slidenumbers: true
Erlang.
======
### Fault-tolerant, concurrent programming.
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## A brief history of Erlang
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^ Telefontornet in Stockholm, around 1890. Used until 1913.
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^ Telephones were operated manually at Switchboards. Anyone old enough to remember? I'm certainly not.
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^ Eventually we did that in software, and we got better at it over time. Ericsson AXD 301, first commercial Erlang switch. But lets take a step back.
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## Phone switches must be ...
Highly concurrent
Fault-tolerant
Distributed
(Fast!)
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## ... and so is Erlang!
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## Erlang as a whole:
- Unique process model (actors!)
- Built-in fault-tolerance & error handling
- Distributed processes
- Three parts!
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## Part 1: Erlang, the language
- Functional
- Prolog-inspired syntax
- Everything is immutable
- *Extreme* pattern-matching
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### Hello Joe
```erlang
hello_joe.
```
---
### Hello Joe
```erlang
-module(hello1).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.
```
---
### Hello Joe
```erlang
-module(hello1).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.
% 1> c(hello1).
% {ok,hello1}
% 2> hello1:hello_joe().
% hello_joe
```
---
### Hello Joe
```erlang
-module(hello2).
-export([hello/1]).
hello(Name) ->
io:format("Hello ~s!~n", [Name]).
% 3> c(hello2).
% {ok,hello2}
% 4> hello2:hello("Joe").
% Hello Joe!
% ok
```
---
## [fit] Hello ~~world~~ Joe is boring!
## [fit] Lets do it with processes.
---
### Hello Server
```erlang
-module(hello_server).
-export([start_server/0]).
start_server() ->
spawn(fun() -> server() end).
server() ->
receive
{greet, Name} ->
io:format("Hello ~s!~n", [Name]),
server()
end.
```
---
## [fit] Some issues with that ...
- What about unused messages?
- What if the server crashes?
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## [fit] Part 2: Open Telecom Platform
### **It's called Erlang/OTP for a reason.**
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# OTP: An Application Framework
- Supervision - keep processes alive!
- OTP Behaviours - common process patterns
- Extensive standard library
- Error handling, debuggers, testing, ...
- Lots more!
^ Standard library includes lots of things from simple network libraries over testing frameworks to cryptography, complete LDAP clients etc.
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# Supervision
^ Supervision keeps processes alive, different restart behaviours, everything should be supervised to avoid "process" (and therefore memory) leaks
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# OTP Behaviours
* `gen_server`
* `gen_statem`
* `gen_event`
* `supervisor`
^ gen = generic. explain server, explain statem, event = event handling with registered handlers, supervisor ...
---
`gen_server`
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## [fit] Part 3: BEAM
### Bogdan/Bjørn Erlang Abstract machine
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## A VM for Erlang
* Many were written, BEAM survived
* Concurrent garbage-collection
* Lower-level bytecode than JVM
* Very open to new languages
(Elixir, LFE, Joxa, ...)
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## What next?
* Ole's talk, obviously!
* Learn You Some Erlang!
www.learnyousomeerlang.com
* Watch out for the Oslo BEAM meetup group
