Freestyle, Free & Tagless: Separation of Concerns on Steroids

You will learn how to cut your applications into isolated, independent pieces using Freestyle library with free monads or tagless final style. The session is based on a multiplayer, purely functional version of Prisoner’s Dillema.

Our applications frequently consist of business logic, communication, persistence, caches & logging. We always want to keep them apart and reason about each of them individually. However, this is very difficult to achieve in practice.

Enter free monad. It lets us decouple those concerns by dividing our program into algebras and interpreters. I will show you an application built on top of free monad in Scala & Cats. You will learn how to create pure & declarative DSLs, side-effecting interpreters and how to use them together. Then I will introduce Freestyle library and show how it makes the code more concise. At the end I will compare the free monad approach to another technique used to decouple concerns: final tagless.

Transcript

1. @miciek Michał Płachta Freestyle Free & Tagless www.michalplachta.com www.michalplachta.com Separation of Concerns on Steroids @miciek
2. @miciek Separation of Concerns… not
3. @miciek Intelligent Thinking It is, that one is willing to study in depth an aspect of one's subject matter in isolation for the sake of its own consistency, all the time knowing that one is occupying oneself only with one of the aspects. Portrait by Hamilton Richards - manuscripts of Edsger W. Dijkstra, University Texas at Austin, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4204157 “
4. @miciek Separate All the Things! High Level Logic Business #1 Business #2 Logging Metrics DB Access Low Level Logic High Level Logic Low Level Logic business concern technical concern
5. @miciek Separate All the Things! High Level Logic Business #1 Business #2 Logging Metrics DB Access Low Level Logic High Level Logic Low Level Logic business concern technical concern knows about
6. @miciek No outgoing arrows = separated High Level Logic Business #1 Business #2 Logging Metrics DB Access Low Level Logic High Level Logic Low Level Logic
7. @miciek Developer Experience Intended Design Real Life Usage https://i.imgur.com/JIXACph.jpg Developer Experience
8. @miciek Developer Experience Database https://i.imgur.com/JIXACph.jpg Business #1 High Level Logic Low Level Logic DB Access
9. @miciek Developer Experience https://cdn-images-1.medium.com/max/1920/1*WeZlYd1Exr2JVup0MeSwaw.jpeg
10. @miciek We’ll use Free Free[F, A] A program that uses language F to produce A
11. @miciek Journey Prisoner’s Dilemma 3 apps 15 overlapping concerns using Cats & Freestyle more Freestyle Tagless Final hardcore concern separation
12. @miciek Prisoner’s Dilemma Simple example with non-trivial mechanics...
13. @miciek Prisoner’s Dilemma
14. @miciek Prisoner’s Dilemma
15. @miciek Prisoner’s Dilemma The other prisoner is GUILTY! I prefer to remain SILENT or
16. @miciek Prisoner’s Dilemma GUILTY! GUILTY! 3 years 3 years
17. @miciek Prisoner’s Dilemma GUILTY! GUILTY! 3 years 3 years ... ... 1 year 1 year
18. @miciek Prisoner’s Dilemma GUILTY! GUILTY! 3 years 3 years ... ... 1 year 1 year GUILTY! ... FREE 3 years
19. @miciek Prisoner’s Dilemma GUILTY! GUILTY! 3 years 3 years ... ... 1 year 1 year GUILTY! ... FREE 3 years ... GUILTY! 3 years FREE
20. @miciek Repeated Prisoner’s Dilemma http://ncase.me/trust/
21. @miciek Journey Prisoner’s Dilemma 3 apps 15 overlapping concerns using Cats & Freestyle more Freestyle Tagless Final
22. @miciek Hot Seat Game Welcome to Hot Seat Game, Prisoner A! What's your name? > Adam Hello, Adam! Welcome to Hot Seat Game, Prisoner B! What's your name? > Jane Hello, Jane!
23. @miciek Hot Seat Game Welcome to Hot Seat Game, Prisoner A! What's your name? > Adam Hello, Adam! Welcome to Hot Seat Game, Prisoner B! What's your name? > Jane Hello, Jane! Adam, is Jane guilty? > n Your decision: Silence Jane, is Adam guilty? > n Your decision: Silence Verdict for Adam is 1 year Verdict for Jane is 1 year
24. @miciek Hot Seat Game
25. @miciek Hot Seat Game
26. @miciek Hot Seat Game
27. @miciek Hot Seat Game Concerns Hot Seat Logic business concern technical concern knows about
28. @miciek Hot Seat Game Concerns Hot Seat Logic Computing Verdict Player Interaction Player Communication using Console business concern technical concern knows about
29. @miciek Hot Seat Game Concerns Hot Seat Logic Computing Verdict Player Interaction Player Communication using Console
30. @miciek Hot Seat Game Concerns Hot Seat Logic Computing Verdict Player Interaction Player Communication using Console Free[F, A]
31. @miciek Computing Verdict Concern #1
32. @miciek Player Interaction Concern #2 Operation name Return value
33. @miciek Player Interaction Concern #2
34. @miciek Hot Seat Logic Concern #3
35. @miciek Hot Seat Logic Concern #3
36. @miciek Player Interaction using Console Concern #4 How to transform Player[A] into IO[A]?
37. @miciek Player Interaction using Console Concern #4 How to transform Player[A] into IO[A]?
38. @miciek Player Interaction using Console Concern #4 How to transform Player[A] into IO[A]?
39. @miciek Player Interaction using Console Concern #4
