objc:define-class

(objc:define-class "Name" "Superclass" methods &optional protocols)

Registers a class whose methods are Lisp functions. methods is a list of ("selector:" function) pairs; each function receives the receiver first, then the method's own arguments. A method's type comes from the superclass when it declares the selector, from an adopted protocol (protocols, a list of names) otherwise, and defaults to a target/action shape: no result, one object argument per colon. Re-defining a class rebinds its methods. Answers the class. Part of the macOS-only objc package -- the interpreter (java -jar, or the rontolisp native binary) and a compiled .class / .jar, never a .wasm; on a machine without the runtime it signals an error. See the macOS GUI guide.

CL-USER> (defvar *cls*
    (objc:define-class "MyTarget" "NSObject"
      (list (list "invoke:" (lambda (self sender) (print sender) nil)))))
CL-USER> (defvar *target* (objc:send (objc:send *cls* "alloc") "init"))
CL-USER> (objc:send button "setTarget:" *target*)
CL-USER> (objc:send button "setAction:" "invoke:")

The callback shapes are a closed set (no arguments; one or two object arguments; one object argument answering BOOL, an object or an integer); an error inside a callback is printed, not signalled.