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![• homoiconicity == less syntax to learn
• turn all your fancy { } and [ ] into ( ) and
you get LISP again!
• because I've never used http://
goshdarnblocksyntax.com](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-13-2048.jpg)
![Inmutability: a clear example
- (void)version1 {
NSString *myString = @"iOSDevUK 16";
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringAllGood:myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringReallyStupidBug:myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringEvilBug:&myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
}
- (void)printAStringAllGood:(NSString *)aString {
NSLog(@"Printing: %@", aString);
}
- (void)printAStringReallyStupidBug:(NSString *)aString {
aString = nil; // stupid mistake
NSLog(@"Printing: %@", aString);
}
- (void)printAStringEvilBug:(NSString **)aString {
*aString = @"HaHa";
NSLog(@"Printing: %@", *aString);
}](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-30-2048.jpg)
![Map example
let basket = ["!", """, "#", "$", "%"]
basket.map { (e: String) -> String in
return "&" + e
}](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-37-2048.jpg)
![Filter example
• "I only want Apples"
let basket = ["!", """, "#", "$", "%", "&"]
let newBasket = basket.filter { $0 == "!" || $0 == "&"
}](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-40-2048.jpg)
![Reduce example
let numbers = [1, 2, 3, 4, 5, 6]
numbers.reduce(0, combine: +) --> 21](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-42-2048.jpg)
![Flatmap example
// how do you add 2 to all the numbers in this array?
let fa2 = [[1,2],[3],[4,5,6]]
let fa2m = fa2.flatMap({$0}).map({$0 + 2})
fa2m](https://image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-44-2048.jpg)
![• homoiconicity == less syntax to learn
• turn all your fancy { } and [ ] into ( ) and
you get LISP again!
• because I've never used http://
goshdarnblocksyntax.com](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-13-2048.jpg)
![Inmutability: a clear example
- (void)version1 {
NSString *myString = @"iOSDevUK 16";
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringAllGood:myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringReallyStupidBug:myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16
[self printAStringEvilBug:&myString];
NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16
}
- (void)printAStringAllGood:(NSString *)aString {
NSLog(@"Printing: %@", aString);
}
- (void)printAStringReallyStupidBug:(NSString *)aString {
aString = nil; // stupid mistake
NSLog(@"Printing: %@", aString);
}
- (void)printAStringEvilBug:(NSString **)aString {
*aString = @"HaHa";
NSLog(@"Printing: %@", *aString);
}](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-30-2048.jpg)
![Map example
let basket = ["!", """, "#", "$", "%"]
basket.map { (e: String) -> String in
return "&" + e
}](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-37-2048.jpg)
![Filter example
• "I only want Apples"
let basket = ["!", """, "#", "$", "%", "&"]
let newBasket = basket.filter { $0 == "!" || $0 == "&"
}](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-40-2048.jpg)
![Reduce example
let numbers = [1, 2, 3, 4, 5, 6]
numbers.reduce(0, combine: +) --> 21](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-42-2048.jpg)
![Flatmap example
// how do you add 2 to all the numbers in this array?
let fa2 = [[1,2],[3],[4,5,6]]
let fa2m = fa2.flatMap({$0}).map({$0 + 2})
fa2m](https://crownmelresort.com/image.slidesharecdn.com/fp-for-busy-oop-160910092441/75/Functional-Programming-for-Busy-Object-Oriented-Programmers-44-2048.jpg)
Uploaded byDiego Freniche Brito
Functional Programming for Busy Object Oriented Programmers
This document provides an overview of the speaker's experience with programming languages and introduction to functional programming concepts. It discusses that the speaker was initially taught imperative languages like BASIC and C++ in college but was also exposed to Lisp, an early functional language. Several core FP concepts pioneered by Lisp like recursion, higher-order functions, and homoiconicity are explained. The document advocates using some FP principles like immutability and map/filter/reduce in other languages to gain benefits while not needing to be a "pure" functional programmer.
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Functional Programming for Busy Object Oriented Programmers
- 1. Functional Programming for busy OOP Nowwith obligatory kitten!
