使用CLOS构建的简单图书馆管理系统

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(defclass library-item ();CLASS LIBRARY-ITEM           ;the definition for class library-item
           ((title :reader title);it's read only
            (due-date :accessor ddate :initform nil :initarg :due-date)
            (patron :accessor pid :initform nil)))

;TEST FOR CLASS LIBRARY-ITEM

(setf (slot-value (make-instance 'library-item) 'title) "firstitem")
(setf (ddate (make-instance 'library-item)) '(1 2 3))
(setf myitem (make-instance 'library-item))
(setf (slot-value myitem 'title) "seconditem")
(setf (ddate myitem) '(1 2 3))
(list (title myitem)
      (ddate myitem)
      (pid myitem))

(defclass cd-dvd (library-item);CLASS CD-DVD                   ;the definition for class cd-dvd which is the subclass of library-item
  ((load-period :reader lp :initform 5)))
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;TEST FOR CLASS CD-DVD

(setf (slot-value (make-instance 'cd-dvd) 'title) "firstcd")
(setf (ddate (make-instance 'cd-dvd)) '(1 2 3))
(setf mycd (make-instance 'cd-dvd))
(setf (slot-value mycd 'title) "secondcd")
(setf (ddate mycd) '(1 2 3))
(list (title mycd)
      (ddate mycd)