The LispWorks ORB product includes an IDL compiler that it uses to check and compile IDL files into Common Lisp fasl files. When the IDL file is processed by the preprocessor, it maps the IDL into Common Lisp. Appendix A: Common Lisp IDL Binding provides a specification for a standard mapping from CORBA IDL to Common Lisp.
According to this specification:
By including the IDL file in the defsystem, the application can access these mappings.
Developing Component Software with CORBA® - 01 Dec 2021 19:38:36