The Debug window contains a listener (with a prompt) where you can enter and evaluate Lisp forms. It also displays debugging information after an error (click here to see that the description of the Debug window after an error). Here is the Debug window when there is no error being debugged:

The prompt is a
[current package](Number).
You can type directly to the prompt, pressing Enter
for a newline. If you have entered a complete Lisp expression,
pressing Enter evaluates it and the returned value is printed below
the entered form. If you have not entered a complete expression,
pressing Enter places the cursor on the next line, suitably indented,
waiting for more input.
The dropping outline to the right under the title bar displays the history of entered Lisp expressions, with the most recent visible.
The buttons to the left of the dropping outline work as follows. (Placing the cursor over a button causes the tooltip to display. We identify the buttons by the tooltip description.)
An additional listener pane can be created by choosing View | New Listener.
Common Graphics and IDE documentation is described in About Common Graphics and IDE documentation in cgide.htm.
The documentation is described in introduction.htm and the index is in index.htm.
Copyright (c) 1998-2000, Franz Inc. Berkeley, CA., USA. All rights reserved.
Created 2000.10.5.