Tutorial and samples combining Common Test, Gen Server, Supervisors.

© 2011 Eonblast Corporation http://www.eonblast.com. MIT Open Source License.

This is a beginner's introduction to Erlang/OTP concepts. It is structured in folders, with a README.MD in each folder that explains basics and has instructions of what to look at and what to try with the sample code.

The sample code is supposed to serve as starting point and templates for your own needs. It is usually commented in a way to help you expand on it.

Start here: https://github.com/Eonblast/erlang-arcana/tree/master/a_hellotest or read more about what this is, below.

This is what awaits:

a_hellotest				minimal Common Test suite, no test subject
b_hellotest2			complete Common Test skeleton, no test subject
c_hellotest3			minimal Common Test suite, with no functionality
d_servertest			Common Test of a minimal client and server 
e_genserver				Gen Server skeleton, no Common Test
f_genservertest			same as e but wrapped by a Common Test
g_supervisor			Supervisor skeleton, no Common Test
h_supervisortest		combines f and g for a gen server and a supervisor test suite
i_supervisortest2		same as h but with a dynamic child. look for **

These folders contain samples, building on each other, in alphabetical order. They demonstrate the Erlang OTP concepts of:

• Common Tests
• Gen Servers
• Supervisors

Common Tests are the usual way to create program tests in Erlang. Common Tests are better suited to test entire systems than Java-style Unit Tests. Generally, a Common Test simply checks if a process crashes, or not. The means to crash it, or not, are simple pattern matches by '='.

Gen Servers are the OTP way of programming servers, using the OTP behaviour 'supervisor' and herding the functional parts into a call back module that is essentially programmed in sequential tasks that are guaranteed to be run sequentially within one gen server.

Supervisors are the central OTP building blocks of program robustness and the Erlang way of programming defensively: they complement 'let it crash' with a very structured, hierarchical way to react to those crashes. Supervisors do not do anything, so they do not ever crash, except if they can't restart their worker childs at all.

The purpose of this repository is to start out or refresh your knowledge on the trivial but essential Erlang stuff beyond the language itself. It is not for learning the Erlang language, but how to use it right.

As such it is more about the OTP part in Erlang/OTP. But it really must be seen as part of Erlang proper: the Erlang way of doing things like tests, servers, and in general system development and architecture.

The Erlang language is rather small and fast to pick up despite the fact that it is 'so different' from the syntax of the Algol heirs: C, Java et al. And can I recommend Learn You Some Erlang again for the best online resource?

It gets tricky once you get past that first learning phase, into the 'standard library' area, in the case of Erlang, OTP, the 'Open Telecom Protocol', that really is not at all restricted to telecom. But its name gives a pointer to one problem: it's full of outdated backward compatibilities and low consistency in naming, parameters etc. That's great for the hard core Erlang community. Things don't change and stay the same. But it's not so great when learning Erlang for real. You need to break into the Arcana, the ancient secret arts there. And you need to learn a lot of trivial stuff that just happens to be as it is. In my experience, it's no fun at all.

It's worth it as the magic really is powerful. It's also completely inevitable to really get going with Erlang, to even really understand its power. And what you can do with it, and how you should go about it.

This repository tries to give a head start into these things. Basically, to get your head around them and get a better idea what it is all about. And, quite honestly, to enable you to then read the Erlang docs, which are made with a lot of love but also in circular dependency on knowledge you might not yet have when starting out.

So as much as possible I am trying to bring some fun back to these harder parts. I'll be happy to hear your feedback on it. Please send your pull requests with corrections, improvements, expansions. I'll be happy to include them.

hd/11

Copyright (c) 2011 Eonblast Corporation http://www.eonblast.com.

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