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

Ambiguities in Programming Language Grammars

July 24, 2016 — 2 years ago

Okay, let's get straight to it, because fluffy writing just isn't compatible with my semi-autistic brain. This blog post explains what programming language ambiguities are, how they happen, and how to avoid them when designing a programming language grammar. There's literally no point in me writing it, because you'll only want to read on ahead if you're into amateur programming language design, but only mildly, and thus spend no time trying to figure this out yourself, since otherwise you'd have already known everything written here.

We'll use good old trusty EBNF for our simple language.

If you've forgotten or don't know EBNF, it's mostly self-explanatory. The ::= makes a definition. The | means it can be either the thing on the left or the thing on the right. Literal strings are enclosed in single-quotes. The {...} syntax allows 0 or more of these things. The [...] syntax allows 0 or 1 of these things. And sometimes (...) is needed to groups things, to disambiguate the | thing.

So, given the following grammar:

expr ::= Number | Symbol | array | assignment ;

assignment ::= Symbol '=' expr ;

array ::= '[' [expr {',' expr}] ']' ;

We could then write:

a = 0
b = [1, 2, 3]
c = []

Dead simple stuff here. You have variables ("symbols"), numbers, assignments, and arrays.

To keep things super simple, let's just say a Symbol can only be a through z, and a number can only be 0 through 9, and both can only be one character long.

Now, what if you wanted hashmaps? Let's use the syntax [a=1,b=2]:

expr ::= Number | Symbol | array | assignment | hashmap;

assignment ::= Symbol '=' expr ;

array ::= '[' [expr {',' expr}] ']' ;

hashmap ::= '[' [assignment {',' assignment}] ']' ;

So now we can write:

a = 0
b = [1, 2, 3]
c = [d = 4, e = 5]

But wait? What's that last line? Is it a hashmap? Or an array of assignments? Also, is [] an empty array, or an empty hashmap?

Oh, the Ambiguity!!!

Okay, so let's fix that by changing it to use { these } delimters, instead of sharing with array, and let's add a colon to separate keys from values. Nothing else is using those so far, so it should be fine:

expr ::= Number | Symbol | array | assignment | hashmap;

assignment ::= Symbol '=' expr ;

array ::= '[' [expr {',' expr}] ']' ;

keyvalue ::= expr '=' expr ;

hashmap ::= '{' [keyvalue {',' keyvalue}] '}' ;

So now we can write:

a = 0
b = [1, 2, 3]
c = {d : 4, e : 5}

Great! Now that last line isn't ambiguous! Plus, now we know that [] is an empty array, and {} is an empty hashmap!

Okay, but what if we want to start using { these } delimiters for blocks of expressions grouped together?

expr ::= Number | Symbol | array | assignment | hashmap | block;

assignment ::= Symbol '=' expr ;

block ::= '{' [expr {';' expr}] '}'

array ::= '[' [expr {',' expr}] ']' ;

keyvalue ::= expr '=' expr ;

hashmap ::= '{' [keyvalue {',' keyvalue}] '}' ;

So now we can write:

a = { 0 ; [1, 2, 3] }
b = {x : 4, y : 5}
c = {}

Oh crap. What is c? Is it the result of an empty block of code? (The grammar does allow that, mind you.) Or, is it an empty hashmap? Crap crap crappity crap.

Two simple resolutions come to mind:

  1. Change the syntax for empty hashmaps. This is ugly because it creates an inconsistency. One simple example is {:} is an empty hashmap whereas {} is an empty block. Doable, but ugly.

  2. Disallow empty code blocks. But empty code blocks are sometimes useful. Like, when you want to give a no-op callback function.

Solution #1 would change the grammar like so:

-hashmap ::= '{' [keyvalue {',' keyvalue}] '}' ;
+hashmap ::= '{' (':' | keyvalue {',' keyvalue}) '}' ;

Solution #2 would change it like this:

-block ::= '{' [expr {';' expr}] '}'
+block ::= '{' expr {';' expr} '}'

Okay that's it. Bye.

About me

My name is Steven Degutis, and I've been writing software professionally for almost a decade. During that time, I've written many apps and websites, quite a few techical 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 169 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.

Lua4SwiftSwift framework for embedding Lua with a native Swift API.
chooseCommand line fuzzy-matching tool for macOS that uses a GUI
musicCommand line music daemon for macOS that only speaks JSON
hectoCommand line text editor with an embedded Lua plugin system
ZephSharpWindow manager for Windows using Clojure for scripting
managementMinimalist EC2 configuration & deployment tool in Ruby.
go.assertAssertion helper package for writing tests in Go.
go.shattrGo library for printing shell-attributed strings to stdout.
OCDSpec2Objective-C based testing framework with Xcode integration.