- 2. Hello, World! • DiegoFreniche 1 • @dfreniche • 100% remote dev (iOS / Android) • writing new bugs @ Mobile Jazz 1 CV: git clone http://www.github.com/dfreniche/cv
- 3. BASIC days • WhatI've already learnt at iOSDevUK'16: • I'm a dinosaur • We're getting older • Nostalgia is in the air
- 5. GLORY days • selftaught PASCAL before starting College • just to find C was the language of choice • saw several languages: Ada, C, C++ • fell in love with C++ (pre-STL times...)
- 7. Wait, am Ian imperative programmer? • Cursed for life ! • Spoiled by BASIC, C++ • will never get a job in CS. Ever.
- 8. Well maybe Ican call myself a REAL OOP developer • this book is really hard to read • I mean, like really hard • that's only imperative++
- 9. Wait, I wastaught LISP in College • You know: • Lost In Stupid Parentheses • Lots of Irritating Superfluous Parentheses • ...
- 10. F.P.: a newthing, right? ! • invented in the late 50's (1958) • only ALGOL is older • derived from the Lambda Calculi (developed in the 30's)
- 11. A word (ortwo) on LISP • simplest syntax in ANY programming language • Code: (+ 3 2) • List of data: '("hello", "world")
- 12. A word (ortwo) on LISP • homoiconicity: "the structure of program code is represented faithfully and directly in a standard data structure" • we have direct access to the compiler's AST • Much power. So cool. Such compiler. Wow
- 13. • homoiconicity ==less syntax to learn • turn all your fancy { } and [ ] into ( ) and you get LISP again! • because I've never used http:// goshdarnblocksyntax.com
- 14. Eval: treat datalike code, code like data • Eval: treat data like code, code like data CL-USER> '(+ 3 4) (+ 3 4) CL-USER> (+ 3 4) 7 CL-USER> (eval '(+ 3 4)) 7 ! https://repl.it/languages/scheme
- 15. Ideas piooneered byLISP • tree data structures • automatic storage management • dynamic typing • conditionals • higher-order functions • recursion • the self-hosting compiler • REPL: Read Eval Print Loop interpreter
- 16. Greenspun's tenth rule2 Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp. 2 maybe the NSA, Santa Claus, Zuck and your peers who hate F.P.
- 17. F.P. is back! •Closures & High Order Funcions in Swift. Inmutability. Optionals. • Blocks in Objective-C to mimic Closures. • Scala • C# / F# • JavaScript?
- 18. Being a FunctionalLanguage vs. having Functional Constructs There's no accepted definition of functional programming language. _ If you define functional language as the language that supports first class functions and lambdas, then yes, JavaScript is a functional language.3 3 http://stackoverflow.com/questions/3962604/is-javascript-a-functional-programming-language
- 19. Functional Programming ... functionalprogramming is a programming paradigm ... that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It is a declarative programming paradigm,
- 20. Functional Programming ... theoutput value of a function depends only on the arguments that are input to the function, so calling a function f twice with the same value for an argument x will produce the same result f(x) each time eliminating side effects https://en.wikipedia.org/wiki/Functional_programming
- 22. All the talksI've been before • Me: "Hi, I'm Diego, need to lose some weight" • Someone at the Gym: "No problem, you can start doing this Arnold lift weigthing routines from his training to became Mister Olympia" • Me: !
- 23. All the talksI've been before • I know nothing about it, but want to learn! ☝ • Functors, Monads, Functional purity, etc. " • Talks like "Type Check Removal Using Lazy Interprocedural Code Versioning" #
- 24. Why you hateFP? • Functional programming is declarative • we were born as imperative programmers! • say what you want, not micromanage how to do it • you're already doing it! (hating) • SQL • CSS • Regular expressions
- 25. OK, Something practical,please?
