The KnowledgeWorks backward chaining system is an extended Prolog written entirely in Lisp and based loosely on the Warren Abstract Machine (WAM). (see An Abstract Prolog Instruction Set by David H.D. Warren, Technical Note 309 SRI International October 1983). High performance is achieved by compiling each Prolog clause into a Lisp function and handling the Prolog control flow with continuation passing. This approach removes the need for interpretation and provides easy integration with CLOS.
KnowledgeWorks and Prolog User Guide (Unix version) - 6 Dec 2011