;;;; -*- Mode: Lisp; Syntax: Common-Lisp -*-
;;;; Code from Paradigms of AI Programming
;;;; Copyright (c) 1991 Peter Norvig

(<- (likes Robin cats))
(<- (likes Sandy ?x) (likes ?x cats))
(<- (likes Kim ?x) (likes ?x Lee) (likes ?x Kim))

(prolog-compile 'likes)
;;;; (DEFUN LIKES/2 (?ARG1 ?ARG2 CONT)
;;;;  (IF (UNIFY! ?ARG1 'ROBIN)
;;;;      (IF (UNIFY! ?ARG2 'CATS)
;;;;          (FUNCALL CONT)))
;;;;  (IF (UNIFY! ?ARG1 'SANDY)
;;;;      (IF (UNIFY! ?ARG2 ?X)
;;;;          (LIKES/2 ?X 'CATS CONT)))
;;;;  (IF (UNIFY! ?ARG1 'KIM)
;;;;      (IF (UNIFY! ?ARG2 ?X)
;;;;          (LIKES/2 ?X 'LEE (LAMBDA ()
;;;;                             (LIKES/2 ?X 'KIM CONT)))))) 

(<- (member ?item (?item . ?rest)))
(<- (member ?item (?x . ?rest)) (member ?item ?rest))

(prolog-compile 'member)
;;;; (DEFUN MEMBER/2 (?ARG1 ?ARG2 CONT)
;;;;  (IF (UNIFY! ?ARG1 ?ITEM)
;;;;      (IF (UNIFY! ?ARG2 (CONS ?ITEM ?REST))
;;;;          (FUNCALL CONT)))
;;;;  (IF (UNIFY! ?ARG1 ?ITEM)
;;;;      (IF (UNIFY! ?ARG2 (CONS ?X ?REST))
;;;;          (MEMBER/2 ?ITEM ?REST CONT))))