A Programmer’s Red Pill: Pure, Functional, and Typed

An introduction to 3 red pills that will make you not look at your programming language the same way again

Transcript

1. A Programmer’s Red Pill Pure, Functional, and Typed @choonkeat Feb 2021
2. Warning “Actually, I hate you with all my soul because after going the route of pure functional language with union types.. there is no way back” “my whole life is a lie”
3. About • C, Perl, Java • Javascript & Ruby on Rails for 10 years • Go and Elm in the past few years • @choonkeat
4. Dynamically Typed
5. Hidden Static Typed function body code de fi nes the type in a long-winded way
6. Hidden Static Typed user of your code sees nothing
7. 🤔 can you spot the problem? Hidden Static Typed
8. Hidden Static Typed 🤔 can you spot the problem? Nit 😝
9. Hidden Static Typed 🤔 can you spot the problem? Nit 😝 Nit 😝
10. LGTM 👍 🚢 Hidden Static Typed
11. Hidden Static Typed
12. Duck Type uck!
13. “Software engineering is what happens to programming when you add time and other programmers.” — Russ Cox https://research.swtch.com/vgo-eng
14. Stack trace we can be pretty good detectives
15. But wouldn’t it be better…
16. Tell me earlier Booting Compiling Run locally PR Review CI Running Twitter
17. Tell me where
18. Oh… must write Types now? 🙄
19. Hindley–Milner Type Inference Est. Since 1982
20. Hindley–Milner Type Inference Est. Since 1982 COVID-19 2000 1960 Java Ruby Javascript C Go 1980 Haskell Elm Python Standard ML
21. Look Ma, No Types!
22. Tell me where (Recap)
23. Duck Type uck!
24. What’s the hidden type of `user`
25. What’s the hidden type of `user`
26. 0m0.076s *compiler speed and friendliness of error message may defer between languages
27. Where error happened Where mistake was made Runtime errors Error when I save my fi le
28. Where error happened Where mistake was made Runtime errors Error when I save my fi le
29. Where error happened Where mistake was made Runtime errors Error when I save my fi le https://elm-lang.org/news/compilers-as-assistants
30. Compiler Driven Development “ Change parts of the code and then let the compiler errors guide you in the rest of the task. Then rinse and repeat.
 ” https://dev.to/lucamug/elm-6m8
31. https://ellie-app.com/chWMjHk6fbMa1 Hands on
32. Compiler Driven Development “ Change parts of the code and then let the compiler errors guide you in the rest of the task. Then rinse and repeat.
 ” https://dev.to/lucamug/elm-6m8
33. TDD https://youtu.be/a6oP24CSdUg
34. TDD https://youtu.be/a6oP24CSdUg
35. TDD https://youtu.be/a6oP24CSdUg
36. GTD “I really like this approach of testing, it just walks you through: what’s the next step I have to do to get this working. ” http://railscasts.com/episodes/275-how-i-test
37. TDD • This is what I have • This is what I need • Make it work
38. TDD • This is what I have • This is what I need • Make it work
39. TDD • This is what I have • This is what I need • Make it work Given Expect
40. Given Expect TDD • This is what I have • This is what I need • Make it work Code
41. Given Expect TDD • This is what I have • This is what I need • Make it work Code Write test harness
42. • This is what I have • This is what I need • Make it work Code But wouldn’t it be better…
43. TDD • This is what I have • This is what I need • Make it work Code Function Signature
44. 🌈 Function Signature? 🌈 O Rly?
45. 🌈 Function Signature? 🌈 O Rly?
46. 🌈 Function Signature? 🌈 • Is the given URL fetched and JSON data parsed as User? • Are we connecting to some DB to get User? • What if `User` and `error` are both nil? Are both NOT nil?
47. 🌈 Function Signature? 🌈
48. 🌈 Function Signature? 🌈
49. Function Signature Function Signature in Pure Type FP
50. Pure Function • Its return value is the same for the same arguments • No side e ff ects; doesn’t change anything else anywhere
51. GTD: Solve Smaller Problems • Custom Types to narrow problem surface • Solve small parts of bigger problems — regardless of whether your codebase is 50 or 500,000 LOC, focus only in the current function body • Easily assemble without baggage because functions are pure • Refactoring: establish new ideals then solve errors
52. Example Problem: Routing
53. Software Engineering
54. Software Engineering
55. Constant Vigilance Functional architecture - The pits of success - Mark Seemann https://youtu.be/US8QG9I1XW0
56. Adapters Ports Design Pattern + Best Practices Core
57. “I’m more interested in functional techniques than functional languages
 Adapters Ports Design Pattern + Best Practices Core • avoid shadowing variables • avoid cyclic dependency • avoid inheritance • avoid mutation • prefer explicit dependency • prefer stateless functions • pure functions are testable • …
58. “I’m more interested in functional techniques than functional languages
 Adapters Ports Design Pattern + Best Practices Core • avoid shadowing variables • avoid cyclic dependency • avoid inheritance • avoid mutation • prefer explicit dependency • prefer stateless functions • pure functions are testable • …
59. “Software engineering is what happens to programming when you add time and other programmers.” — Russ Cox https://research.swtch.com/vgo-eng
60. “I’m more interested in functional techniques than functional languages
 Adapters Ports Soft Social Contract Core • avoid shadowing variables • avoid cyclic dependency • avoid inheritance • avoid mutation • prefer explicit dependency • prefer stateless functions • pure functions are testable • …
61. Adapters Ports Soft Social Contract Core other people’s code urgent fi x • avoid shadowing variables • avoid cyclic dependency • avoid inheritance • avoid mutation • prefer explicit dependency • prefer stateless functions • pure functions are testable • … “I’m more interested in functional techniques than functional languages

