocks FP in Groovy FP candidates
- 6. In this session Mindset switch
- 7. Why FP?
- 9. .. or do we make it happen?
- 10. Average code is complex Side-effects go wild Logical steps are interleaved Changes are error-prone http://www.guardian.co.uk/sustainable-business/research-confirms-health-impacts-tire
- 11. Average state is fragile and shared Exposed for updates in any way Can easily mutate under your feet Changes are error-prone http://www.bbcgoodfood.com/content/knowhow/glossary/egg/
- 12. Parallelism is hard “The Multicore Revolution” Threads + shared mutable state :( Changes are error-prone http://www.russel.org.uk/Presentations/euroPython2010_theMulticoreRevolution.pdf http://jalopnik.com/5965581/this-is-how-not-to-parallel-park-on-a-hill
- 15. Modularity Break the flow into distinct steps Do one thing and do it well
- 17. Testability Ensure correctness of your steps
- 19. FP building blocks (only a subset this time)
- 20. Recursion List = head() + tail() State is hidden, built up on stack Recursion elimination https://bitbucket.org/evgenyg/devcon-2013/src/master/recursion.groovy
- 21. Immutable State Moving parts are minimized No defensive copying Caching, Parallelism
- 22. Immutable State New state = f ( old state ) Changes are isolated, constructor only g ( i + 1 ), g ( list + ‘element’ )
- 23. Immutable State Persistent data structures Updated in place Yields a new immutable state
- 25. First-class functions Anonymous functions Higher-order functions Command/Template/Visitor => “Free Willy”
- 26. No side-effects sin, cos, max, min, sum, sort Opens doors for optimizations Caching, Parallelism
- 27. Mindset switch Imperative => Functional Variables => Values Classes => Functions Explicit instructions => Declarative definitions How (Steps) => What (Result)
- 28. Mindset switch Pointers, memory allocations, GC - check State management Iterations Filtering, conversion, folding Parallelism
- 29. FP in Groovy
- 30. Gradual conversion http://www.buysgmath.com/p/200/eph-gradually-difficulty-mathematics-1/
- 31. final j = 5 @Immutable
- 32. Anonymous Functions a.k.a. Closures
- 33. Filter - findAll() Map - collect() Fold - inject() https://bitbucket.org/evgenyg/devcon-2013/src/master/functions.groovy http://www.barlifeuk.com/index.php/2012/08/enter-the-janneau-armagnac-three- musketeers-inspired-competition/
- 34. find() any() every() each() eachWithIndex() takeWhile() dropWhile()
- 35. Collection Range Map Array String ... Object.iterator()
- 36. Categories, Meta, Extensions public static <T> Collection<T> findAll(Collection<T> self, Closure filter) public static <T> List<T> collect(Collection<?> self, Closure<T> transform) public static T inject(Collection<T> self, Closure<V> closure) public static <T> T head(List<T> self) public static <T> List<T> tail(List<T> self) ... org.codehaus.groovy.runtime.DefaultGroovyMethods
- 37. Memoization a.k.a. Caching https://bitbucket.org/evgenyg/devcon-2013/src/master/memoization.groovy
- 38. Trampoline Recursion => Loop (no stack overflow) https://bitbucket.org/evgenyg/devcon-2013/src/master/trampoline.groovy
- 39. GPars! Data Parallelism https://bitbucket.org/evgenyg/devcon-2013/src/master/gpars.groovy
- 40. eachParallel() collectParallel() findAllParallel() everyParallel() foldParallel() sumParallel() gmemoize()
- 41. FP Candidates
- 42. Loops => any / every https://bitbucket.org/evgenyg/devcon-2013/src/master/loops.groovy http://en.hdyo.org/tee/questions
- 43. Split, filter, map, fold https://bitbucket.org/evgenyg/devcon-2013/src/master/map-reduce.groovy https://bitbucket.org/evgenyg/devcon-2013/src/master/check-versions.groovy http://www.cityofwaterfalls.ca/hermitage_cascade.html
- 44. Open your eyes
- 45. pinboard.in/u:evgenyg/t:fp/ Arturo Herrero - Functional Programming with Groovy Neal Ford - Functional Thinking Martin Odersky - FP Principles in Scala Erik Meijer - FP Fundamentals MIT - Structure and Interpretation of Computer Programs University of Washington - Programming Languages Stanford - Programming Paradigms