(load "constraints.txt")

(define (squarer a b)
  (define (process-new-value)
    (if (has-value? b)
        (if (< (get-value b) 0)
            (error "square less than 0 -- SQUARER" (get-value b))
            (set-value! a (sqrt (get-value b)) me))
        (set-value! b (square (get-value a)) me)))
  (define (process-forget-value)
    (forget-value! a me)
    (forget-value! b me))
  (define (me request)
    (cond ((eq? request 'I-have-a-value)
           (process-new-value))
          ((eq? request 'I-lost-my-value)
           (process-forget-value))
          (else
           (error "Unknown request -- SQUARER" request))))
  (connect a me)
  (connect b me)
  me)

; 1 ]=> (define a (make-connector))
; 
; ;Value: a
; 
; 1 ]=> (define b (make-connector))
; 
; ;Value: b
; 
; 1 ]=> (probe 'a a)
; 
; ;Value: #[compound-procedure 12 me]
; 
; 1 ]=> (probe 'b b)
; 
; ;Value: #[compound-procedure 13 me]
; 
; 1 ]=> (squarer a b)
; 
; ;Value: #[compound-procedure 14 me]
; 
; 1 ]=> (set-value! a 2 'user)
; 
; Probe: b = 4
; Probe: a = 2
; ;Value: done
; 
; 1 ]=> (forget-value! a 'user)
; 
; Probe: b = ?
; Probe: a = ?
; ;Value: done
; 
; 1 ]=> (set-value! b 2 'user)
; 
; Probe: a = 1.4142135623730951
; Probe: b = 2
; ;Value: done