Pragmatist’s Guide to Functional Geekery

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

@miciek Let’s talk functional!

@miciek

@miciek Galactic Twitter, one week.

@miciek

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

@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

@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

@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

@miciek Bringing style to

@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

@miciek Galactic Twitter, one week.

@miciek

@miciek Future<T>

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

@miciek @miciek

@miciek

@miciek Future.get is a blocking call!

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

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

@miciek

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

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

@miciek

@miciek polling every 200ms

@miciek @miciek

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

@miciek @miciek

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

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

@miciek

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

@miciek @miciek

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

@miciek @miciek

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

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

@miciek io.vavr.concurrent.Future

@miciek Pipelining potential failures

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

@miciek @miciek

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

@miciek @miciek

@miciek @miciek Future<Option<Try<List<? extends Citizen>>>> I am not happy with
the return types we use in the application!

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

@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

@miciek

@miciek How to convert Try<Integer> into RemoteFollowersData?

@miciek Pattern Matching

@miciek

@miciek @miciek

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

@miciek Clones should not count as followers!

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

@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

@miciek Pattern Matching to the rescue!

@miciek

@miciek @miciek

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

@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!

@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

@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

@miciek

@miciek or

@miciek

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

@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

@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

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

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

@miciek

@miciek Feature Switch!

@miciek @miciek

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

@miciek We used types to model our assumptions!

@miciek Standard Unit Tests

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

@miciek

@miciek @miciek

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

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

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

@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

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

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

@miciek @miciek

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

@miciek

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

@miciek Coupled concerns RemoteData RemoteData as JSON Response HTTP Server

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

@miciek Pure values, no mess!

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

@miciek Compiler will use them automatically!

@miciek

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

@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

Pragmatist’s Guide to Functional Geekery

Pragmatist’s Guide to Functional Geekery

More Decks by Michał Płachta

Other Decks in Programming

Featured

Transcript