Peter Norvig also has two implementations of Prolog in Paradigms of AI Programming (first one is interpreted, second is complied) in Common Lisp. The book is highly recommended because Norvig's code is very elegant and his exposition is wonderful.
Allegro Prolog [1] is based on Norvig's implementation, although I'm sure they've done a fair bit of optimizing.
Allegro Prolog [1] is based on Norvig's implementation, although I'm sure they've done a fair bit of optimizing.
[1]: http://www.franz.com/products/prolog/