IMT Atlantique : Elixir live coding for the erlang Actor Model

Unprepared live-coding session to explain concepts during the course. For those interested in a job or intern position, please contact me through : contact@kbrw.fr or add my associate linkedIn (he is aware of the IMT class and your interest) : https://www.linkedin.com/in/jerome-benoliel-6b260316/. No need to be hesitant Jerome can explain you the company, and our big and interesting projects for large industry and retail groups.

Please :

first install elixir to really test the files : http://elixir-lang.github.io/install.html.
Then read the course slides : slides in this repo
Then clone this repo to test : git clone https://github.com/awetzel/imt_actor_course_2017
Then read this README and each part course_part_x.exs files
Then and only then (actor principles are more important than the given language) read the Elixir language documentation http://elixir-lang.github.io/getting-started
If you want to read the same in the erlang language : read http://learnyousomeerlang.com/content

The use case is to manage a bank account

with an initial credit hold of 4 €
then credit 5€
then credit 2€
then debit 3€
then show current credit hold : should be 8€

This course try to "show" the principles of the actor model, how it is applied in practice in a functional language (Erlang/Elixir). The idea is to build the "account application" incrementally :

part0: from scratch first : with only a raw functional language
part1: then with a micro-process/coroutine system sending message
part2: then splitting the generic server logic from the business account logic
part3: then with the Erlang/Elixir libraries to create the coroutine
part4: then with a supervisor to handle error and restart the coroutine
part5: then with the Erlang/Elixir libraries to create the supervisor
part6: then with the Erlang-OTP/Elixir-tooling way to create the concept of "application"

Part 0 : Functional programming

elixir course_part_0.exs

standard functionnal programming : the function transform immutable data : stateless.

Problem : is you want the system to manage the bank account state, and not let an external stateful system (database, filesystem) to manage it... You need your software to be a permanent server with account in the server RAM : see course_part_1

Part 1 : Server as a linked processes with message communication

elixir course_part_1.exs

Use spawn_link, receive and send (core low level functions of erlang) to create the account server.

Part 2 : functional split : the same with a generic server

elixir course_part_2.exs

Create 2 different modules :

one to handle a generic server.
one other to handle the way you want the server to behave

Put the second module (behaviour module) in the generic server state.

Part 3 : generic server IS in standard library

elixir course_part_3.exs

Show that a complete and featurefull generic server is in the standard Library : GenServer : to build server nodes in a supervision tree. Show that it behaves exactly the same as the custom generic server developed in part 2.

Part 4 : error management : let it crash ! but supervised

elixir course_part_4.exs

Develop a special simple type of server, which role is to start child servers, and restart them when they fail. Introduce a bug to make credit 2 fail, then show that the code is still "working" - but the account server came back to it's initial working state.

Part 5 : supervisor IS in standard library

elixir course_part_5.exs

Show that a complete and featurefull supervisor server is in the standard Library : Supervisor : to build supervisor nodes in a supervision tree. Show that it behaves pretty much the same as the custom simple supervisor developed in part 4.

Part 6 : put the supervision tree into an OTP application

cd course_part_6
mix test

Erlang OTP applications includes : a configuration system, a standard way to layout your code, a standard way to start a named "root supervisor". Elixir gives you a way to build these applications with nice tooling :

config/config.exs manamement
mix.exs to describe application
test/*_test.exs files for unit testing

mix test launches the application then unit tests where the test cases has been put.

iex -S mix launches the application then give you an elixir shell connected to this application. You can try to call GenServer.call(:account_server,:get) in this shell to communicate "in live" with the account server.

awetzel / imt_actor_course_2017