Swift Functional Programming

Overview of the basics of Functional Programming using the Swift programming language. Presented at the Functional Programming Miniconf at Linux.conf.au 2016, in Geelong.

Transcript

1. Swift Functional Programming @parisba
5. Agenda • What is Swift • Why bother? • Installing Swift • Playgrounds/REPL • Functional Programming Fundamentals • Swift Functional Programming
6. This is mostly a “how Swift does it” talk
7. A quick overview. Not all-inclusive.
8. Swift?! • Similar to Rust, Perl 6, and a bunch of other languages… • Another trendy, hip, cool, modern programming language… • Actually pretty good…
9. Why does Swift matter?
10. Swift is open source. swift.org
11. Swift is easy to teach.
12. iOS.
13. http://blog.appannie.com/app-annie-2015-retrospective/ Annual App Downloads, 2013 - 2015
14. http://blog.appannie.com/app-annie-2015-retrospective/ Annual App Revenue, 2013 - 2015
16. let = ["","",""] for in { print() }
17. Swift is not really a functional language
18. Nothing like a pure functional language.
19. Ideals of functional programming are important
20. Installing Swift
21. Available on Linux and OS X (OS X installation: just download Xcode)
22. Binaries available for Ubuntu
23. $ sudo apt-get install clang libicu-dev Download a binary from https://swift.org/download/#linux; extract it $ tar xzf swift-<VERSION>-<PLATFORM>.tar.gz $ export PATH=/path/to/usr/bin:"${PATH}" This creates a usr/ directory; add it to your path: Swift is now installed! Download the pre-requisites:
24. Useful Swifty Things
25. Playgrounds
26. $ swift Welcome to Apple Swift version 2.1.1 (swiftlang-700.1.101.15 clang-700.1.81). Type :help for assistance. 1> let text = "Don t worry if you are not computer" text: String = "Don t worry if you are not computer" 2> text.uppercaseString $R0: String = "DON T WORRY IF YOU ARE NOT COMPUTER" 3>
27. What does functional programming mean?
28. Functions
29. First-class functions
30. Higher-order functions
31. Pure functions
32. Pure functions have no side effects.
33. No I/O, no changing outside state.
34. Why does functional programming matter?
35. © GDC CC-BY 2.0
36. –John Carmack “No matter what language you work in, programming in a functional style provides benefits. You should do it whenever it is convenient, and you should think hard about the decision when it isn't convenient.”
37. yeah ok but WHY
38. “Pure functions have a lot of nice properties.”
39. • Thread safety • Reusability • Testability • Understandability • Maintainability
40. Important Language Support
41. A really nice type system.
42. First-class functions. See also: lambda calculus, Haskell, OCaml, Scala, and so on.
43. func add(num1: Int, _ num2 : Int) -> Int { return num1 + num2 }
44. func add(num1: Int, _ num2 : Int) -> Int { return num1 + num2 } var addNumbers : (Int,Int) -> Int
45. func add(num1: Int, _ num2 : Int) -> Int { return num1 + num2 } var addNumbers : (Int,Int) -> Int addNumbers = add
46. func add(num1: Int, _ num2 : Int) -> Int { return num1 + num2 } var addNumbers : (Int,Int) -> Int addNumbers = add addNumbers(1,2)
47. Closures
48. Inline first-class functions
49. var add = { (num1 : Int, num2 : Int) -> Int in return num1 + num2 }
50. Swift will infer as much type info as it can
51. var add = { (num1 : Int, num2 : Int) -> Int in return num1 + num2 }
52. var add = { (num1 : Int, num2 : Int) -> Int in return num1 + num2 }
53. var add = { (num1 : Int, num2 : Int) -> Int in return num1 + num2 }
54. var add : (Int,Int) -> Int add = { $0 + $1 }
55. var add : (Int,Int) -> Int add = (+)
56. Value capturing
57. typealias Adder = (Int) -> Int
58. typealias Adder = (Int) -> Int func makeAdder(number: Int) -> Adder { return { $0 + number } }
59. typealias Adder = (Int) -> Int func makeAdder(number: Int) -> Adder { return { $0 + number } } let addTwo = makeAdder(2)
60. typealias Adder = (Int) -> Int func makeAdder(number: Int) -> Adder { return { $0 + number } } let addTwo = makeAdder(2) addTwo(5) // 7
61. First-class functions means we get higher-order functions!
62. typealias TwoIntegerFunction = (Int,Int) -> Int
63. typealias TwoIntegerFunction = (Int,Int) -> Int func applyOperationToNumbers(num1 : Int, _ num2 : Int, operation: TwoIntegerFunction) -> Int { return operation(num1, num2) }
64. typealias TwoIntegerFunction = (Int,Int) -> Int func applyOperationToNumbers(num1 : Int, _ num2 : Int, operation: TwoIntegerFunction) -> Int { return operation(num1, num2) } let add : TwoIntegerFunction = { $0 + $1 }
65. typealias TwoIntegerFunction = (Int,Int) -> Int func applyOperationToNumbers(num1 : Int, _ num2 : Int, operation: TwoIntegerFunction) -> Int { return operation(num1, num2) } let add : TwoIntegerFunction = { $0 + $1 } applyOperationToNumbers(2, 3, operation: add)
66. typealias TwoIntegerFunction = (Int,Int) -> Int func applyOperationToNumbers(num1 : Int, _ num2 : Int, operation: TwoIntegerFunction) -> Int { return operation(num1, num2) } let add : TwoIntegerFunction = { $0 + $1 } applyOperationToNumbers(2, 3, operation: add) applyOperationToNumbers(2, 3, operation: +)
67. Optionals
68. In Swift, variables are never allowed to be nil, unless they’re Optionals.
69. var text = "As you might know, I am a full time Internet" text.uppercaseString // "AS YOU MIGHT KNOW, I AM A FULL TIME INTERNET"
