Pragmatist’s Guide to Functional Geekery

Basic functional concepts like immutable data, second-order functions, lambdas and function composition can already be found in the modern programmer’s toolkit.

During this talk you will learn about more advanced functional concepts and how they can solve real problems. I will talk about pattern matching, algebraic data types, functional abstractions, folding and property-based tests.

I will show you a practical example written using today’s Java functional constructs and build up from there. I will use only Java & Vavr, which can improve the code, make it more maintainable and testable.

Transcript

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

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2. @miciek
   Let’s talk functional!
   

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3. @miciek
   

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4. @miciek
   Galactic Twitter,
   one week.
   

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5. @miciek
   

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

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7. @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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8. @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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9. @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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10. @miciek
    Bringing style to
    

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11. @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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12. @miciek
    Galactic Twitter,
    one week.
    

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13. @miciek
    

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14. @miciek
    

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15. @miciek
    

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16. @miciek
    

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17. @miciek
    Future
    

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

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19. @miciek
    @miciek
    

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20. @miciek
    

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21. @miciek
    Future.get
    is a blocking call!
    

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

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

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24. @miciek
    

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

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26. @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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27. @miciek
    

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28. @miciek
    polling every 200ms
    

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29. @miciek
    @miciek
    

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

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31. @miciek
    @miciek
    

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

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33. @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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34. @miciek
    

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

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36. @miciek
    @miciek
    

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

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38. @miciek
    @miciek
    

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39. @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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40. @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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41. @miciek
    io.vavr.concurrent.Future
    

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42. @miciek
    Pipelining potential failures
    

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

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44. @miciek
    @miciek
    

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

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46. @miciek
    @miciek
    

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

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48. @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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49. @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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50. @miciek
    

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51. @miciek
    

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52. @miciek
    How to convert Try into
    RemoteFollowersData?
    

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53. @miciek
    Pattern Matching
    

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54. @miciek
    

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55. @miciek
    

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56. @miciek
    @miciek
    

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

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58. @miciek
    Clones should not count
    as followers!
    

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

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60. @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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61. @miciek
    Pattern Matching to the rescue!
    

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62. @miciek
    

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63. @miciek
    @miciek
    

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

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65. @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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66. @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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67. @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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68. @miciek
    

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69. @miciek
    

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70. @miciek
    or
    

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71. @miciek
    

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72. @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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73. @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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74. @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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75. @miciek
    CensorFilter
    Original
    Tweet
    Censored
    Tweet
    applyFilter
    CensorFilter CensorFilter
    applyFilter applyFilter
    

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

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77. @miciek
    

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78. @miciek
    Feature Switch!
    

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79. @miciek
    @miciek
    

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

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81. @miciek
    We used types to model
    our assumptions!
    

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82. @miciek
    Standard Unit Tests
    

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

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84. @miciek
    

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85. @miciek
    

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86. @miciek
    @miciek
    

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

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

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

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90. @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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91. @miciek
    @miciek
    (Your) Next Episode
    Everything
    as
    Data
    

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

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93. @miciek
    @miciek
    

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

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95. @miciek
    

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

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97. @miciek
    Coupled concerns
    RemoteData
    RemoteData as
    JSON Response
    HTTP Server
    

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98. @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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99. @miciek
    Pure values, no mess!
    

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

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101. @miciek
     Compiler will use them
     automatically!
     

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102. @miciek
     

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103. @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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104. @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
     

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