logos

I second The Reasoned Schemer as a fantastic introduction to logic programming. You can get miniKanren and its variants here - http://code.google.com/p/iucs-relational-research/. They'll run in pretty much any R5RS Scheme. If you're a Clojurian you can give my bells & whistles implementation a spin: https://github.com/swannodette/logos. It has good performance, tabling, pattern-matching, and disequality constraints.

Follow Norvig's lead from Paradigms of Artificial Inteligence - write fast embedded paradigms. So write a performant Constraint Solver DSL couple it with a performant Prolog DSL. Solve all kinds of problems declaratively instead of just Sudoku. I've been working on that https://github.com/swannodette/logos ;)

It's called "mini-kanren", see also William Byrd's thesis. Or wait for swannodette to show up. :) He's writing a Clojure port: http://github.com/swannodette/logos

You can easily create true one-at-a-time lazy-sequences. I've been working on my own implementation of miniKanren (from The Reasoned Schemer) in Clojure. It's been quite challenging since the original implementation assumes the presence of TCO. Also one-at-time laziness is very much required here to enforce interleaving of streams results and to avoid divergence. I was happy to find I could get the same non-stack consuming behavior and that it turns out to perform better than miniKanren under Racket. https://github.com/swannodette/logos/blob/master/src/logos/m...