The FP ecosystem in Kotlin

Arrow is a Kotlin library that has brought support for HKTs and type classes into the language. On top of that we have ported a good chunk of the FP stack including comprehensions, lenses, recursion schemes, and a blazing fast effects system. This enables experimenting with Haskell papers that you can seamlessly run on your phone.

The other aspect of Arrow is that it’s already widespread in the industry and is being used by startups and banks. It works on top of the vanilla Kotlin toolset, so it is safe to bring into your JVM programs. Bring your favorite FP constructs onto your day-to-day job!

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1. @pacoworks
   Paco Estevez
   “Stop ****ing up our
   language”
   The FP ecosystem in Kotlin
   

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2. @pacoworks
   Arrow: arrow-kt.io
   2
   

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3. @pacoworks
   Version 0.10 - Released this month!
   2.5 years running
   3
   

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4. @pacoworks
   Stop
   4
   First interaction with Kotlin leadership
   

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5. @pacoworks
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   Meme:
   
   “I’m Spanish but I haven’t come to
   talk about FP”
   

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6. @pacoworks
   Funktionale + Kategory = Arrow
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7. @pacoworks
   Tens of known Apps, as many backends
   Talks around the world
   Multiple books
   3k Github stars
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8. @pacoworks
   Consultancies
   8
   Legitimate now
   

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9. @pacoworks
   What is in it?
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10. @pacoworks
    Boring libraries
    10
    Prelude
    Effect system
    Optics
    Metaprogramming utils soon
    

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11. @pacoworks
    Incubator libraries
    11
    Recursion Schemes
    MTL
    Free
    AQL
    Streams
    Collections
    

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12. @pacoworks
    Most important contribution?
    12
    

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13. @pacoworks
    13
    

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14. @pacoworks
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15. @pacoworks
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16. @pacoworks
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17. @pacoworks
    Arrow Docs
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20. @pacoworks
    Arrow Fx
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21. @pacoworks
    Principles
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    Based off existing research
    Uses coroutines
    Flattened IO combinators
    

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22. @pacoworks
    Primitives
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    fx for syntax
    effect to wrap
    ! to compute
    

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24. @pacoworks
    Future of Fx
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    Bifunctor IO
    Reader + Bifunctor IO
    Streams
    

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25. @pacoworks
    Arrow Core
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26. @pacoworks
    Prelude I
    26
    Anaemic stdlib
    Datatypes
    

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27. @pacoworks
    Kind
    27
    

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28. @pacoworks
    F
    28
    

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29. @pacoworks
    class ForList private constructor()
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30. @pacoworks
    class ForSequence private constructor()
    class ForOption private constructor()
    class ForTry private constructor()
    class ForId private constructor()
    class ForSet private constructor()
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31. @pacoworks
    Kind
    isomorphism
    Option
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    <---
    <---
    

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32. @pacoworks
    class Option: Kind
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33. @pacoworks
    fun Kind.fix(): Option =
    33
    

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34. @pacoworks
    Extension functions are checked at compile time
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35. @pacoworks
    fun Kind.fix(): Option =
    this as Option
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    Safe!
    Pinkie promise
    Totally ok
    
    

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36. @pacoworks
    Prelude II
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    Anaemic stdlib
    Datatypes
    Typeclasses
    

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37. @pacoworks
    fun Kind.map(
    f: (A) -> B,
    ): Kind
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38. @pacoworks
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40. @pacoworks
    Arrow Meta
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41. @pacoworks
    Tinkering…
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    Quasiquoting
    Hacking the typechecker
    Purity checker
    Coherent typeclass implementation
    

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42. @pacoworks
    …in the real world
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    Early days
    Lots of potential experiments
    Focus on industrial uses
    

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43. @pacoworks
    Growing an ecosystem
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44. @pacoworks
    Letting talent flourish
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    Optics - Simon Vergauwen
    Recursion Schemes - Aedan Smith
    Free - Pablo Guardiola
    

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45. @pacoworks
    Sister projects
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    Ank
    Helios
    Kessel
    Hoplite
    KotlinTest
    

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46. @pacoworks
    Papers in Practice
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    The Frank language: Do be do be do
    Selective Applicative Functors
    Build Systems a la Carte
    Defunctionalized Kind Projections
    

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47. @pacoworks
    Come join us!
    47
    

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48. @pacoworks
    Community ❤
    gitter.im/arrow-kt/
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    138 github contributors
    Gitter.im chat
    Kotlinlang slack #arrow
    

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49. @pacoworks
    Arrow: arrow-kt.io
    pacoworks.com
    @pacoworks
    github.com/pakoito
    Slides: tinyurl.com/ArrowAle19
    49
    Special thanks to all
    Arrow contributors &
    supporters!
    

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