(define-record-type :rule
  (make-rule prereqs wants-build? build-func)
  is-rule?
  (prereqs rule-prereqs)
  (wants-build? rule-wants-build?)
  (build-func rule-build-func))

(define-record-type :rule-set
  (make-rule-set rules)
  is-rule-set?
 (rules rule-set-rules))

(define (make-empty-rule-set)
  (make-rule-set '()))

;;; listen-ch is a dummy here
;;; now this and the one in make-rule.scm 
;;; are almost the same functions
(define (rule-set-add rule rule-set)
  (let ((listen-ch #f))
    (if (not (assq rule (rule-set-rules rule-set)))
	(make-rule-set (alist-cons rule listen-ch (rule-set-rules rule-set)))
	(error "make-rule: rule already exists."))))

;;;
;;; RULE-RESULT
;;; 
;;; (rule-result-wants-build? rule-result) --->  
;;;    (wants-build?-result . cooked-state) oder (#f . cooked-state) 
;;; 
;;; (rule-result-build-func rule-result) --->  
;;;    (build-func-result . end-state) oder #f 
;;; 
;;; (rule-make rule init-state rule-set) ---> rule-result
;;; 
(define-record-type :rule-result
  (make-rule-result wants-build?-result build-func-result)
  is-rule-result?
  (wants-build?-result rule-result-wants-build?)
  (build-func-result rule-result-build-func))

(define (rule-make rule init-state rule-set)
  (let* ((pre-results (map (lambda (prereq) 
			     (if (assq prereq (rule-set-rules rule-set))
				 (rule-make prereq init-state rule-set)
				 (error "prerequisite is not in rule-set!")))
			   (rule-prereqs rule)))
	 (wants-build?-result (apply (rule-wants-build? rule) 
				     (append pre-results (list init-state))))
	 (build-required? (car wants-build?-result))
	 (cooked-state (cdr wants-build?-result)))
    (if build-required?
	(make-rule-result wants-build?-result
			  (apply (rule-build-func rule)
				 (append (list build-required?)
					 pre-results 
					 (list cooked-state))))
	(make-rule-result wants-build?-result #f))))