const app = {
lines: document.getElementById('lines'),
textbox: createTextbox(),
lineTemplate: createLineTemplate(),

const socket = connect(

initial({ lines, uuid, charLimit }) {
app.uuid = uuid
app.charLimit = charLimit

added(line) {

removed(i) {

server.onclose = (ws) => {
if (ws.line) {
const i = lines.indexOf(ws.line)
lines.splice(i, 1)
server.sendToAll({ removed: i })

server.commands = {

begin(ws) {
const line = {
hash: ws.hash,
uuid: ws.uuid,
text: '',

ws.line = line
server.sendToAll({ added: line })

run() {
console.log(`Running on port ${this.port}`)

this.wss = new WebSocket.Server({
port: this.port,
verifyClient: this.verify.bind(this)

this.pruneInterval * 1000


Steven Degutis

Full-stack software developer for hire

Finite state machines

October 24, 2010

On Thursday, I did not write anything about that day in my apprenticeship because I was still learning about and trying to absorb the concepts of Finite State Machines (FSMs).

On Friday, I did not write anything because I was pooped. So here I am tonight writing about both days.

At first, the concept of a Finite State Machine was a little fuzzy. I sort of understood it, partially thanks to Eric’s drawings on some glass which helped. The basics of it, so far as I understand it, is that there is an object which contains a single “state”, a defined set of initial states and end states, events which trigger a transition from one state to another, and (optionally) actions to be performed at each transition.

The reason it’s called finite is because each state that could possibly arise in the state machine, and each transition between them, is entirely defined before the state machine is every run.

So, for example, one of those “choose-your-own-adventure” games (like Zork!) could represent a finite state machine. At each “turn”, you start at the initial state. Once you “take your turn”, the turn represents the event, which triggers an action (you die, find a treasure chest, encounter a monster, etc), and afterwards are moved to another state (dead, rich, hyperarousal, etc).

So that’s the basics of a state machine. My intentions were to use it to create a “markdown-like-language” parser for the Ruby Wiki I’m writing as a project designated by Eric. The language is simple right now, consisting only of emphasis, strong, and paragraph controls. Originally it was implemented as regular expressions (which Skim helped me with, thanks Skim!) but that was a bit fragile, plus it evaded the whole learning-FSM thing, which will undoubtedly come in handy later.

Initially I tried to implement the state machine as case..when..end Ruby statement, but that turned out to be kind of ugly, albeit it worked. Later on, I changed it to being an array of 4-element arrays (representing the initial-state, trigger-event, next-state, and optional-action). It then constituted a State Transition Table (STT), which is one implementation method for a FSM. One benefit of a STT is that the logic for enumerating the table and acting on the FSM’s logic is then separated completely from the data of the STT itself.

Another usage of FSMs, by the way, could be Graphical User Interfaces (GUIs) — I’m starting to think we just love giving everything a TLA so that we sound smarter — because if you really think about it, the GUI is always in a given state, and a user-based or internal-based event triggers it to transition into the next state. Sometimes this causes an action. For example, the initial state could be a blank window. A mouse click, key press, or asynchronous callback function may each be a trigger-event. This event would then redirect the FSM to the state of “having a minimized window”. The action taken, then, would have to correlate to the event, and thus it might be [window performMinimize] (assuming Cocoa-like/ObjC).

After I had transitioned my state machine from a when body to a STT two-dimensional table, I tried to make it look less ugly, but failed. So I created my very first DSL much like Builder, which created the STT for me. It’s used to define the body of my state transition table function. Now, it looks more readable and is probably more maintainable and flexible than the array-based version.

