Roy Marmelstein marmelroy

Note: This is an older post that I did back when I thought I might have time to be a blogger. Oh I was oh so wrong. However, it has proven useful for some folks on stackoverflow. Thus I'm keeping it alive here on Gist.

One of my past projects dealt heavily with an open source Apple technology called HTTP Live Streaming. It’s an HTTP based streaming protocol that at its most fundamental level provides a way to stream video and audio from just about any server with nothing but a few free software tools provided by Apple**. However, it has a few additional features that I think make it a really exciting tool. Yet, I haven’t seen HTTP Live Streaming used very much. This is probably mainly due to the combination of a lack of good/clear documentation, and Apple’s Live Streaming Developer Tools being command line based also make the barrier to entry higher than many developers want to deal with.

The hope is to share my understanding of how to use this technology to:

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,

	#!/usr/bin/env swift

	#if os(Linux)
	import Glibc

	let sin_zero = (UInt8(0),UInt8(0),UInt8(0),UInt8(0),UInt8(0),UInt8(0),UInt8(0),UInt8(0))
	let sock_stream = Int32(SOCK_STREAM.rawValue)
	#else
	import Darwin.C

	//
	// SpinlockTestTests.swift
	// SpinlockTestTests
	//
	// Created by Peter Steinberger on 04/10/2016.
	// Copyright © 2016 PSPDFKit GmbH. All rights reserved.
	//

	import XCTest