40. @miciek Connecting the Dots Hot Seat Logic Computing Verdict Player Interaction Player Communication using Console pure function Free[Player, A] Player[A] ~> IO[A] Free[S, Unit]
41. @miciek End of the World
42. @miciek End of the World
43. @miciek End of the World
44. @miciek Practical Problems with Free #1 Boilerplate
45. @miciek Freestyle which is built on top of Cats
46. @miciek After Freestyle No Boilerplate Algebra
47. @miciek After Freestyle No Boilerplate Interpreter
48. @miciek After Freestyle No Boilerplate Interpreter
49. @miciek Playing with a Bot Adding new features is adding more concerns!
50. @miciek Playing with a Bot Welcome to Single Player Game! What's your name? > Michal Hello, Michal! Michal, is WALL-E guilty? > n Your decision: Silence Verdict for Michal is 1 year Adding new features is adding more concerns!
51. @miciek Reusing Values Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction #1 #2 #3 Bot Opponent
52. @miciek Opponent Interaction Freestyle generates all the case classes and other helpers!
53. @miciek Unknown Opponent Logic
54. @miciek Unknown Opponent Logic
55. @miciek Friend’s Reaction
56. @miciek End of the World
57. @miciek End of the World
58. @miciek End of the World ???
59. @miciek Bot Opponent
60. @miciek End of the World
61. @miciek Workflow 1. Define operations 2. Create programs 3. Try to run them 4. Fix errors by implementing interpreters Player Interaction Unknown Opponent Unknown Opponent
62. @miciek Different Interpreter for Opponent? Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction ? Bot Opponent
63. @miciek Remote Opponent Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction Remote Opponent Bot Opponent
64. @miciek Meeting Remote Opponent Player A Player B RegisterAsWaiting GetWaitingPlayers JoinWaitingPlayer CheckIfOpponentJoined UnregisterWaiting found Player A found Player B
65. @miciek Matchmaking
66. @miciek Matchmaking Programs Player A Player B waitForOpponent findOpponent RegisterAsWaiting GetWaitingPlayers JoinWaitingPlayer CheckIfOpponentJoined UnregisterWaiting
67. @miciek Find Opponent
68. @miciek Find Opponent
69. @miciek Remote Opponent Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction Remote Opponent Bot Opponent
70. @miciek Bot Opponent Recap:
71. @miciek Remote Opponent What should we interpret Opponent into? ???
72. @miciek Remote Opponent We should interpret Opponent into Free
73. @miciek Workflow 1. Define operations 2. Create programs 3. Try to run them 4. Fix errors by implementing interpreters Player Interaction Unknown Opponent Unknown Opponent
74. @miciek Recap: Game with a Bot Unknown Opponent Logic Opponent Interaction Bot Opponent var state: Map ...
75. @miciek Interpreting into Free Unknown Opponent Logic Opponent Interaction Bot Opponent var state: Map ... Remote Opponent is interpreting into another Free program! Remote Opponent
76. @miciek Multiplayer Game Mode Opponent Interaction Remote Opponent Matchmaking ? Let’s zoom in!
77. @miciek Multiplayer Game Mode Opponent Interaction Remote Opponent Matchmaking Remote Actor Matchmaker
78. @miciek Matchmaking Recap:
79. @miciek Matchmaking Server Handler
80. @miciek End of the World
81. @miciek End of the World
82. @miciek End of the World
83. @miciek 3 Game Modes = 15 Concerns + 31 Tests Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction Remote Opponent Bot Opponent Decision Registry Matchmaking Matchmaking Server Decision Server Timing Hot Seat Logic EoW Thread Timing x3 Player Local Interaction
84. @miciek 3 Game Modes = 15 Concerns + 31 Tests Computing Verdict Player Interaction Player Communication using Console Unknown Opponent Logic Opponent Interaction Remote Opponent Bot Opponent Decision Registry Matchmaking Matchmaking Server Decision Server Timing Hot Seat Logic EoW Thread Timing x3 Player Local Interaction Thread.sleep println var
85. @miciek Journey Prisoner’s Dilemma 3 apps 15 overlapping concerns using Cats & Freestyle more Freestyle Tagless Final
86. @miciek Freestyle Composing Algebras using Modules
87. @miciek Pure Cats Composing Algebras using Coproducts
88. @miciek Pure Cats Free Creating Lots of Objects
89. @miciek Journey Prisoner’s Dilemma 3 apps 15 overlapping concerns using Cats & Freestyle more Freestyle Tagless Final
90. @miciek Final Tagless Instead of wrapping everything in Free
91. @miciek Final Tagless Let’s execute instructions directly! F can be anything!
92. @miciek Final Tagless using Freestyle
93. @miciek Course of Action ▪ Use Free directly using cats or scalaz ▪ Use Final Tagless directly ▪ When comfortable, start using freestyle ▪ Decide @tagless or @free per use case
94. @miciek @free or @tagless? @free @tagless program is data program is an expression plain values expressions parametrized by F[_] stack-safe stack-safe iff F[_] is stack-safe Remember: Mix and match your algebras using Freestyle! More here: https://softwaremill.com/free-tagless-compared-how-not-to-commit-to-monad-too-early/ Note that Freestyle gets rid of some problems mentioned there!
95. @miciek Learn More https://github.com/miciek/free-prisoners 6 apps / 3 in Free / 3 in Freestyle / 2 Akka actors / 31 tests
96. @miciek Michał Płachta www.michalplachta.com THANKS! Freestyle Free & Tagless https://github.com/miciek/free-prisoners 6 pure apps / 15 concerns / 2 Akka actors / 31 tests @miciek