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Practical functional programming in JavaScript for the non-mathematician
The document discusses concepts in category theory and functional programming, emphasizing the importance of pure functions, immutability, and higher-order functions. It introduces the Kleisli category and discusses monads, currying, and the composition of functions. Examples of practical applications in JavaScript demonstrate how to implement these concepts to improve software structure and maintainability.
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Practical functional programming in JavaScript for the non-mathematician
- 1. – https://en.wikipedia.org/wiki/Kleisli_category “In category theory,a Kleisli category is a category naturally associated to any monad T. It is equivalent to the category of free T-algebras. The Kleisli category is one of two extremal solutions to the question ‘Does every monad arise from an adjunction?’”
- 2. – https://en.wikipedia.org/wiki/Kleisli_category “In category theory,a Kleisli category is a category naturally associated to any monad T. It is equivalent to the category of free T-algebras. The Kleisli category is one of two extremal solutions to the question ‘Does every monad arise from an adjunction?’”
- 3. Practical Functional Programming InJavaScript Ian Thomas (@anatomic) | December 2017
- 4. –Paul Graham “Object-oriented programmingoffers a sustainable way to write spaghetti code. It lets you accrete programs as a series of patches.”
- 6.
- 9. -Crockford’s Law (akaThe Monadic Curse) “The Monadic Curse is that once someone learns what Monads are and how to use them, they lose the ability to explain them to other people”
- 11.
- 12. –Edsger Dijkstra “Program testingcan be a very effective way to show the presence of bugs, but is hopelessly inadequate for showing their absence.”
- 13. –Simon Peyton Jones “Themost depressing thing about life as a programmer, I think, is if you’re faced with a chunk of code that either someone else wrote or, worse still, you wrote yourself but no longer dare to modify. That’s depressing.”
- 15. What is afunction?
- 16. A function relates eachelement of a set with exactly one element of another set (possibly the same set).
- 17. What is ahigher-order function?
- 18. A higher-order functionis a function which operates on another functions, either by taking them as arguments or returning them
- 19. Some principals of functionalprogramming
- 20.
- 21. Purity or, perhaps, whyshould we avoid impurity?
- 22. A pure functionis a function that, given the same input, will always return the same output and does not have any observable side effect.
- 26. How many testswould you require to adequately check this function?
- 27. Would it bemore than 6?
- 28.
- 29. Immutability goes handin hand with purity. Returning copies of data and not manipulating global state means you can guarantee certain properties and rules will always hold in your programs.
- 30.
- 31. –Ellen Ullman “We buildour computer (systems) the way we build our cities: over time, without a plan, on top of ruins.”
- 32. Imagine if youcould just build your application by putting together well tested, easily understood pieces of code in a declarative manner. Just like building with lego blocks, composition of pure functions unlocks this ability.
- 33.
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- 37. Currying is theprocess of converting a function that takes multiple arguments into a function that can take them one at a time
- 38.
- 40. “Pointfree is agood litmus test for functional code as it lets us know we've got small functions that take input to output. One can't compose a while loop, for instance. Be warned, however, pointfree is a double-edged sword and can sometimes obfuscate intention. Not all functional code is pointfree and that is O.K. We'll shoot for it where we can and stick with normal functions otherwise.” –Professor Frisby’s Mostly Adequate Guide To Functional Programming
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- 43. –Greg Nelson “To keeplarge programs well structured, you either need superhuman will power, or proper language support for interfaces.”
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- 48. Better known as…. Array(Functor) Maybe (Monad) Either (Monad) Task/Future (Monad) Reader (Monad) State (Monad) Product (Monoid) Sum (Monoid) First (Monoid) Any (Monoid) All (Monoid) Max (Monoid) Min (Monoid) Etc.
- 49. While the mathematicaldescriptions and terminology will ultimately prove useful, in many cases knowing some basic laws is enough.
- 50.
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- 52. Composition u.map(x => f(g(x)))=== u.map(g).map(f)
- 53.
- 54. Stuff I haven’t covered… Transducers Observables Lenses Foldable ReferentialTransparency Applicative Traversable Isomorphism Property based testing
- 55. Practical Example 1 Creatinga pure http client
- 56. Wrap a promisebased API using a Future
- 57. Use Reader tocreate an API which can ask for config
- 58. Use Reader patternto create an API which can ask for config
- 59. Compose our applicationrun with config
- 60. Practical Example 2 GeneratingRequestABet™ Recommendations
- 61. Customer selects bets Requestis sent to traders Nearest matches are calculated Top 4 recommendations shown
- 62. Given this asan API Response
- 63. Encapsulate business logicin pure functions
- 64. Separate out statebased operations
- 65. Compose functionality toproduce pipelines of execution
- 66.
- 67. Add some monadsto handle IO and control flow
- 68.
- 69. –Tom Cargill “The first90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time.”
- 70. Ian Thomas (@anatomic)| December 2017 Practical Functional Programming In JavaScript https://drboolean.gitbooks.io/mostly-adequate-guide/ https://github.com/getify/Functional-Light-JS https://medium.com/@lunde.andrews/easing-into-functional-programming-in-javascript-30056bcc49a9 https://fp-bingotron.ian-thomas.net/ http://www.tomharding.me/ https://github.com/fantasyland/fantasy-land https://staltz.com/is-your-javascript-function-actually-pure.html https://egghead.io/courses/quickly-transform-data-with-transducers https://egghead.io/courses/professor-frisby-introduces-composable-functional-javascript https://www.youtube.com/watch?v=moAfgDFVLUs