Intro to Erlang
May 19, 2009
Ken Pratt
http://kenpratt.net/

What is Erlang?
+ =
Open
Source

History
Created in ’86
Open-sourced in ’98
“Programming Erlang” published in ’07
Taking off in popularity (3 more books on the way)

Ruby killer?
Absolutely not!

The philosophy
Simple language
Ultra-lightweight concurrency
No shared state (and no locks, no mutexes)
<3 asynchronous message passing
Processes should be able to run forever

The language
Functional
Strong, dynamic typing
NO shared state(!!) (and no mutable variables)
Pattern matching on steroids
<3 tail recursion
Compiled to bytecode, runs on VM

Silly code example

Architecture
= light-weight process with a built-in mailbox

Distributed architecture
= light-weight process with a built-in mailbox

Concurrent programming
It is VERY easy to turn procedural code into concurrent
code (as long as you follow conventions)
Code with race conditions either goes in a singleton
process or in a transaction in Mnesia
It is harder to write distributed applications, but still
much, much easier than most platforms (primarily due
to no shared state, no locks, no synchronization, etc...)

Libraries
Native and “OTP” libraries do all the concurrency heavy
lifting for you
Supervisor trees
Mnesia distributed database
Web frameworks (Nitrogen, Webmachine)
JSON!

So what?
Who the hell would use
this obscure functional crap?

Highly-concurrent phone switching servers
99.9999999% uptime (~3ms down/year)
Soft real-time characteristics
Fault tolerant

Facebook Chat backend
7+ million active chat channels at peak
~100 servers (= 700,000 channels/server)
AJAX + Comet (long-polling)

Amazon SimpleDB
Schema-less database

IM client integration
ejabberd (Erlang Jabber service)

Chat room polling in Campfire
283 LoC
1500 req/sec

...and many more

Ruby + Erlang
They can work together

Katamari/Fuzed
Rails server clustering
Erlang bindings for Rails
YAWS web server

Nanite
A “self-assembling cluster of Ruby daemons”
Daemons can be anything small or large, including a
Rails server or map/reduce tasks
RabbitMQ handles the distributed stuff

Erlectricity
“Real” Erlang/Ruby interaction
Bi-directional communication using Erlang’s binary
format
Erlang treats Ruby processes as “just another” Erlang
process

BUT
“Use the right tool for the right job.”
Erlang is great for distributed services...
...but Ruby is still king for expressing business logic.

Where to start
“Programming Erlang”
by Joe Armstrong
(creator of Erlang)
Slides & videos online!
(I’ll post the link to the mailing list)
http://www.erlang-factory.com/
conference/SFBayAreaErlangFactory2009

Erlang meetup
http://www.meetup.com/erlang-vancouver
First meetup in mid-to-late June
“Intro to Erlang Programming”(?)
Definitely won’t conflict with Ruby meetup
Thanks!