Also, it’s not entirely finished. As it only returns the two-dimensional array already built for you, it’s not doing a very good job encapsulating the aspect of a Finite State Machine, it just masks one part of it. So, my plan is to move all of the FSM-related logic into a Builder-like object, so that my ContentsLexer class will only be required to define the logic and data for the state machine to work, and be able to output its tokens method — this is the sole purpose of the ContentsLexer class after all, it just takes in a raw string and tokenizes it for the upcoming ContentsParser state machine which will transform the tokens into an Abstract Syntax Tree. I could be wrong about how that part will function, though, as I only started my research into it on late Friday. But the idea I have in my head for it is that it will probably be a recursive hash containing an abstract representation of the final markdown syntax.. and when I imagine it, I see Lisp’s s-expressions. But anyway I’m digressing, aren’t I?

According to Eric, FSMs can be used to represent practically everything, as it’s almost a universal principle or rule, much like the Turing Machine, such that everything else more complex can be boiled down into a finite state machine. Given this is true, we can expect that xkcd will soon post a meta-comic about the world actually being a simulation of FSMs.

About me


My name is Steven Degutis, and I've been writing software professionally for a decade. During that time, I've written many apps and websites, quite a few technical articles, and kept up-to-date with the rapidly evolving software industry.

If you have software needs for web, mobile, or desktop, and are looking for a seasoned software professional, please reach out to me at to set up a phone call.

Work Experience

  • Self-employed – present
  • Clean Coders – 5 years
  • 8th Light – 2 years
  • Big Nerd Ranch – 1 year
  • Self-employed - 1 year


  • Web: full-stack
  • iOS (UIKit)
  • macOS (Cocoa)
  • AWS / EC2 / ELB


  • JavaScript
  • HTML5 / CSS
  • Swift
  • Objective-C
  • Clojure


  • Node.js
  • Express.js
  • React
  • Vue.js
  • Electron

Technical articles

Over the past decade, I've written a total of 172 technical articles on various programming languages, frameworks, best practices, and my own projects, as I kept up-to-date and active in the software industry.

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Here are some of the projects I'm most proud of. They were created using a variety of technologies, running on several different platforms and OSes. They're all finished products, and many of them are open source.

Website - Online Video Store

I wrote this web store for Robert "Uncle Bob" Martin, using Clojure for the back-end, and JavaScript for the front-end. Over the course of 5 years, I took the site from a simple three-page website to a full enterprise-ready business solution, with nearly 100% test coverage.

  • Clojure
  • Datomic
  • jQuery / D3.js
  • JavaScript
  • ClojureScript


macOS app - Dock Utility

I made Docks in 2009 for users who wanted to swap out icons in their Dock with a single click. Its unique functionality and design aesthetic attracted the attention of Apple, Engadget, MacWorld, and led to an acquisition of my start-up by Big Nerd Ranch.

  • Staff Pick
  • MacWorld 4/5 Rating
  • MacWorld Gem of the Year
  • Featured on


macOS app - Clojure IDE

Source Code

While working on, a website written completely in Clojure, I increased my productivity by building a custom IDE for macOS designed specifically for Clojure projects.

  • Objective-C
  • Clojure
  • C / C++
  • Cocoa
  • Themeable


macOS app - Hackable Automation

Source Code

This began as an experiment to see how many languages I could use to script a custom macOS window manager using our custom TCP protocol. Eventually it had bindings for Clojure, Ruby, Python, Go, JavaScript, CoffeeScript, Node.js, Chicken Sceme, and Racket, as well as other community additions.

  • TCP / Unix sockets
  • Custom protocol
  • Highly Scriptable
  • 10+ language bindings
  • Open source community

Bubble Maker

iOS app - Bubble simulator

This toy was made in a weekend to entertain my 1 year old daughter. It lets you create bubbles with your fingers, which then simulate physics by bumping into each other and falling.

  • SpirteKit
  • Custom art
  • Physics simulation
  • iOS
  • tvOS

Quick List

iOS app - Todo list app

When I couldn't find an app in the App Store that let me make very simple lists extremely quickly, I made one myself. I use it almost every day to organize and track my activities.

