Thank you for reading the 馃悞 book!
The "listings" folder contains all the code samples used in the book. The naming format is the number of a chapter followed by the ordinal number of the code sample in the chapter.
One more thing... keep an eye on this repository, as I'm working on some bonus content for the 馃悞 book's readers: an open-source implementation of a subset of the Wolfdesk ticketing system described in the book's Preface.