Now that the book has reached the sent to print stage I am again working through it.
Here is the repo containing the samples from the first chapter:
The first chapter works through the simplest solution to concurrency: Tasks.
It starts with a simple slow example and step by step adds more sophistication until you get to have a Task.Supervisor watching the code.
This is one of the more elegant examples of demoing the power and simplicity of Elixir tasks that I have seen.