anchor.diff:  
       (person \"Common Lisp\" 33)
       => #.(PERSON \"Common Lisp\" 33)
  -
  -Convenient copier.
  -
  -    (defun birthday (person)
  -      (copy-person person :age (1+ (person-age person))))
  -
  -    (birthday *)
  -    => #.(PERSON \"Common Lisp\" 34)
   
   Pattern matching.
   
  
positive.code: 
  Without initialization.
  
  Printer.
  
      (defconstructor person
  
negative.code: some or all of its slots." type-name)
           (,type-name ,@slot-names))
  
         ;; Define a load form.
         (defmethod make-load-form ((self ,type-name) &optional env)
           (declare (ignore env))
           (list ',type-name
                 ,@(loop for reader in readers
                         collect `(,reader self))))
  
         (defmethod constructor-len ((x ,type-name))
           ,(length readers))
  
  