Funcitonal Swift Conference: The Functional Way

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Talk about Functional Swift presented at the Functional Swift Conference http://2014.funswiftconf.com/

Published in: Software, Engineering, Technology

Funcitonal Swift Conference: The Functional Way

  1. THE FUNCTIONAL WAY @NATASHATHEROBOT
  2. "functional programming is a programming paradigm... that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data." Wikipedia
  3. "A mathematical function is a function that when you give it the same argument, it will give you the same result" - Edx FP101x
  4. ▸ computation as the evaluation of mathematical functions ▸ avoid changing state ▸ avoid mutable data
  5. NO SIDE EFFECTS
  6. let numbers = Array(1...10) var total = 0 func addNumbers() { for number in numbers { total += number } }
  7. addNumbers() total // 55 addNumbers() total // 110 addNumbers() total // 165
  8. let myNumbers = Array(1...10) var total = addNumbers(myNumbers) func addNumbers(numbers: [Int]) -> Int { // can also be written shorthand as // numbers.reduce(0,+) return numbers.reduce(0) { (sum, number) in sum + number } }
  9. total = addNumbers(myNumbers) // 55 total = addNumbers(myNumbers) // 55 total = addNumbers(myNumbers) // 55
  10. import Foundation class Gift { let recipient: String let item: String let budget: NSDecimalNumber let status: Status enum Status: String { case Purchased = "Purchased" case Wrapped = "Wrapped" case Delivered = "Delivered" } init(recipient: String, item: String, budget: NSDecimalNumber, status: Status) { self.recipient = recipient self.item = item self.budget = budget self.status = status } }
  11. extension Gift { func todo() -> String { switch status { case .Purchased: return "Wrap it!" case .Wrapped: return "Mail it!" case .Delivered: return "Relax and drink some eggnog :)" } } }
  12. extension Gift { func todo(fromStatus status: Status) -> String { switch status { case .Purchased: return "Wrap it!" case .Wrapped: return "Mail it!" case .Delivered: return "Relax and drink some eggnog :)" } } }
  13. class GiftTests: XCTestCase { func testTodo_Purchased() { let gift = Gift( recipient: "My Cousin Julie, item: "GoldieBlox", budget: NSDecimalNumber(double: 20.00), status: .Purchased) XCTAssertEqual(gift.todo(), "Wrap it!") } func testTodo_Wrapped() { let gift = Gift( recipient: "My Cousin Julie", item: "GoldieBlox", budget: NSDecimalNumber(double: 20.00), status: .Wrapped) XCTAssertEqual(gift.todo(), "Mail it!") } func testTodo_Delivered() { let gift = Gift( recipient: "My Cousin Julie", item: "GoldieBlox", budget: NSDecimalNumber(double: 20.00), status: .Delivered) XCTAssertEqual(gift.todo(), "Relax and drink some eggnog :)") } }
  14. import XCTest class GiftTests: XCTestCase { let gift = Gift( recipient: "My Cousin Tommy", item: "Choo Choo Train", budget: NSDecimalNumber(double: 20.00), status: .Purchased) func testTodo_Purchased() { XCTAssertEqual(gift.todo(fromStatus: .Purchased), "Wrap it!") } func testTodo_Wrapped() { XCTAssertEqual(gift.todo(fromStatus: .Wrapped), "Mail it!") } func testTodo_Delivered() { XCTAssertEqual(gift.todo(fromStatus: .Delivered), "Relax and drink some eggnog :)") } }
  15. import XCTest class GiftTests: XCTestCase { func testTodo_Purchased() { XCTAssertEqual(Gift.todo(fromStatus: .Purchased), "Wrap it!") } func testTodo_Wrapped() { XCTAssertEqual(Gift.todo(fromStatus: .Wrapped), "Mail it!") } func testTodo_Delivered() { XCTAssertEqual(Gift.todo(fromStatus: .Delivered), "Relax and drink some eggnog :)") } }
  16. VALUE TYPES
  17. "Almost all types in Swift are value types, including arrays, dictionaries, numbers, booleans, tuples, and enums. Classes are the exception rather than the rule." - Functional Swift Book
  18. NSError *err = nil; CGFloat result = [MYArithmetic divide:2.5 by:3.0 error:&err]; if (err) { NSLog(@"%@", err) } else { [MYArithmetic doSomethingWithResult:result] } @nomothetis
