There is no concept of a 'primitive' type in Common Lisp. It handles type-checking for built-in types or for your own custom declared types. CL's type system is

There is no concept of a 'primitive' type in Common Lisp. It handles type-checking for built-in types or for your own custom declared types. CL's type system is very powerful. Here's a type-checking example related to CLOS : ;; High safety settings are required by SBCL for type checking of slots ;; See --> http://www.apl.jhu.edu/~hall/Lisp-Notes/Defclass.html (declaim (optimize (speed 0) (compilation-speed 0) (safety 3) (debug 3))) (defclass circle() ((center :type cons :accessor circle-center :initarg :center) (radius :type fixnum :accessor circle-radius :initarg :radius))) (defmethod circle-area ((x circle)) (* pi (expt (circle-radius x) 2))) (let ((c (make-instance 'circle :center '(0 0) :radius 4))) (format t "~A~%" (circle-area c)) (setf (circle-center c) '(2 3)) (setf (circle-radius c) 7) ;; this will fail at compile with a TYPE-ERROR ;(setf (circle-radius c) "B") ;; this will fail at compile with a UNDEFINED-FUNCTION ;; because the method does not exist ;(location c) )