;; circuit2.clp: Jess code to represent a logic circuit
;;
;; Note: this is demonstration code only;
;; IT DOESN'T WORK!
;; 
;; Modified from circuit1.clp; the idea was to separate the value
;; propagation from the structure so as to avoid the infinite loop
;; problem of circuit1.clp.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Circuit structure
;;
;; Each circuit element has a name and connectivity
;; information and a current value.

;; a NOT gate
(deftemplate not-gate "Logical not"
  (slot name)
  (slot input)
  (slot output))

;; Input port
(deftemplate input-port "Circuit input"
  (slot name)
  (slot output))

;; Output port
(deftemplate output-port "Circuit output"
  (slot name)
  (slot input))

;; Connector
;; Note that this really is unnecessary; we could just connect each
;; element directly
(deftemplate connector "Connects one input to one or more outputs"
  (slot name)
  (slot input)
  (multislot output))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Circuit activity

;; All elements have one value
(deftemplate element-state "Activity of an element"
  (slot name)
  (slot value (default unknown)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; A simple circuit

(deffacts simple "A simple circuit"
  (input-port (name in1) (output conn1))
  (connector (name conn1) (input in1) (output not1))
  (not-gate (name not1) (input conn1) (output conn2))
  (connector (name conn2) (input not1) (output out1))
  (output-port (name out1) (input conn2))
  (element-state (name in1) (value TRUE))
  (element-state (name conn1))
  (element-state (name not1))
  (element-state (name conn2))
  (element-state (name out2))
)



;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Gate rules

;; This propagates an input value from an input port to a
;; connector. IT STILL DOESN'T WORK! Why? Well, it still modifies a
;; fact on its RHS that is matched by a CE on its LHS. The modified
;; fact is still matched by that CE, and nothing else is done to
;; prevent the other CEs on the LHS from being matched, so we get the
;; rule re-activated and have an infinite loop

(defrule propagate-input "Copy value from input port to connector"
  (input-port (name ?n) (output ?c))
  (element-state (name ?n)  (value ?v&~unknown))
  ?cf <- (element-state (name ?c))
 =>
  (modify ?cf (value ?v)))