With 1.4 looming, and so little content currently available, I’m sorry, but I don’t think this makes a worthwhile buy, discount included.
Maybe 1.4 will be such a change that this book will still be relevant.
Maybe the book’s author(s) will scramble to update.
But as it stands, too little content, that was obsolete on conception (c’mon, in Dec. 2017 the 1.4 roadmap was well known, not to say anticipated)… sorry, no sell.
(And let me tell you, I’ve bought just about every book on Elixir you can think of, including obscure, self-publishing, ones. It takes a lot for me to say “pass” on an Elixir resource…)
