anchor.diff:    (unless (%listener-history)
       (setf (%listener-history)
             (make-history))))
  +
  +(defun listener-start-point ()
  +  (marker-point (%listener-marker)))
   
   (defun listener-start (buffer-name mode)
     (let ((buffer (get-buffer-create buffer-name)))
  
positive.code: 
  (define-key *listener-mode-keymap* (kbd "C-c C-u") 'listener-clear-input)
  (define-command listener-clear-input () ()
    (delete-region (marker-point (%listener-marker))
                   (point-max)))
  
negative.code: (defpackage :lem.listener-mode
    (:use :cl :lem :lem.util)
    (:export :listener-mode
             :*listener-mode-keymap*
             :listener-start-point
             :listener-start
             :listener-reset-prompt
             :listener-return
  