Ha,you beat me to it! That book was my first thought when I saw this post. I have a copy sitting here on my bookshelf.

Just to expand on how bonkers this book is... they assume that everyone has easy access to a Forth implementation. So they teach you how to build a Lisp on top of it. Then they use the Lisp you just built to build a Prolog. Then, finally, they do what the topic of the book actually is: build a simple expert system on top of that Prolog.

I love it!

To be fair, in the 1980s thanks to the Forth Interest Group (FIG), free implementations of Forth existed for most platforms at a time when most programming languages were commercial products selling for $100 or more (in 1980s dollars). It's still pretty weird, but more understandable with that in mind.