Only the pure of heart Prolog programmer can make his way through that book!8-))
Also, Craft is organized a bit strangely -- IIRC, it was originally written as a response to a specific Prolog implementation's documentation.
I also really enjoyed _Essentials of Metaheuristics_. I bought a print copy, but thanks for putting a free PDF out there.
Prolog is also partially historic, but it has the added benefit of being logic-based, which is the direction that AI focused on for several years. Around that time, it was believed that AI could be done with pure symbolic logic, and that's exactly how programming in Prolog works. This approach eventually turned out not to work very well, but Prolog is still used in some places because it's a very easy language for interacting with graphs and decision trees (which are big things in AI).
Prolog was and still is used precisely because it is so (relatively) easy to specify some facts and behaviors as Horn clauses , which is important, because it is one of the few places I ever hear the phrase "solvable in polynomial time" in KRR.