  19. enum Result { case Success(AnyObject) case Failure(NSError) } @nomothetis
  20. let result = MYArithmetic.divide(2.5, by:3) switch result { case Success(let quotient): doSomethingWithResult(quotient) case Failure(let error): handleError(error) } @nomothetis
  21. http://nomothetis.svbtle.com/error-handling-in-swift
  22. CURRYING
  23. func add(x: Int, y: Int) -> Int { return x + y } add(2, 3) // 5
  24. func add(x: Int) -> Int -> Int { return { y in return x + y } } let partialAdd = add(2) // let addFunc: (Int -> Int) let sum = partialAdd(3) // 5 let arr = [1,2,3] let incrementBy2 = arr.map(partialAdd) // [3,4,5] add(6)(4) // 10
  25. func add(#x: Int)(y: Int) -> Int { return x + y } add(x: 2)(y: 3) // 5
  26. struct Logger { /// Level of log message to aid in the filtering of logs enum Level: Int, Printable { /// Messages intended only for debug mode case Debug = 3 /// Messages intended to warn of potential errors case Warn = 2 /// Critical error messages case Error = 1 /// Log level to turn off all logging case None = 0 var description: String { switch(self) { case .Debug: return "Debug" case .Warn: return "Warning" case .Error: return "Error" case .None: return "" } } } } @drewag
  27. extension Logger { /// What is the max level to be logged /// /// Any logs under the given log level will be ignored static var logLevel: Level = .Warn /// Log a message to the console static func log (#level: Level) (name: String) (message: String) -> String { if level.rawValue <= Logger.logLevel.rawValue { return "(level.description): (name) - (message)" } return "" } } @drewag
  28. Logger.log(level: .Debug)(name: "MyFunction")(message: "Is this being called?") // Debug: MyFunction - Is this being called?
  29. extension Logger { /// Logger for debug messages static var debug = Logger.log(level: .Debug) // static var debug: (name: String) -> (message: String) -> String /// Logger for warnings static var warn = Logger.log(level: .Warn) /// Logger for errors static var error = Logger.log(level: .Error) } @drewag
  30. Logger.logLevel = .Debug func myFunctionToDebug() { var x = 5 // do something to x Logger.debug(name: "myFunctionToDebug")(message: "x: (x)") } myFunctionToDebug() // Prints: "Debug: myFunctionToDebug - x: 10" @drewag
  31. func myFunctionToDebug() { var x = 5 var y = 3 // do something to x // do something to y let debugMyFunction = Logger.debug(name: "myFunctionToDebug") debugMyFunction(message: "x: (x)") debugMyFunction(message: "y: (y)") } myFunctionToDebug() // Prints: "Debug: myFunctionToDebug - x: 10" // Prints: "Debug: myFunctionToDebug - y: 13"
  32. http://drewag.me/posts/practical-use-for-curried-functions-in-swift
  33. TYPE-DRIVEN DESIGN
  34. func credits(account: Account) -> Int { // ask data source for account credits return credits } @FunctionalSwift
  35. typealias Credits = Int func credits(account: Account) -> Credits { // ask data source for amount of credits return amount } @FunctionalSwift
  36. "One important lesson I've learned is that designing the right types for your problem is a great way to help the compiler debug your program." - @wouterswierstra
  37. struct Credits { let amount: Int } func credits(account: Account) -> Credits { // ask data source for amount of credits return Credits(amount: amount) } @FunctionalSwift
  38. let myCredits = credits(myAccount) myCredits + 1 // ERROR // Cannot invoke '+' with an argument of type // '(Credit, IntegerLiteralConvertable)'
  39. http://www.objc.io/snippets/8.html http://www.swiftcast.tv/articles/the-design-of-types
  40. RESOURCES ▸ Functional Swift Book ▸ Edx FP101x ▸ Functional Snippets ▸ An Introduction to Haskell - Skills Matter ▸ swiftnews.curated.co
  41. QUESTIONS? @NATASHATHEROBOT

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