Used to detect the presence of a mouse. The value of RETURN-CODE is set to 1 if a mouse is available on the system. It is set to 0 if no mouse is present. (Takes no additional parameters.) Note that on character-based systems, the mouse must be enabled before its presence can be detected. So if you haven't enabled the mouse (see ENABLE-MOUSE above), RETURN-CODE will have a value of 0.