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Functional Programming 101 in Groovy Evgeny Goldin DevCon Tel-Aviv, February 14, 2013

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Evgeny GoldinJava developer since 2000FP enthusiast: Scheme, Perl, Groovy, ScalaGroovyMag, Gr8ConfSCM at Trademobgithub.com/evgeny-goldin/@evgeny_goldin

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Are you FP-er?

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http://thecoolnessfactor.com/2013/01/winds-change/changes-ahead-exit-sign/

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In this session Why FP? FP building blocks FP in Groovy FP candidates

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In this sessionMindset switch

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Why FP?

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Because shit happens

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.. or do we make it happen?

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Average code is complex Side-effects go wild Logical steps are interleaved Changes are error-pronehttp://www.guardian.co.uk/sustainable-business/research-confirms-health-impacts-tire

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Average state is fragile and shared Exposed for updates in any wayCan easily mutate under your feet Changes are error-prone http://www.bbcgoodfood.com/content/knowhow/glossary/egg/

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Parallelism is hard “The Multicore Revolution” Threads + shared mutable state :( Changes are error-pronehttp://www.russel.org.uk/Presentations/euroPython2010_theMulticoreRevolution.pdf http://jalopnik.com/5965581/this-is-how-not-to-parallel-park-on-a-hill

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Changes are error-prone

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http://lenta.ru/sitemap.xmlhttps://bitbucket.org/evgenyg/devcon-2013/src/master/sitemap-imperative.groovyhttps://bitbucket.org/evgenyg/devcon-2013/src/master/sitemap-functional.groovy

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ModularityBreak the flow into distinct steps Do one thing and do it well

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FlexibilityShuffle your steps

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TestabilityEnsure correctness of your steps

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ParallelismScale your steps!

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FP building blocks(only a subset this time)

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Recursion List = head() + tail() State is hidden, built up on stack Recursion eliminationhttps://bitbucket.org/evgenyg/devcon-2013/src/master/recursion.groovy

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Immutable StateMoving parts are minimized No defensive copying Caching, Parallelism

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Immutable State New state = f ( old state )Changes are isolated, constructor only g ( i + 1 ), g ( list + ‘element’ )

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Immutable State Persistent data structures Updated in placeYields a new immutable state

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Githttp://git-scm.com/book/en/Git-Branching-What-a-Branch-Is

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First-class functions Anonymous functions Higher-order functionsCommand/Template/Visitor => “Free Willy”

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No side-effects sin, cos, max, min, sum, sortOpens doors for optimizations Caching, Parallelism

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Mindset switch Imperative => Functional Variables => Values Classes => FunctionsExplicit instructions => Declarative definitions How (Steps) => What (Result)

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Mindset switchPointers, memory allocations, GC - check State management Iterations Filtering, conversion, folding Parallelism

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FP in Groovy

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Gradual conversionhttp://www.buysgmath.com/p/200/eph-gradually-difficulty-mathematics-1/

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final j = 5@Immutable

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Anonymous Functions a.k.a. Closures

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Filter - findAll() Map - collect() Fold - inject() https://bitbucket.org/evgenyg/devcon-2013/src/master/functions.groovyhttp://www.barlifeuk.com/index.php/2012/08/enter-the-janneau-armagnac-three- musketeers-inspired-competition/

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find() any() every() each()eachWithIndex() takeWhile() dropWhile()

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Collection Range Map Array String ...Object.iterator()

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Categories, Meta, Extensionspublic 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

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Memoization a.k.a. Cachinghttps://bitbucket.org/evgenyg/devcon-2013/src/master/memoization.groovy

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TrampolineRecursion => Loop (no stack overflow)https://bitbucket.org/evgenyg/devcon-2013/src/master/trampoline.groovy

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GPars! Data Parallelismhttps://bitbucket.org/evgenyg/devcon-2013/src/master/gpars.groovy

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eachParallel()collectParallel()findAllParallel()everyParallel() foldParallel() sumParallel() gmemoize()

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FP Candidates

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Loops => any / everyhttps://bitbucket.org/evgenyg/devcon-2013/src/master/loops.groovy http://en.hdyo.org/tee/questions

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Split, filter, map, fold https://bitbucket.org/evgenyg/devcon-2013/src/master/map-reduce.groovyhttps://bitbucket.org/evgenyg/devcon-2013/src/master/check-versions.groovy http://www.cityofwaterfalls.ca/hermitage_cascade.html

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Open your eyes

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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 FundamentalsMIT - Structure and Interpretation of Computer Programs University of Washington - Programming Languages Stanford - Programming Paradigms

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Thank you! @evgeny_goldinevgenyg@gmail.com