The document provides an overview of a hands-on session on Erlang and Elixir, highlighting the similarities and differences between the two programming languages, particularly in syntax, design, and use cases. It covers fundamental concepts such as lightweight processes, message passing, and supervision in Erlang, as well as practical examples of creating modules and processes. The session aims to introduce attendees to Erlang's features and the OTP framework while promoting Elixir's ease of use and better meta-programming support.

1. Erlang
Elixir Webilea Hands-On Session
at Obst & Gemüse, 19.3.2014
By André Graf
@der_graf / @erlio_basel

2. Preliminaries
● Erlang and Elixir Programs are compiled for
the BEAM*
● Similar datatypes and runtime behavior
● Different syntax, language features, stdlib
*Bogdan/Björn's Erlang Abstract Machine

3. 1986
Erlang has been developed
by Ericsson, for building
highly available telco
systems
Massively concurrent
server systems
Server systems
that run forever
Hot-Code
Upgrades
Inherently parallel
problem domain
High availability
through redundancy
Debugging
Live Systems

4. ● Functional
● Compiled
● Dynamically typed
● VM & Shell
● Very lightweight processes
● Processes don't share state
● Message Passing Concurrency
● Process Supervision (Let it crash)
● Built-in Distribution
● Hot-Code Upgrades

5. Erlang OTP
● Architecture Patterns
● Middlewares
● Libraries
● Tools
● You could use Erlang witout OTP (nobody does)
● OTP is included in the Erlang distribution
● OTP is closely tied to the Erlang VM

6. 1998
Erlang has been
opensourced and other
companies started using it.
Ericsson went for C++
Massively concurrent
server systems
Server systems
that run forever
Hot-Code
Upgrades
Inherently parallel
problem domain
High availability
through redundancy
Debugging
Live Systems

7. 2007

9. 2012

10. ● Functional
● Compiled
● Dynamically typed
● VM & Shell
● Very lightweight processes
● Processes don't share state
● Message Passing Concurrency
● Process Supervision (Let it crash)
● Built-in Distribution
● Hot-Code Upgrades

11. Erlang vs. Elixir
very subjective
+ Elixir has a more familiar Syntax.
+ Elixir fixes several language design mistakes
from the past. *
+ Elixir will bring more people to the Beam.
+ Elixir has better meta-programming support.
- Elixir has (currently) no own OTP framework.
> killer for production use.
* http://joearms.github.io/2013/05/31/a-week-with-elixir.html

12. Erlang Hands-On
1. Installation Party
2. Language introduction http://www.tryerlang.org/
3. My first Erlang module
4. My first Erlang process
5. Let it crash
6. OTP behaviours gen_server / supervisor
7. Recap / Discussion

13. Language Introduction
Goto http://www.tryerlang.org/

14. My first Erlang Module
● Module-Name == Filename.erl
– e.g. my_first_module.erl
-module(my_first_module).
-export([my_first_function/1]).
% this is a comment for my first function
% this is another line of the comment
my_first_function(Param) ->
io:format(“wow my first function got called with param: ~p~n”, [Param]).
1. Compile with erlc my_first_module.erl
2. Start Erlang shell with: erl
3. Call function my_first_module:my_first_function(“hello world”).

15. My first Erlang Process
-module(my_first_module).
-export([my_first_function/0,
start_my_first_process/0]).
my_first_function() ->
receive
Msg ->
io:format(“wow my first process got a msg: ~p~n”, [Msg])
end.
start_my_first_process() ->
spawn(?MODULE, my_first_function, []).
1. Compile with erlc my_first_module.erl
or if you are inside the shell with:
c(my_first_module).
l(my_first_module).
2. Start your first process:
Pid = my_first_module:start_my_first_process().
3. Send your first message:
Pid ! yeah_this_is_my_first_message.
4. How can you reuse the Process???

16. Let it Crash
-module(my_first_module).
-export([my_first_function/0,
start_my_first_process/0]).
my_first_function() ->
receive
Msg ->
dispatch_my_msg(Msg),
my_first_function() %% yay, recursion!
end.
start_my_first_process() ->
spawn(?MODULE, my_first_function, []).
dispatch_my_msg({hello, world}) ->
io:format(“what a great hello world~n”);
dispatch_my_msg({A, B}) ->
io:format(“tuple with ~p and ~p~n”, [A,B]).
1. kinda stupid dispatcher, right???

17. Let it Crash
-module(my_first_module).
-export([my_first_function/0,
start_my_first_monitored_process/1,
my_monitor/1]).
my_first_function() ->
receive
Msg ->
dispatch_my_msg(Msg),
my_first_function()
end.
my_monitor(ProcName) when is_atom(ProcName) ->
Pid = spawn(?MODULE, my_first_function, []),
true = register(ProcName, Pid),
MonitorRef = monitor(process, Pid),
receive
{'DOWN', MonitorRef, _Type, Pid, _Info} ->
my_monitor(ProcName);
stop ->
demonitor(MonitorRef)
end.
start_my_first_monitored_process(ProcName) ->
spawn(?MODULE, my_monitor, [ProcName]).
...

18. OTP Behaviours
● gen_server
– Generic way to write servers in Erlang OTP Style
● Supervisor
– A Supervisor that supervises other OTP compliant
processes (e.g. gen_servers, gen_fsms)

19. gen_server
-module(sample_gen_server).
-behaviour(gen_server).
-export([start_link/0]).
%% gen_server callbacks
-export([init/1,
handle_call/3,
handle_cast/2,
handle_info/2,
terminate/2,
code_change/3]).
%%% API
start_link() ->
gen_server:start_link(?MODULE, [], []).
%%% gen_server callbacks
init([]) ->
{ok, []}.
handle_call(_Request, _From, State) ->
Reply = ok,
{reply, Reply, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.

20. supervisor -module(sample_supervisor).
-behaviour(supervisor).
-export([start_link/0]).
%% Supervisor callbacks
-export([init/1]).
%% ===================================================================
%% API functions
%% ===================================================================
start_link() ->
supervisor:start_link({local, ?MODULE}, ?MODULE, []).
%% ===================================================================
%% Supervisor callbacks
%% ===================================================================
init([]) ->
{ok, { {one_for_one, 5, 10}, [ %% 5 restarts within 10 seconds are allowed
{sample_gen_server, {
sample_gen_server, start_link, []
}, permanent, 5000, worker, [sample_gen_server]}
]}}.

21. Recap/Discussion

22. Erlang
Elixir Webilea Hands-On Session
at Obst & Gemüse, 19.3.2014
By André Graf
@der_graf / @erlio_basel