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Pragmatic Erlang: Introduction

Disclaimer

Erlanger for about 7 months at IDMOG

Background: 2 years Javascript / 3 years PHP

First presentation

Why Erlang

Reliability ! 99.9999999% uptime

Handles millions of connections on a single server

Low latency

What is Erlang

Distributed / Concurrent = Scalable

Functional + Actor Model = Concurrency Oriented

Pros VS Cons

Actor model

Fault tolerant : Let it crash

Code hot swapping

Distribution / Concurrency built-in

Same code works locally and across nodes

Communication inter nodes is buit-in

Linear scaling

Tools

Simple (No curry, functors nor monads)

Side effect intensive :)

Last call optimization

Binary handling

Production shell

Dynamic typing (opinion)

Compiler is not good enough

Slow

History

Proprietary language built in 1986 by Ericsson for telecom switches

Open sourced in 1998

Distributed became Concurrent many years later

Erlang in the industry

Amazon (database)

AOL (realtime biding)

Bet365 (realtime biding)

Infinity Ward (game servers)

Ericsson (mobile networks)

Facebook (chat)

WhatsApp (chat)

Riot Game (chat)

...

Riak

CouchDB

SimpleDB

Redis

Ejabberd

RabbitMQ

Actor Model

An opinionated way of doing distribution

Everything is an isolated VM process

No shared states

Communication via message passing

Mailboxes

Processes do synchronous work

Quick syntax: Variable

1> Name = "Conan the Barbarian"."Conan the Barbarian"

2> Name."Conan the Barbarian"

3> Name = "Conan the Cimmerian".** exception error: no match of right hand side value "Conan the Cimmerian"

4> Name = "Conan the Barbarian"."Conan the Barbarian"

Quick syntax: Variable

1> Todos = [Erlang talk, Buy some milk].[Erlang talk, Buy some milk]

2> NewTodos = [Run a marathon | Todos].[Run a marathon, Erlang talk, Buy some milk]

3> NewTodos.[Run a marathon, Erlang talk, Buy some milk]

4> Todos.[Erlang talk, Buy some milk]

Quick syntax: Atom

1> atom.atom

2> atom = atom.atom

3> atom = "atom".** exception error: no match of right hand side value "atom"

4> atom = another_atom.** exception error: no match of right hand side value another_atom

Quick syntax: Pattern matching

1> [First, Second, Third] = [1, 2, 3].[1, 2, 3]

2> First.1

3> Second.2

4> Third.3

Quick syntax: Pattern matching

Basket = [apple, banana, orange, apple].

% Trying to eat somethingNewBasket = case Basket of [] -> []; [H | T] -> eat_from_basket(H)end.

Quick syntax: Pattern matching

case fetch_logged_user() of {ok, User} -> greet_user(User); {error, _} -> greet_user(John Doe)end.

{ok, User} = fetch_logged_user(),greet_user(User).

Quick syntax: Functions

% sum/1sum(List) when is_list(List) -> sum(List, 0).

% sum/2 (usually private)sum([], Total) -> Total;

sum([H | T], Total) when is_number(H) -> sum(T, Total + H).

Quick syntax: Functions

fetch_timeseries(SensorId, daily) -> fetch_daily_timeseries(SensorId);

fetch_timeseries(SensorId, weekly) -> fetch_weekly_timeseries(SensorId);fetch_timeseries(SensorId, monthly) -> fetch_monthly_timeseries(SensorId).

Quick syntax: Module

-module(robot).-export([yell/1]).

-spec yell(string()) -> string().yell(Something) when is_string(Something) string:to_upper(Something) ++ !.

1> robot:yell(exterminate).EXTERMINATE!

Quick syntax: Processes

spawn(N, M, F, A).spawn_monitor(N, M, F, A). spawn_link(N, M, F, A).

1> self().

2> Pid = spawn(fun() -> io:format(Hello from ~p, [self()]) end).

Hello from
3> Pid.

Quick syntax: Processes

1> self() ! do_a_backflip.do_a_backflip

2> receive Message -> io:format(Consuming message : ~p, [Message])end.Consuming message : do_a_backflipdo_a_backflip

OTP

Years of good practices absorbed into the language

Behaviors

Applications

supervisor, gen_server, gen_event, gen_fsm

Directory structure

Built-in Tools

Tracer / Debugger

Processes visualizers

Unit test / Code coverage : EUnit

Static analyzer : Dialyzer

Node key value store : ETS / DETS

Distributed key value store : Mnesia

Logger: error_logger

Documentation generator: EDoc

Built-in Tools

Built-in Tools

Built-in Tools

Third party tools

REST server: Webmachine

Dependency management: Rebar

Dates: qdate

Logging: Raven

Example

Lets take a look at a quick server that keeps track of online users. Without OTP

Bonus: hot code reloading

Bonus: supervision

Bonus: multiple nodes

Variants

Elixir

Lisp Flavored Erlang

Questions?