Classes defined by define-objc-class can be made to support Objective-C formal protocols by specifying the
class option. All the standard formal protocols from Mac OS X 10.4 are predefined.
Note: It is not possible to define new protocols entirely in Lisp on Mac OS X 10.5 and later, but existing protocols can be declared using the define-objc-protocol macro.
LispWorks Objective-C and Cocoa Interface User Guide and Reference Manual - 15 Dec 2011