  • In-app purchases
  • Custom UI / UX
  • Social media
  • App Store artwork
  • Spring animations

Website - Personal Portfolio

Source Code

This very site itself was written from scratch in about a day. It uses best practices for modern responsive web design, and a custom build phase to compile the sources into a single HTML file.

  • Node.js
  • Pug / Jade
  • LessCSS
  • HTML5
  • WebSockets


Java app - Game

Source Code

The game 2048 (created by Gabriele Cirulli) is so fun that my kids wanted their own copy. So I wrote this version in Java 8, using JavaFx for attractive graphics and silky smooth animations.

  • Java 8
  • JavaFx
  • Modular code
  • Customizable
  • Animations


macOS app - Window Manager

Source Code

I created this app to increase my productivity by letting me move windows around in macOS using keyboard shortcuts. It grew into a community-driven highly extensible app, using Lua for its plugin system.

  • Objective-C
  • Embedded Lua
  • Plugin system
  • Fully documented
  • 5,000 GitHub stars

Website - Social Network

Implementing this elite social network gave me experience integrating both Apple Pay and credit card payments (via seamlessly into web apps, for a frictionless and pain-free payment experience.

  • Clojure
  • Elastic Beanstalk
  • PostgreSQL
  • Apple Pay


Website - Live Chatroom

Source Code

This isn't just any chatroom. In this web app, you can see what everyone is typing while they type it. I made this in order to scratch my itch for making real-time apps and games, and learned how to use WebSockets in the process.

  • JavaScript
  • WebSockets
  • Node.js
  • Vue.js
  • CSS


macOS app - Music Player

Source Code

As iTunes went through many user interface changes, I wanted an app that was consistent, intuitive, and easy to use. So I created Bahamut, a minimal music player for macOS with a custom user interface.

  • Objective-C
  • Custom UI
  • Cocoa
  • Core Data
  • AVFoundation


macOS app - Chat (IRC) Client

Source Code

This was written in 2009, before the time of Slack, when IRC was the main way for programmers to get short-term assistance from each other. Its purpose was to be a beautiful app with an emphasis on simplicity and usability over technical power.

  • Async networking
  • Core Animation
  • Core Text
  • IRC Protocol
  • UI Design


macOS app - Window Manager

Source Code

This is an app I actually use every single day. It lets you move windows with global keyboard shortcuts. Since it uses Vim-like key bindings, it should feel pretty natural to any programmer. There's no configuration needed; it Just Works™.

  • Minimalist UI
  • Simple UI
  • Vim-like Hotkeys
  • Global Hotkeys
  • Zero-configuration


macOS app - Lua window manager

Source Code

As an evolution of Phoenix, Hydra was my first attempt at embedding a full Lua virtual machine into an Objective-C app, to make a lightweight and efficient window manager that focused on speed, low memory usage, low CPU usage, and overall being gentle on laptop batteries.

  • Embedded Lua
  • Generated docs
  • Lightweight
  • Memory efficient
  • CPU efficient


macOS app - JavaScript window manager

Source Code

As an evolution of Zephyros, Phoenix was my attempt to use Cocoa's native JavaScript bindings to make a more lightweight and efficient window manager, that focused on speed, low memory usage, low CPU usage, and overall being gentle on laptop batteries.

  • JavaScriptCore
  • JavaScript API
  • Lightweight
  • Memory efficient
  • CPU efficient

Smaller projects

These may be tiny, but they're interesting technical feats.

Lua4Swift Swift framework for embedding Lua with a native Swift API.
choose Command line fuzzy-matching tool for macOS that uses a GUI
music Command line music daemon for macOS that only speaks JSON
hecto Command line text editor with an embedded Lua plugin system
ZephSharp Window manager for Windows using Clojure for scripting
management Minimalist EC2 configuration & deployment tool in Ruby.
go.assert Assertion helper package for writing tests in Go.
go.shattr Go library for printing shell-attributed strings to stdout.
OCDSpec2 Objective-C based testing framework with Xcode integration.