An easy implementation of PiL (Prolog in Lisp)

Much attention has been drawn to Prolog, the implementation of logic as a programming language. The decision of the Japanese to use Prolog as the core language of the Fifth Generation Computer [Warren, 1982] has given rise to some concern that Prolog may emerge as the chief rival to Lisp in artificial intelligence programming. I [Wallace, 1983] and others [Robinson and Sibert, 1982; Komorowski, 1982] have argued the benefits of extending Lisp to do what Prolog does. Here I present a simple procedure for implementing Prolog in Lisp (PiL), in order to demonstrate that it is easy to extend Lisp to do what Prolog does.