+(deftype user-callback () '(or function symbol))
+
+(define-type-method alien-type ((type user-callback))
+ (declare (ignore type))
+ (alien-type 'pointer-data))
+
+(define-type-method to-alien-form ((type user-callback) func &optional copy-p)
+ (declare (ignore type copy-p))
+ `(register-callback-function ,func))
+
+