KnowledgeWorks and Prolog User Guide > B Examples


B.1 The Tutorial

The code for the tutorial (Tutorial) is reproduced for easy reference.

; -*-mode : lisp ; package : kw-user -*- (in-package kw-user) ;;; ---------------- OBJECT DEFINITIONS ------------
(def-kb-class node ()
   ((animal :initform nil :accessor node-animal
            :initarg :animal)
    (question :initform nil :accessor node-question
              :initarg :question)
    (yes-node :initform nil :accessor node-yes-node
              :initarg :yes-node)
    (no-node :initform nil :accessor node-no-node
             :initarg :no-node)))
(def-kb-class root ()
   ((node :initform nil :accessor root-node
          :initarg :node)))
(def-kb-struct current-node node)
(def-kb-struct game-over node animal answer)
;;; -------------- FORWARD CHAINING RULES -------------
;;; if there is no question we are about to ask then
;;; ask the question which is the root question of the
;;; question tree
(defrule play :forward
  (root ?r node ?node)
  (not (current-node ? node ?))
     (format nil "  ANIMAL GUESSING GAME - ~
          think of an animal to continue")))
  (assert (current-node ? node ?node)))
;;; ask a yes/no question - these are non-leaf questions
(defrule y-n-question :forward
  (current-node ?current node ?node)
  (node ?node animal nil question ?q yes-node ?y-n
    no-node ?n-n)
  ((tk:confirm-yes-or-no ?q) ?answer)
  (erase ?current)
  ((find-new-node ?answer ?y-n ?n-n) ?new-current)
  (assert (current-node ? node ?new-current)))
(defun find-new-node (answer yes-node no-node)
  (if answer yes-node no-node))
;;; ask an animal question - these a leaf questions
(defrule animal-question :forward
  (current-node ?current node ?node)
  (node ?node animal ?animal question nil)
     (format nil "Is it a ~a?" ?animal)) ?answer)
  (erase ?current)
  (assert (game-over ? node ?node animal ?animal
    answer ?answer)))
;;; add new nodes to the tree for the new animal and
;;; the question that distinguishes it
(defrule new-question :forward
  :priority 20
  (game-over ? node ?node animal ?animal answer nil)
  (fetch-new-animal ?new-animal)
    (format nil "Tell me a question for which the ~
           answer is yes for a ~a and no for a ~a"
           ?new-animal ?animal)) ?question)
  (assert (node ?yes-node question nil 
           animal ?new-animal))
  (assert (node ?no-node question nil animal ?animal))
  (assert (node ?node animal nil yes-node ?yes-node
           no-node ?no-node question ?question)))
;;; game is over
(defrule game-finished :forward
  :priority 15
  (game-over ?g)
  (erase ?g)
;  (test (not (tk:confirm-yes-or-no "Play again?")))
;;; --------------- BACKWARD CHAINING ---------------- ;;; prompt user for new animal
(defrule fetch-new-animal :backward
   ((fetch-new-animal ?new-animal)
;    (repeat)
                "What was your animal?"))
    (not (= ?new-animal "NIL")) 
                ; check if abort was pressed
     (doesnt-exist-already ?new-animal)
     (and ((tk:send-a-message "Animal exists already"))
;;; check if a node already refers to this animal
(defrule doesnt-exist-already :backward
  ((doesnt-exist-already ?animal)
   (node ? animal ?animal)
  ((doesnt-exist-already ?animal)
   <-- ))
;;; --------------- SAVING THE ANIMAL BASE ------------
;;; writes out code which when loaded reconstructs the
;;; tree of questions
(defun save-animals (filename)
  (let* ((start-node (any `?node `(root ? node ?node)))
         (code `(make-instance `root
                 :node ,(node-code start-node)))
         (*print-pretty* t))
     (stream filename :direction :output
                      :if-exists :supersede)
      (write `(in-package kw-user) :stream stream)
      (write-char #\Newline stream)
      (write code :stream stream))
(defun node-code (node)
  (when node
    `(make-instance `node 
                   :question ,(node-question node)
       :animal `,(node-animal node)
       :yes-node ,(node-code (node-yes-node node))
       :no-node ,(node-code (node-no-node node)))))

KnowledgeWorks and Prolog User Guide (Macintosh version) - 22 Dec 2009