anchor.diff:  (define-command !prompt () ()
     (message "~A"
              (!prompt-for-line "hello: "
  -                             "cxxxr"
  -                             lem::*minibuffer-buffer-complete-function*
  +                             ""
  +                             nil
  +                             nil
  +                             #+(or)
                                (lambda (name)
                                  (member name (buffer-list) :test #'string= :key #'buffer-name))
                                nil)))
  
positive.code: (defun delete-prompt (prompt-window)
    (let ((frame (lem::get-frame-of-window prompt-window)))
      (when (eq prompt-window (frame-current-window frame))
        (let ((window (called-window prompt-window)))
          (setf (frame-current-window frame)
                (if (deleted-window-p window)
                    (first (window-list))
  
negative.code: (defclass prompt-window-parameters ()
    ((completion-function
      :initarg :completion-function
      :reader prompt-window-completion-function)
     (existing-test-function
      :initarg :existing-test-function
      :reader completion-window-existing-test-function)
     (called-window
      :initarg :called-window
      :reader prompt-window-called-window)
     (history
      :initarg :history
      :reader prompt-window-history)))
  
  (defclass prompt-window (floating-window prompt-window-parameters)
    ((start-point
  