在 2020年1月3日 +0800 PM1:59，Eli Zaretskii <eliz@gnu.org>，写道：
How do you write a useful Lisp application for a thread if you have no
way of displaying any messages?
Workers are background workers. They don’t display messages directly. They post the error messages to the UI part of the lisp application.
For a lisp application such as an email client, it is splitted to two parts: the UI part and the worker part. The UI part may has two callbacks(or event handlers):
1. on_new_email
2. on_error
If the worker fetches an email successfully, it sends an event to the UI part and the on_new_email callback of the UI part will be called. If the worker fails, it sends an error to the UI part and the on_error callback will be called. The on_error callback can display the error message to user.