The exam that covers the Common Lisp material through Friday of this week is this coming Monday in EPS 108 from noon until 12:50 p.m. You may bring one 8.5 by 11 sheet of notes. The best way to practice for the exam is to work the daily exercises.

Material to Understand

CLOS stands for Common Lisp Object System. It is the Common Lisp mechanism that supports object oriented programming.
Declaring a Class. The class book inherits from no other classes. Each member of the class contains two data fields: pages and author. The pages to the left of :accessor is the internal field name. The pages to the right of :accessor is how you will access the internal field name. For simplicity, I always make these two names the same!
```
  (defclass book ()
    (
      (pages :accessor pages)
      (author :accessor author)
    )
  )
```
Instantiating a Class
```
  (setf my-book (make-instance 'book))
```

Accessing the Data Members

  (setf (pages my-book) 200)
  (setf (author my-book) 'Melville)

Writing a Method. defmethod stands for DEFine METHOD. Pretty-Print is a method that has one parameter, abook. The type of abook is specified to be an instance of book.
```
  (defmethod pretty-print ((abook book))
    (format t "The author of the book: ~a~%" (author abook))
    (format t "The number of pages: ~a~%" (pages abook))
  )
```
Calling a Method
```
  (pretty-print my-book)
```
Using Inheritance. Textbook is a subclass of book. It will inherit all the book methods and data members.
```
  (defclass textbook (book)
    (
      (subject :accessor subject)
    )
  )
```

Overriding Methods. To override the pretty-print method, simply redefine it with a more specific parameter type. In general, the most specific method that is applicable is the one that will be called.

  (defmethod pretty-print ((abook textbook))
    (format t "Pages: ~a~%" (pages abook))
    (format t "Author: ~a~%" (author abook))
    (format t "Subject: ~a~%" (subject abook))
  )

  (setf nillson (make-instance 'textbook))
  (setf (pages nillson) 513)
  (setf (author nillson) 'nillson)
  (setf (subject nillson) 'computer-science)

  (pretty-print nillson)   ;; calls the second version of pretty-print 
  (pretty-print my-book)   ;; calls the first version
  (pretty-print 100)       ;; ERROR, neither version is applicable

Exercises

Use CLOS to create a class called generic-list. This class should have methods called make-empty, is-empty, insert-item, and remove-item. Insert-item and remove-item should both operate from the front of the list.
Test the above methods to make sure that they work.
Add a class called stack. Have this class inherit as many of the generic-list methods as possible.
Add a class called queue. Have this class also inherit as many of the generic-list methods as possible.
Test the methods for stack and queue to make sure that they work.