I have continued working through this beta book and have updated the github repo: github.com/chriseyre2000/designing_elixir with the samples.
So far this book is easier to follow than say Programming Phoenix since it does not keep changing the code that you are working on. The testing code is normally close to where you have typed it, so finding mistakes does not require too much effort. I would recommend using mix test after each code sample has been typed in as fixing errors can be tricky.
Note the only difference between my code and the supplied sample is the use of the british name Maths rather than Math for the sample code. My degree is in Mathematics so I can’t let a typo like that stand!
The main points from the second half of the book are the very clean validation techniques used. I like that they called the process returned by start_link a session.
The book currently stops at the end of chapter 6, so I will have to resume work on this series once it has been updated.