62. Adapters Ports Soft Social Contract Core Compiler: LGTM 🚢 other people’s code urgent fi x
63. Life with Footguns optional static typing multi-paradigm programming language functional libraries immutable.js
64. Life without Footguns Functional architecture - The pits of success - Mark Seemann https://youtu.be/US8QG9I1XW0
65. Life without Footguns Functional architecture - The pits of success - Mark Seemann https://youtu.be/US8QG9I1XW0 How?
66. Warning: No “Freedom” Runtime Your Code
67. Runtime Warning: No “Freedom”
68. Runtime Warning: No “Freedom” Spend your energy elsewhere
 e.g. gofmt elm-format
69. You Cannot Any How
70. You Cannot Any How
71. Pure Functional Program Runtime Your Program
72. Pure Functional Program Runtime Your Program Arguments in Return values
73. Pure Functional Program Runtime Your Program Http request Render DOM Call Javascript Http response Input change Mouse move
74. I Know This! 🦖🏞
75. Pure Functional Program Runtime SAME callback function hooked up to ALL events Events in Return values Http request Render DOM Call Javascript Http response Input change Mouse move
76. But Does It Scale? onClick = helloworld onSubmit = helloworld onLoad = helloworld
77. But Does It Scale?
78. But Does It Scale? Routes Http Request Handlers Callbacks
79. But Does It Scale? 
 Single entry point 

80. Pure Functional Program Runtime Events in Return values Http request Render DOM Call Javascript Http response Input change Mouse move Pure Function Pure Function Pure Function Pure Function Pure Function Pure Function Pure Function Pure Function Pure Function
81. “1 big callback” ok…
82. But Pure Functions Only? String.toUpper List.reverse Array.map
83. Stateless Http Handler
84. Stateless Function instead of doing it…
85. Pure Function
86. Pure Http Handler
87. Pure Functional Program Runtime Your Callback Function Events in Return values Http request Render DOM Call Javascript Http response Input change Mouse move
88. Runtime artist impression (not real)
89. Runtime
90. Runtime
91. Life without Footguns Functional architecture - The pits of success - Mark Seemann https://youtu.be/US8QG9I1XW0
92. Pure Functional Program Runtime Your Code Msg, Model Model, Cmd Http request Render DOM Call Javascript store `Model` value Http response Input change Mouse move
93. Elm Projects elm-visualization elm-physics Elmboy - A Nintendo™ Game Boy™ Emulator written in Elm
94. Hands on https://ellie-app.com/chXtQPdLprva1
95. Elm Projects https://youtu.be/sKxEwjKQ5zg
96. Links • Elm at Rakuten https://dev.to/lucamug/elm-6m8 • How Elm Slays a UI Antipattern http://blog.jenkster.com/2016/06/how- elm-slays-a-ui-antipattern.html • Making Impossible States Impossible https://youtu.be/IcgmSRJHu_8 • Business logic in Elm that runs anywhere https://morphir. fi nos.org/ why_functional_programming • Exploring “Pure Core Imperative Shell” in Ruby https:// www.destroyallsoftware.com/talks/boundaries
97. Summary • Custom Types — describing domain models really well, unambiguously 
 see https://youtu.be/Up7LcbGZFuo • Pure and Functional — can actually be done in any language, but you get to keep your footguns. I prefer no footguns.
 see https://youtu.be/US8QG9I1XW0
98. Questions?