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@miciek Michał Płachta Pragmatist`s Guide to www.michalplachta.com Functional Geekery

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@miciek Let’s talk functional!

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@miciek

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@miciek Galactic Twitter, one week.

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@miciek

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@miciek Being functional... higher order functions immutable collections no reassignments functions immutable types

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@miciek Being functional... higher order functions -style immutable collections Guava Immutable Collections Java 8 Streams no reassignments Java final keyword functions Java 8 lambdas immutable types Lombok @Value

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@miciek Being functional... higher order functions -style built-in and more! immutable collections built-in no reassignments val keyword functions first class citizens immutable types built-in

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@miciek Being functional... higher order functions -style built-in immutable collections built-in no reassignments val keyword functions first class citizens immutable types built-in

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@miciek Bringing style to

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@miciek Being functional... higher order functions -style built-in and more! immutable collections built-in no reassignments Java final keyword functions built-in immutable types Lombok @Value

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@miciek Galactic Twitter, one week.

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@miciek

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@miciek

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@miciek

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@miciek

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@miciek Future

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@miciek Future finishes successfully with a result of type T fails with an exception

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@miciek @miciek

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@miciek

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@miciek Future.get is a blocking call!

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@miciek Citizen Future Future List Future map ??? DBClient::getFollowers

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@miciek Citizen Future Future List Future List Future map flatMap Citizen Future map Integer Future ???

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@miciek

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@miciek Future.forEach doesn’t block! :)

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@miciek io.vavr.collection.HashMap Option can be Some when value is present can be None when value is not present

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@miciek

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@miciek polling every 200ms

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@miciek @miciek

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@miciek @miciek I have 0 followers. It’s not possible.

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@miciek @miciek

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@miciek Problem: treating 0 as “no value yet”

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@miciek Problem: treating 0 as “no value yet” Solution: explicit return type Option can be Some when value is present can be None when value is not present We should use types to model our assumptions!

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@miciek

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@miciek polling every 200ms when None is returned when Some(102) is returned

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@miciek @miciek

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@miciek @miciek I can’t check how many followers does Obi-wan Kenobi have!

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@miciek @miciek

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@miciek Problem: not handling Future failures java.lang.Exception: Bad Request: citizen with name Obi-wan Kenobi couldn't be found

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@miciek Problem: not handling Future failures Solution: explicit return type (again!) Try can be Success when computation succeeded can be Failure when computation failed We should use types to model our assumptions!

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@miciek io.vavr.concurrent.Future

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@miciek Pipelining potential failures

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@miciek polling every 200ms when None is returned when Some(Success(102)) is returned when Some(Failure) is returned

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@miciek @miciek

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@miciek @miciek I am not happy with the return types you use in the application!

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@miciek @miciek

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@miciek @miciek Future>>> I am not happy with the return types we use in the application!

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@miciek Problem: cryptic, complicated types Solution: Algebraic Data Types Sum can be Something or can be SomethingDifferent We should use types to model our assumptions! can be SomethingElse or Product consists of Something and SomethingElse

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@miciek Citizen can be Civilian or can be Stormtropper can be Rebel or Stormtrooper consists of String name and boolean isCloned can be Jedi or can be Sith or ADTs

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@miciek

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@miciek

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@miciek How to convert Try into RemoteFollowersData?

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@miciek Pattern Matching

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@miciek

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@miciek

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@miciek @miciek

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@miciek @miciek Darth Vader has way too many followers! They are all clones!

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@miciek Clones should not count as followers!

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@miciek Let’s count followers! io.vavr.collections.Traversable

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@miciek Citizen any Civilian or any Stormtropper that is not cloned any Rebel or any Jedi or any Sith or Counting followers returns true if

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@miciek Pattern Matching to the rescue!

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@miciek

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@miciek @miciek

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@miciek @miciek I am not happy! Galactic Twitter is used for political purposes!

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@miciek Fear is the path to the Dark Side. Yoda Help me Obi-Wan Kenobi, you're my only hope! Princess Leia Use the Force, Luke. Obi-Wan Kenobi Very political! Not cool!

