Demystify Functional Programming in Swift

Trying to explain Functional Programming core concepts stripping away category theory (but with a lot of respect!) and apply them to Swift.

Transcript

1. DEMYSTIFY FUNCTIONAL PROGRAMMING IN (OR TRYING TO … ) ENNIO MASI SENIOR IOS DEV @ YOOX NET-A-PORTER
2. IN COMPUTER SCIENCE, FP IS A PROGRAMMING PARADIGM - A STYLE OF BUILDING THE STRUCTURE AND ELEMENTS OF COMPUTER PROGRAMS - THAT TREATS COMPUTATION AS THE EVALUATION OF MATHEMATICAL FUNCTIONS AND AVOIDS CHANGING - STATE AND MUTABLE DATA. IN COMPUTER SCIENCE, FP IS A PROGRAMMING PARADIGM - A STYLE OF BUILDING THE STRUCTURE AND ELEMENTS OF COMPUTER PROGRAMS - THAT TREATS COMPUTATION AS THE EVALUATION OF MATHEMATICAL FUNCTIONS AND AVOIDS CHANGING - STATE AND MUTABLE DATA. FUNCTIONAL PROGRAMMING IN COMPUTER SCIENCE, FP IS A PROGRAMMING PARADIGM - A STYLE OF BUILDING THE STRUCTURE AND ELEMENTS OF COMPUTER PROGRAMS - THAT TREATS COMPUTATION AS THE EVALUATION OF MATHEMATICAL FUNCTIONS AND AVOIDS CHANGING - STATE AND MUTABLE DATA. IN COMPUTER SCIENCE, FP IS A PROGRAMMING PARADIGM - A STYLE OF BUILDING THE STRUCTURE AND ELEMENTS OF COMPUTER PROGRAMS - THAT TREATS COMPUTATION AS THE EVALUATION OF MATHEMATICAL FUNCTIONS AND AVOIDS CHANGING - STATE AND MUTABLE DATA. Someone on Wikipedia
3. FP HAS ITS ORIGINS IN LAMBDA CALCULUS, A FORMAL SYSTEM DEVELOPED IN THE 1930S TO INVESTIGATE COMPUTABILITY, THE ENTSCHEIDUNGSPROBLEM, FUNCTION DEFINITION, FUNCTION APPLICATION, AND RECURSION. MANY FUNCTIONAL PROGRAMMING LANGUAGES CAN BE VIEWED AS ELABORATIONS ON THE LAMBDA CALCULUS. Someone else on Wikipedia FUNCTIONAL PROGRAMMING FP HAS ITS ORIGINS IN LAMBDA CALCULUS, A FORMAL SYSTEM DEVELOPED IN THE 1930S TO INVESTIGATE COMPUTABILITY, THE ENTSCHEIDUNGSPROBLEM, FUNCTION DEFINITION, FUNCTION APPLICATION, AND RECURSION. MANY FUNCTIONAL PROGRAMMING LANGUAGES CAN BE VIEWED AS ELABORATIONS ON THE LAMBDA CALCULUS. FP HAS ITS ORIGINS IN LAMBDA CALCULUS, A FORMAL SYSTEM DEVELOPED IN THE 1930S TO INVESTIGATE COMPUTABILITY, THE ENTSCHEIDUNGSPROBLEM, FUNCTION DEFINITION, FUNCTION APPLICATION, AND RECURSION. MANY FUNCTIONAL PROGRAMMING LANGUAGES CAN BE VIEWED AS ELABORATIONS ON THE LAMBDA CALCULUS. FP HAS ITS ORIGINS IN LAMBDA CALCULUS, A FORMAL SYSTEM DEVELOPED IN THE 1930S TO INVESTIGATE COMPUTABILITY, THE ENTSCHEIDUNGSPROBLEM, FUNCTION DEFINITION, FUNCTION APPLICATION, AND RECURSION. MANY FUNCTIONAL PROGRAMMING LANGUAGES CAN BE VIEWED AS ELABORATIONS ON THE LAMBDA CALCULUS.
4. FOUNDATIONS FP IS BASED ON CATEGORY THEORY WHICH IS REALLY COMPLEX
5. FUNCTIONAL PROGRAMMING (HATERS)
6. FUNCTIONAL PROGRAMMING (LOVERS)
7. FOUNDATIONS START
8. FOUNDATIONS FP IS AN APPROACH BASED ON FUNCTION CALLS F(X) —> Y
9. FOUNDATIONS FP IS AN APPROACH BASED ON FUNCTION CALLS OOP FP Single Responsability functions Open Closed Principle functions Dependecy Inversion functions Factory pattern functions … …
10. FOUNDATIONS F(X) = Y ▸ Write predictable functions FP IS AN APPROACH BASED ON FUNCTION CALLS ▸ Code easier to test ▸ Thread-safe codebase ▸ Functions chaining
11. FOUNDATIONS FP IS AN APPROACH BASED ON FUNCTION CALLS FP IS AN APPROACH BASED ON PURE FUNCTION CALLS
12. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS currentDate 20/11/2018 INPUT tellMeTheTruth(..) ? OUTPUT
13. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS currentDate 20/11/2018 INPUT tellMeTheTruth(..) false OUTPUT current date 21/11/2018
14. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS currentDate 20/11/2018 INPUT migrationStatus() true OUTPUT current date 19/11/2018
15. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS NOT PURE NO SIDE EFFECTS, TESTABLE, THREAD SAFE PURE
16. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS NOT PURE NO SIDE EFFECTS, TESTABLE, THREAD SAFE PURE
17. FOUNDATIONS F(X) = Y FP IS AN APPROACH BASED ON PURE FUNCTION CALLS NOT PURE NO SIDE EFFECTS, TESTABLE, THREAD SAFE PURE
18. FOUNDATIONS FP IS AN APPROACH BASED ON FUNCTION CALLS FP IS AN APPROACH BASED ON PURE FUNCTION CALLS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS
19. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS f(2) —> 2 * 3 = 6 g(6) —> 6 * 6 = 36 G(F(A)) = B g(f(2)) ➡ f(2) = 6 ➡ g(6) = 36
20. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS FUNCTIONS ARE FIRST CLASS CITIZENS HIGH ORDER FUNCTIONS SWIFT SUPPORTS FP
21. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS COMPOSITION F G A B C A C F G ⏭
22. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS COMPOSITION
23. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS F: A —>B G: B —>C F: INT —>INT G: INT —>INT F: INT —>INT G: INT —>INT H: INT —>STR
24. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS
25. FOUNDATIONS FP IS AN APPROACH BASED ON COMPOSITION OF PURE FUNCTION CALLS ▸ Write predictable functions ▸ Code easier to test ▸ Thread-safe codebase ▸ Features chaining
26. FOUNDATIONS: CURRYING CURRYING IS A WAY TO BREAKDOWN FUNCTIONS COMPLEXITY $ ▸ A curried function is executed only when all the parameters are set F(X, Y) —> Z ▸ Think to a function with N parameters as a function with N times 1 parameter F(X)(Y) —> Z
27. FOUNDATIONS: IMMUTABILITY
28. FOUNDATIONS: IMMUTABILITY IMPERATIVE VS FP S + DATA[I] IS “ILLEGAL” IN FP PURE FUNCTIONS MUST BE STATELESS
29. FOUNDATIONS: IMMUTABILITY OOP (IMPERATIVE) VS FP TAIL RECURSION IS NOT OPTIMISED IN SWIFT TAIL RECURSION SWIFT PARTIALLY SUPPORTS FP
30. FOUNDATIONS: IMMUTABILITY ▸ Thread-safe ADVANTAGES OF IMMUTABILITY ▸ Chaining of functions ▸ Predictable outputs
31. FOUNDATIONS: IMMUTABILITY ▸ Complex code base DISADVANTAGES OF IMMUTABILITY ▸ Performances
32. “A monad is just a monoid in the category of endofunctors” Someone on Internet FOUNDATIONS: FUNCTORS & MONADS
34. FOUNDATIONS: FUNCTORS & MONADS SWIFT OPTIONAL OPTIONAL IS A “CONTEXT” THAT CAN INCLUDE A VALUE OR NOT
35. FOUNDATIONS: FUNCTORS & MONADS FUNCTORS ▸ SINCE OPTIONAL IS A “CONTEXT”, WE NEED A WAY TO EXTRACT THE POSSIBLE VALUE FROM IT ▸ MAP
36. FOUNDATIONS: FUNCTORS & MONADS FUNCTORS ▸ SINCE OPTIONAL IS A “CONTEXT”, WE NEED A WAY TO EXTRACT THE POSSIBLE VALUE FROM IT ▸ MAP [<$>, <!>] OPTIONAL MAP VALUE OR NONE
37. FOUNDATIONS: FUNCTORS & MONADS FUNCTORS OPTIONAL MAP VALUE OR NONE A FUNCTOR IS A TYPE THAT CONTAINS A VALUE AND PROVIDES A MAP FUNCTION AS INTERFACE FUNCTOR MAP VALUE OR NONE HINT: OPTIONAL IS A FUNCTOR FP
38. FOUNDATIONS: FUNCTORS & MONADS FUNCTORS A FUNCTOR IS A TYPE THAT CONTAINS A VALUE AND PROVIDES A MAP FUNCTION AS INTERFACE HINT: OPTIONAL IS A FUNCTOR ▸ Identity Law ▸ Composition Law
39. FOUNDATIONS: FUNCTORS & MONADS MONADS A MONAD IS JUST A MONOID IN THE BLA BLA BLA … ▸ Well a monad is just a type on which we can apply flatMap (bind) FUNCTIONS CHAINING (ON VALUES) HINT: OPTIONAL IS A MONAD $ ▸ flatMap [>>=]
40. FOUNDATIONS: FEATURES CHAINING MONADS IN PRACTICE Well a monad is just a type on which we can apply flatMap (bind)
41. FOUNDATIONS: FEATURES CHAINING MONADS
42. FOUNDATIONS: FEATURES CHAINING string f1 f2 f Out Monad String bool bool bool error error error error bind return return
43. FOUNDATIONS: FEATURES CHAINING string f1 f2 f Out Monad bool bool bool bool error error error error bind return return FEATURES CHAINING (ON VALUES) ERROR MANAGEMENT VS
44. PLAYGROUND TIME https://github.com/ennioma/FPTalk-Playground