anchor.diff:    (list (prompt-window-start-point (current-prompt-window))
           (buffer-end-point (window-buffer (current-prompt-window)))))
   
  -(defun get-prompt-string ()
  +(defun get-input-string ()
     (apply #'points-to-string (get-between-input-points)))
   
   (defun replace-prompt-input (input)
  
positive.code:       (replace-prompt-input string))))
  
  (define-command prompt-execute () ()
    (let ((input (get-prompt-string)))
      (when (or (zerop (length input))
                (null (completion-window-existing-test-function (current-prompt-window)))
                (funcall (completion-window-existing-test-function (current-prompt-window)) input))
  
negative.code: 
  (define-command prompt-previous-history () ()
    (let ((history (prompt-window-history (current-prompt-window))))
      (lem.history:backup-edit-string history (get-input-string))
      (replace-if-history-exists #'lem.history:prev-history)))
  
  (define-command prompt-next-history () ()
    (let ((history (prompt-window-history (current-prompt-window))))
      (lem.history:backup-edit-string history (get-input-string))
      (or (replace-if-history-exists #'lem.history:next-history)
          (replace-if-history-exists #'lem.history:restore-edit-string))))
  
  