LispWorks has a class browser. Its class library has several deep hierarchies with lots of classes. For example the class for a UI button is called CAPI:BUTTON.

LispWorks has a class browser. Its class library has several deep hierarchies with lots of classes. For example the class for a UI button is called CAPI:BUTTON. It has 11 CAPI superclasses and its depth for CAPI classes is six. It also has five subclasses adding more depth. The minute you write a GUI application in LispWorks, you'll use a macro called DEFINE-INTERFACE. What does it do? It creates a CLOS class for your application, which inherits from CAPI:INTERFACE. You want a new window pane type? Define a subclass of CAPI:OUTPUT-PANE. For another example: check the class hierarchy of stream classes in Clozure Common Lisp.