Kristian Andersen ksmandersen

[fit] Functional Programming in

[fit] Swift

Chris Eidhof - objc.io - June 28, Minsk

NOTE (2022-07-09): Xcode finally added this functionality in Xcode 14, please see release notes here:

New Features in Xcode 14 Beta 3
When editing code, the Edit > Duplicate menu item and its corresponding keyboard shortcut now duplicate the selected text — or the line that currently contains the insertion point, if no text is selected. (8614499) (FB5618491)

Xcode line duplicate

Bind keys to duplicate lines in Xcode

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

	#!/bin/bash
	#
	# convert-video.sh
	#
	# Copyright (c) 2013-2014 Don Melton
	#

	about() {
	cat <<EOF
	$program 2.0 of December 3, 2014

	// Thanks to http://www.labs.saachitech.com/2012/10/23/pdf-generation-using-uiprintpagerenderer
	// Note: including images in the HTML won't work, see here:
	// https://github.com/nyg/HTMLWithImagesToPDF

	import UIKit

	// 1. Create a print formatter

	let html = "<b>Hello <i>World!</i></b>"
	let fmt = UIMarkupTextPrintFormatter(markupText: html)

	import Darwin

	extension Int {
	static func random() -> Int {
	return Int(arc4random())
	}

	static func random(range: Range<Int>) -> Int {
	return Int(arc4random_uniform(UInt32(range.endIndex - range.startIndex))) + range.startIndex
	}

	import Random

	random(0 ..< 10) // Int
	random(1 ... 1000_000) // Int
	random(-1000_000 ... 1000_000) // Int
	random(Int.min ... Int.max) // Int

	randomMax(UInt64.max) // UInt64
	random(0 ... UInt64.max) // UInt64
	random(1 ... UInt(10)) // UInt

	// NOTE: This is now rolled up in a package and supports more scenarios: https://github.com/dsherret/using-statement

	interface IDisposable {
	dispose();
	}

	function using<T extends IDisposable>(resource: T, func: (resource: T) => void) {
	try {
	func(resource);
	} finally {

	struct Coordinator {
	let window: UIWindow
	let navCtrl: UINavigationController?

	func start() {
	presentWelcomeScreen()
	}

	private func presentWelcomeScreen() {
	let vc = WelcomeScreenViewController() // Instanciate from code, XIB, Storyboard, whatever your jam is

	import Foundation

	/**
	Coordinators are a design pattern that encourages decoupling view controllers such that they know as little as possible
	about how they are presented, and don’t directly manipulate data or present other view controllers. Coordinators can be
	“nested” such that child coordinators encapsulate different flows and present any from becoming too large.

	- https://vimeo.com/144116310
	- http://khanlou.com/2015/10/coordinators-redux/
	- http://khanlou.com/2015/01/the-coordinator/