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;;;  generation.lisp
;;;  Written by:  Shaul Markovitch
;;;  Last time modified: 10/1/2000
;;;
;;;
;;;  This file contains procedures for generating training (and
;;;  tetsing) problems. 

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;;; The basic technique for generating problems.  It assumes that 
;;; the domain includes a function for generating random goal states.
;;; It aslo assumes that the 
;;; domain definition includes a definition of reverse operators.  It
;;; applies a random sequence of such operators on the random goal
;;; and gets an initial state.  This method guarentees that the problem
;;; is solveable.  The technique includes one parameter - the maximal
;;; length of the random sequence.
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(defparameter *random-problem-sequence-length* 10000)
(defclass problem-generation ()())

(defclass random-generation (problem-generation)
  ((sequence-length :initform  *random-problem-sequence-length*
		    :initarg :sequence-length
		    :accessor random-generation-sequence-length)))


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;;; generate-problem
;;;
;;; 
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(defmethod generate-problem
  ((domain domain)(method random-generation))
  (let* ((goal (funcall (domain-gen-goal-fn domain) domain))
	 (state (funcall (domain-state-copy-fn domain) goal))
	 (n (random-generation-sequence-length method))
	 (rev-ops (domain-reverse-operators domain)))
			    
	(loop repeat n
	      do (loop for op in (shuffle rev-ops)
		       for new-state = (funcall (domain-apply-rev-op-fn domain)
						op state domain t)

		       until new-state
		       finally (setf state new-state)))
	(make-problem :init-state state :goal-state goal)))