70. let textFromDisk = loadTextFromDisk() textFromDisk.uppercaseString // Error!!
71. Very similar to Haskell’s Maybe
72. let textFromDisk = loadTextFromDisk() textFromDisk?.uppercaseString // "EVERYTHING HAPPENS SO MUCH"
73. Some Contrived Examples using Swift
74. func incrementArray(theArray: [Int]) -> [Int] { var result: [Int] = [] for item in theArray { result.append(item+1) } return result }
75. func doubleArray(theArray: [Int]) -> [Int] { var result: [Int] = [] for item in theArray { result.append(item*2) } return result }
76. typealias TransformFunction = Int -> Int func manipulateArray(theArray: [Int], transform: TransformFunction) -> [Int] { var result: [Int] = [] for item in theArray { result.append(transform(item)) } return result }
77. func doubleArray(xs: [Int]) -> [Int] { return manipulateArray(xs, transform:{ $0*2 }) }
78. Limitations…
79. [ ] , , , Int Int Int Int [ ] , , , Int Int Int Int
80. [ ] , , , Int Int Int Int [ ] , , , ? Bool Bool Bool Bool
81. Writing duplicate versions sucks
82. Generics!
83. func manipulateArray(theArray: [Int], transform: TransformFunction) -> [Int] { var result: [Int] = [] for item in theArray { result.append(transform(item)) } return result }
84. func map<T>(xs: [Int], transform: Int->T) -> [T] { var result: [T] = [] for x in xs { result.append(transform(x)) } return result }
85. func map<T>(xs: [Int], transform: Int->T) -> [T] { var result: [T] = [] for x in xs { result.append(transform(x)) } return result }
86. But we can take it further…
87. func map<Element, T>(xs: [Element], transform: Element->T) -> [T] { var result: [T] = [] for x in xs { result.append(transform(x)) } return result }
88. let doubledArray = map([1,2,3,4], transform: { $0 * 2} )
89. extension Array { func map<T>(transform: (Element) -> T) -> [T] { var result: [T] = [] for x in self { result.append(transform(x)) } return result } }
90. [1,2,3,4].map({ $0 * 2 })
91. Map actually comes with Swift Hopefully you were expecting me to say that… … the point is, there’s no secrets to Map!
92. Composing functions
93. 10 11 +1 ×2
94. 5 10 11 +1 ×2
95. 5 10 11 +1 ×2
96. 5 10 11 +1 ×2
97. 5 10 11 +1 ×2
98. ×2 +1
99. 11 ×2 +1
100. 5 11 ×2 +1
101. 5 11 ×2 +1
102. // Compose a function from two functions func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T { // Return a new function that calls them both return { funcB(funcA($0)) } }
103. // Compose a function from two functions func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T { // Return a new function that calls them both return { funcB(funcA($0)) } } // Two dumb lil functions let double = { $0 * 2 } let addOne = { $0 + 1 }
104. // Compose a function from two functions func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T { // Return a new function that calls them both return { funcB(funcA($0)) } } // Two dumb lil functions let double = { $0 * 2 } let addOne = { $0 + 1 } // Compose 'em! let doubleAndAddOne = compose(double, addOne)
105. // Compose a function from two functions func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T { // Return a new function that calls them both return { funcB(funcA($0)) } } // Two dumb lil functions let double = { $0 * 2 } let addOne = { $0 + 1 } // Compose 'em! let doubleAndAddOne = compose(double, addOne) doubleAndAddOne(5)
106. Limitations!
107. func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T These have to be the same type, for no good reason!
108. Is Even? Flip Boolean Bool Int Bool Bool
109. No Is Even? Flip Boolean
110. 4 No Is Even? Flip Boolean
111. 4 No Is Even? Flip Boolean
112. func compose<T>(funcA: T->T, _ funcB: T->T) -> T->T { return { funcB(funcA($0)) } }
113. func compose<T,U,V>(funcA: T->U, _ funcB: U->V) -> T->V { return { funcB(funcA($0)) } }
114. func compose<T,U,V>(funcA: T->U, _ funcB: U->V) -> T->V { return { funcB(funcA($0)) } } let isEven = { $0 % 2 == 0 } // Int -> Bool let flipBool = { !$0 } // Bool -> Bool let isNotEven = compose(isEven, flipBool) // Int -> Bool isNotEven(4) // false
115. Third-party Stuff
116. Swiftz https://github.com/typelift/swiftz
117. Better types and tools for FP
118. import struct Swiftz.List // Cycles a finite list of numbers into an infinite list. let finite : List<UInt> = [1, 2, 3, 4, 5] let infiniteCycle = finite.cycle() // Lists also support the standard map, filter, and reduce operators. let l : List<Int> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] let twoToEleven = l.map(+1) // [2, 3, 4, 5, 6, 7, 8, 9, 10, 11] let even = l.filter((==0) • (%2)) // [2, 4, 6, 8, 10] let sum = l.reduce(curry(+), initial: 0) // 55 // Plus a few more. let partialSums = l.scanl(curry(+), initial: 0) // [0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55] let firstHalf = l.take(5) // [1, 2, 3, 4, 5] let lastHalf = l.drop(5) // [6, 7, 8, 9, 10]
119. Promissum https://github.com/tomlokhorst/Promissum
120. Dollar.swift dollarswift.org
121. Result https://github.com/antitypical/Result
122. Learning more • Learn You a Haskell for Great Good! • Pearls of Functional Algorithm Design • Programming in Haskell (Hutton) • Apple’s Swift Book(s) • IBM Swift Resources: https://developer.ibm.com/swift/
123. Thank you @parisba / http://www.secretlab.com.au