Good morning,
In Chapter 5 (pages 85…86), you load the code for Flappy Dragon into a new directory. After doing this, I copied my_library from the code developed so far in the book, into the tree as you show in P86. I then proceeded to go through the following sections up to and including developing the add_phase!() macro. Moving back to Pig on P105, this is still in the more_hands directory tree, so the updates to my_library are not included in the version of my_library.
To resolve this, I then moved the newly developed version of my_library back into the more_hands tree, and made flappy_dragon_base a sub project alongside pig. Both flappy_dragon_base and the updated code for pig then compile and run as expected.
Did you intend the reader to put the flappy_dragon_base into the more_hands tree? If so, I didn’t read it like that and it might be good to clarify on pages 85 and 86 showing the directory tree from more_hands down.