Let Erlang Crash
A fun, irreverent guide to the world’s most indestructible programming language.
“The problem with object-oriented languages is they’ve got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle.” — Joe Armstrong, creator of Erlang
What Is This?
This is a free, open-source book about Erlang — the programming language that was built to never go down, and somehow also ended up being fun.
Erlang was born in 1986 inside Ericsson, designed to run telephone switches that couldn’t afford to crash. It’s the language behind WhatsApp (handling 2 million connections per server), RabbitMQ, CouchDB, and half the world’s telecom infrastructure. It runs on the BEAM virtual machine, which is basically what would happen if someone built a VM specifically to make reliability nerds weep with joy.
This book will teach you Erlang the way it deserves to be taught: with enthusiasm, bad jokes, and a deep appreciation for the beautiful weirdness of a language where crashing is a feature.
Who Is This For?
- Programmers who are curious about Erlang but have been scared off by the syntax
- People who’ve heard “let it crash” and want to know what the hell that actually means
- Developers drowning in microservices who want to see how the grown-ups do concurrency
- Anyone who enjoys a programming book that doesn’t read like a tax form
Table of Contents
| # | Chapter | Description |
|---|---|---|
| 01 | Why Erlang? Why Now? Why Ever? | The pitch. Why a language from 1986 is more relevant than your last framework. |
| 02 | Installing Erlang (The Easy Part) | Getting the BEAM on your machine without losing your mind. |
| 03 | The Shell: Erlang’s REPL of Wonders | Your new favorite place to break things. |
| 04 | Variables Don’t Vary (And That’s Fine) | Single assignment, pattern matching, and why mutability was a mistake. |
| 05 | Atoms, Tuples, and Lists — Oh My | Erlang’s data types are weird and wonderful. |
| 06 | Pattern Matching: The Superpower | The single best feature in Erlang (fight me). |
| 07 | Functions and Modules: Where Code Lives | Writing actual programs instead of shell one-liners. |
| 08 | Recursion: Who Needs Loops? | Erlang doesn’t have for loops. You’ll be fine. |
| 09 | The BEAM: Erlang’s Secret Weapon | The virtual machine that makes everything possible. |
| 10 | Processes: Lighter Than Your Threads | Spawning a million things and not even sweating. |
| 11 | Message Passing: No Shared Memory, No Problems | How processes talk without stepping on each other. |
| 12 | Let It Crash: The Philosophy | The most misunderstood idea in programming, explained. |
| 13 | Links and Monitors: Watching Things Die | Because if something crashes, someone should know about it. |
| 14 | Error Handling: It’s Not What You Think | try/catch exists, but you probably shouldn’t use it. |
| 15 | OTP: The Batteries That Are Actually Included | The framework that makes Erlang Erlang. |
| 16 | GenServer: Your New Best Friend | The most important behaviour you’ll ever learn. |
| 17 | Supervisors: Let Someone Else Worry | Building systems that heal themselves. |
| 18 | Supervision Trees: It’s Supervisors All the Way Down | Architecting for failure at every level. |
| 19 | ETS: Stupid Fast In-Memory Storage | When you need a table and you need it now. |
| 20 | Mnesia: The Database That Lives in Your VM | A distributed database that’s also kind of bonkers. |
| 21 | Hot Code Reloading: Changing the Engine Mid-Flight | Upgrading production code without stopping. Yes, really. |
| 22 | Distributed Erlang: Nodes Talking to Nodes | Connecting BEAM instances across machines like it’s nothing. |
| 23 | Ports and NIFs: Talking to the Outside World | When you need C, Rust, or other languages to help out. |
| 24 | Testing Erlang: Yes, We Test Things | EUnit, Common Test, and property-based testing with PropEr. |
| 25 | Real-World Erlang: WhatsApp, RabbitMQ, and Friends | The systems that prove this stuff actually works. |
| 26 | Elixir: The Cool Younger Sibling | Same BEAM, different vibe. |
| 27 | Erlang Never Died | Why this weird old language keeps winning. |
License
This book is released under CC0 1.0 Universal — public domain. Do whatever you want with it. Translate it, remix it, print it and use it as a doorstop. We don’t care. Just learn some Erlang.
Contributing
Found a bug? Got a better joke? Know an Erlang fact too weird not to include? Open a PR. This book belongs to everyone.
A Note for Contributors: Erlang vs. Jekyll
This book is published via GitHub Pages using Jekyll. Jekyll’s Liquid template engine uses {{ }} for variable interpolation — which collides with Erlang’s match specifications, where {{'$1', '$2'}} is valid Erlang but looks like a Liquid tag.
If you’re writing Erlang code that contains double curly braces (common in ets:select, ets:match, mnesia:select, and match specs generally), wrap the code block in Liquid {% raw %} / {% endraw %} tags:
ets:select(people, [
{{'$1', '$2', '$3'}, [{'>', '$3', 30}], ['$2']}
]).
See the Jekyll docs on raw for details. Erlang’s syntax crashes Jekyll. Fitting, really.
Built with love, processes, and an unreasonable number of exclamation marks.