First off, you generally want code to read as much like logically valid relations as possible. A major strength of Prolog is that "clean" Prolog code is extreme

First off, you generally want code to read as much like logically valid relations as possible. A major strength of Prolog is that "clean" Prolog code is extremely easy to reason about with only local context. Chcek out _Clause and Effect_ by Clocksin and _The Art of Prolog_ by Sterling and Shapiro. CAE is sort of like _The Little Schemer_ for Prolog, but has a couple larger case studies as well. TAoP is one of my absolute favorite programming books - it's got as much substance as SICP. The newer edition (1994) is more expensive (though $35 used on Amazon ATM, which is a steal; it's usually more like $85-100), but adds quite a bit of new material. _The Craft of Prolog_ by O'Keefe is also good, though disorganized. (I think it was written as commentary on something else, and without that, its structure seems a bit arbitrary.) I mostly use Prolog for prototyping and exploratory programming. It would probably be more generally useful as an embedded language library, like Lua (another favorite of mine). It's a bit awkward as a fully standalone language, since things like IO don't always mix with backtracking. It's great as a rule engine, though, and would probably also be brilliant as a query language for a document-oriented database.