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

const socket = connect(
`ws://${location.host}/app`,
{

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

added(line) {
addLine(line)
},

removed(i) {
app.lines.children[i].remove()
},

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
lines.push(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)
})

setInterval(
this.prune.bind(this),
this.pruneInterval * 1000
)

this.wss.on(
'connection',
this.connection.bind(this)
)
}

Steven Degutis

Full-stack software developer for hire

Allocating an AST on the stack

January 1, 2014 — 3 years ago

This week, I've been wondering if it's possible to create an Abstract Syntax Tree entirely on the C stack, without using a single call to malloc-and-friends.

Yesterday I figured out a solution. Check out the source in compiler.c [1]. It's only a lexer and parser (funny enough there's no compiler there yet), and it's about 200 lines of code.

First, I designed the tree using the traditional Lisp metaphor of "Atoms" and "Lists". For example, (+ 1 (+ 2 3)) is a list containing 2 atoms and another list, which contains 3 more atoms. [2]

Both Atoms and Lists live inside an Element struct type, specifically inside a C-union. This shrinks the space it takes up, while ensuring that an Atom and a List-node take up an identical amount of space.

Atoms contain self-sufficient data. List-nodes have a pointer to the Element they represent at that spot in the list, and a pointer to the next List-node in the list. An empty list is represented by a single List-node with both pointers set to NULL. This also serves as the tail of any list.

Since all Elements take up the same amount of space, I was able to declare a C-array of Elements on the stack. I used the size of the input-string as the number of Elements to hold, figuring that all Atoms and List-nodes combined can't be more than the number of characters in the source code.

Then it was just a matter of passing this array into the recursive-descent parser. Every time I needed to "allocate" a new Element in the parser, I would just grab the next Element off the C-array and use its address as a pointer. This required keeping track of what offset (or index) the next element would be found.

That's it.

I haven't done any benchmarks, but I'm guessing this thing is probably fast-as-crazy. It's not as light on memory as it could be, since it uses a union, but I'm aiming to save cycles over memory.

Unfortunately, linked-lists are less efficient than C-arrays to navigate, and the code to do so is uglier too. So that's one trade-off that I'm not sure how I feel about yet.

The main benefit for me is that there's no need to free any memory. I can consider it officially garbage-collected and not worry at all about leaks. This is a big deal for me, since it frees up my brain to focus more on the algorithms.


  1. That's the version of the file as of the time of this writing; the latest version is here. ↩︎

  2. Or if you prefer it in Ruby: List.new(Atom.new("+"), Atom.new("1"), List.new(Atom.new("+"), Atom.new("2"), Atom.new("3"))) ↩︎

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 sbdegutis@gmail.com 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

Platforms

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

Languages

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

Frameworks

  • 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.

Subscribe via RSS / Atom.

Chronological

Portfolio

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.

CleanCoders.com

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

Docks

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.

  • Apple.com Staff Pick
  • MacWorld 4/5 Rating
  • MacWorld Gem of the Year
  • Featured on Engadget.com

Leviathan

macOS app - Clojure IDE

Source Code

While working on CleanCoders.com, 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

Zephyros

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

sdegutis.com

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

2048

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

Mjolnir

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

AffluentConfidante.com

Website - Social Network

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

  • Clojure
  • Elastic Beanstalk
  • PostgreSQL
  • Stripe.com
  • Apple Pay

HyperChat

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

Bahamut

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

Chatter

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

AppGrid

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

Hydra

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

Phoenix

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.