chickadee » sicp » probe

Probes a connector and informs upon value-change.

name

Name of the connector

connector

The connector to probe

(define (probe name connector)
  (define (print-probe value) (format #t "Probe: ~a = ~a~%" name value))
  (define (process-new-value) (print-probe (get-value connector)))
  (define (process-forget-value) (print-probe "?"))
  (define (me request)
    (case request
      ((I-have-a-value) (process-new-value))
      ((I-lost-my-value) (process-forget-value))
      (else (error "Unknown request: PROBE" request))))
  (connect connector me)
  me)