- 26. Inmutability, avoiding state,don't shoot yourself in the foot • Value types and immutability • compiler can optimize your code ! • eats more memory " • also CPU (making all those copies) " • this can be optimized • optimizes programmer's time #
- 27. Inmutability • Diego's constantsdumb rule Declare everything as a constant, let compiler warn you when you're changing something. That's a variable. // Java: final everything final String s = ""; s = "other thing"; // nope // Swift let s: String = ""
- 28. Inmutability: nice toavoid mistakes - (void)printAStringReallyStupidBug:(NSString *)aString { aString = nil; // stupid mistake // really clever code // trust me, I know what I'm doing // in this 300 lines method NSLog(@"Printing: %@", aString); }
- 29. Inmutability func removeFromString( _s: inout String, Character c:Character) -> Int { var nRemoved = 0 while let ix = s.characters.index(of: c) { s.removeSubrange(ix...ix) nRemoved += 1 } return nRemoved }
- 30. Inmutability: a clearexample - (void)version1 { NSString *myString = @"iOSDevUK 16"; NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16 [self printAStringAllGood:myString]; NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16 NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16 [self printAStringReallyStupidBug:myString]; NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16 NSLog(@"myString BEFORE: %@", myString); // BEFORE: iOSDevUK 16 [self printAStringEvilBug:&myString]; NSLog(@"myString AFTER: %@", myString); // AFTER: iOSDevUK 16 } - (void)printAStringAllGood:(NSString *)aString { NSLog(@"Printing: %@", aString); } - (void)printAStringReallyStupidBug:(NSString *)aString { aString = nil; // stupid mistake NSLog(@"Printing: %@", aString); } - (void)printAStringEvilBug:(NSString **)aString { *aString = @"HaHa"; NSLog(@"Printing: %@", *aString); }
- 31. Inmutability lessons • learnto use debug breakpoints • change your code to call that function • we can use blocks, function pointers, Swift closures... • a little tradegy in that backward language NSString const *myString = @"iOSDevUK 16"; ⚠ Sending 'const NSString *__strong' to parameter of type 'NSString *' discards qualifiers
- 32. Inmutability: don't use++ var i = 0 print("( ++i )") • direct translation from assembler INC • does several things at once • hard to reason about • nice syntax !
- 33. Optionals are nota new thing • non-optionals are the new thing! class Person { var name: String // compiler ERROR: you can't fool me! }
- 34. Optionals are nota new thing class Politician: Hyena { // still compiler ERROR }
- 35. High order functions •Functions that take functions as parameters • Map, Filter, Reduce, Flatmap • Let's do something with these fruits
- 36. Map • "Do THISto every single element in the list" • add 1 to every element in this list • takes a function (add one) & a list • returns a list • with a basket of fruit: peel every fruit in this basket • think of SQL update
- 37. Map example let basket= ["!", """, "#", "$", "%"] basket.map { (e: String) -> String in return "&" + e }
- 38. Map Benefits • mapis a level of indirection • can be run in parallel (applying a function on element n doesn't depend on element n+1)
- 39. Filter • "I onlywant oranges from that basket" • SQL select WHERE clause
- 40. Filter example • "Ionly want Apples" let basket = ["!", """, "#", "$", "%", "&"] let newBasket = basket.filter { $0 == "!" || $0 == "&" }
- 41. Reduce • takes afunction (add) & a list • returns just one element • make multi-fruit juice • think of AVG function in SQL
- 42. Reduce example let numbers= [1, 2, 3, 4, 5, 6] numbers.reduce(0, combine: +) --> 21
- 43. Flatmap • Like map,but also "flattens" the list • some of the fruits in the basket are wrapped with paper
- 44. Flatmap example // howdo you add 2 to all the numbers in this array? let fa2 = [[1,2],[3],[4,5,6]] let fa2m = fa2.flatMap({$0}).map({$0 + 2}) fa2m
- 45. This is fromClean Coding... or not • Functions should be: • Small • Smaller than that • < 150 chars per line • < 20 lines
- 46. Inject all yourparameters • even if you're using properties from your own class • makes everything inmediately testable • no side effects: everything is clear when calling • you get your own Domain Specific Language to express your problem
- 47. So what? • youdon't need to be an athlete to run and be healthier • you don't need to be pure to benefit from some FP goodness
- 48. So what? • useinmutable structures where possible • in Java, for example, final everything • in Swift, prefer structs (value types) vs classes (reference types)
- 49. So what? • map/ filter / reduce helps sometimes • think of it as having SQL at your fingertips • not everything is a for loop
- 50. Use the bestof OOP + the best of FP. Nobody will ever know. 2 2 maybe the NSA, Santa Claus, Zuck and your peers who hate F.P.
- 51. Thanks! • No Trademarkswere hurt during the making of this talk. • all trademarks belong to their owners, so please don't sue me.
- 52. Additional reading • Areally good post on what F.P. is (with Swift examples!) http:// five.agency/functional-programming-in-swift/ • A parallel map implementation: http:// moreindirection.blogspot.com.es/2015/07/gcd-and-parallel- collections-in-swift.html