CL-USER> (defclass testclass () ((form  :initarg :form  :reader form)))
#<STANDARD-CLASS CL-USER::TESTCLASS>
CL-USER> (defmethod print-object ((obj testclass) stream)
       (print-unreadable-object (obj stream :type t)
         (format stream "FORM: ~A~%" (form obj))))
#<STANDARD-METHOD COMMON-LISP:PRINT-OBJECT (TESTCLASS T) {1002A77433}>
CL-USER> (make-instance 'testclass :form '(IN-PACKAGE #:MYPACKAGE))
#<TESTCLASS FORM: (IN-PACKAGE MYPACKAGE)
>
CL-USER>