(module break mzscheme

  (require mzlib/contract)

  (provide current-breakpoint-handler)

  (define (default-current-breakpoint-handler)
    (error 'default-current-breakpoint-handler
           "The current-breakpoint-handler parameter has not yet been set in this thread."))

  (define current-breakpoint-handler
    (make-parameter
     default-current-breakpoint-handler
     (lambda (new-handler)
       (if (and (procedure? new-handler)
                (procedure-arity-includes? new-handler 0))
         new-handler
         (error 'current-breakpoint-handler
                "Bad value for current-breakpoint-handler: ~e"
                new-handler)))))

  (provide/contract [break (-> any)])

  (define (break)
    ((current-breakpoint-handler))))