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@miciek Don’t delete, manipulate! Censorship module ● Condition: If the tweet is pro Dark Side ○ Manipulation: Add more Dark Side ● If the tweet is pro Light Side ○ Replace Force with Dark Side ● If the tweet is a general wisdom ○ Replace Force with Dark Side ○ Add more Dark Side ● If the tweet is pro Rebellion and is not a joke ○ Hail the Empire ● If the tweet is pro Empire and is a joke ○ Trash the Rebellion ● If the tweet is not pro Empire nor Rebellion ○ Add Force and even more Force ○ Make joke about it ● If the tweet is pro empire ○ Add more Dark Side ● Always ○ Sacrifice for the Empire

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@miciek No more than 2 manipulations! Censorship module initial filters ● If the tweet is pro Dark Side ○ Add more Dark Side ● If the tweet is pro Light Side ○ Replace Force with Dark Side ● If the tweet is a general wisdom ○ Replace Force with Dark Side ○ Add more Dark Side ● If the tweet is pro Rebellion and is not a joke ○ Hail the Empire ● If the tweet is pro Empire and is a joke ○ Trash the Rebellion ● If the tweet is not pro Empire nor Rebellion ○ Add Force and even more Force ○ Make joke about it ● If the tweet is pro empire ○ Add more Dark Side ● Always ○ Sacrifice for the Empire

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@miciek

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@miciek

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@miciek or

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@miciek

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@miciek Executing a List? CensorFilter Original Tweet Censored Tweet (tweet,filter) -> newTweet CensorFilter CensorFilter (tweet,filter) -> newTweet (tweet,filter) -> newTweet (tweet, filter) -> newTweet

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@miciek Executing a List of ints? 4 (0, 4) -> 0 + 4 6 3 (4, 6) -> 4 + 6 (10, 3) -> 10 + 3 Initial = 0 Output = 13 (result, x) -> result + x

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@miciek Executing a List of ints? 4 (result, x) -> result + x 6 3 (result, x) -> result + x (result, x) -> result + x Initial = 0 io.vavr.collections.List Output = 13

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@miciek CensorFilter Original Tweet Censored Tweet applyFilter CensorFilter CensorFilter applyFilter applyFilter

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@miciek CensorFilter CensorStatus (Tweet, manipulations) CensorStatus (censored Tweet, manipulations) applyFilter CensorFilter CensorFilter applyFilter applyFilter

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@miciek

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@miciek Feature Switch!

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@miciek @miciek

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@miciek @miciek You don’t have any tests!

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@miciek We used types to model our assumptions!

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@miciek Standard Unit Tests

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@miciek Problem: writing tests by examples Solution: property-based tests We should test the properties!

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@miciek

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@miciek

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@miciek @miciek

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@miciek @miciek Starring Coffeehouse Programmer Darth Vader Luke Skywalker Uncle Bob

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@miciek @miciek Directed by Future type Option type Try type “monads”

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@miciek @miciek Special Effects Algebraic Data Types Pattern Matching Property-based tests

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@miciek @miciek github.com/miciek/galactic-twitter Screenplay Java vs Scala Web server in Akka HTTP Pattern Matching implementation RemoteData as a Functor Type class pattern “Pimp my type” pattern

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@miciek @miciek (Your) Next Episode Everything as Data

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@miciek Pragmatist`s Guide to Functional Geekery github.com/miciek/galactic-twitter ANY QUESTIONS? Michał Płachta www.michalplachta.com

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@miciek @miciek

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@miciek @miciek You don’t have clean code!

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@miciek

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@miciek Concern #1: represent state of db cache Concern #2: represent RemoteData as JSON

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@miciek Coupled concerns RemoteData RemoteData as JSON Response HTTP Server

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@miciek Type class pattern RemoteData RemoteData as JSON Response RemoteData JSON Response HTTP Server HTTP Server RemoteData Tweet type class type class members

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@miciek Pure values, no mess!

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@miciek But the server needs an instance of type class!

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@miciek Compiler will use them automatically!

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@miciek

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@miciek Decoupled concerns RemoteData RemoteData as JSON Response RemoteData JSON Response HTTP Server HTTP Server RemoteData Tweet type class type class members

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@miciek Future type lib lib* built-in Option type lib lib* built-in Try type lib lib* built-in ADTs lib built-in built-in Pattern Matching lib kind of* built-in Property tests lib lib lib * more: https://github.com/MarioAriasC/funKTionale https://kotlin.link/articles/Kotlin-for-Scala-Developers.html https://programmingideaswithjake.wordpress.com/2016/08/27/improved-pattern-matching-in-kotlin/ Everything as Data