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<center><h2>Class 15 Notes</h2></center>

<div class=reading>
<center>
<a href="../slides/class15-2x3.pdf">Lecture Slides, Suitable For Printing</a> 
</center> 
</div> 

<h3>Notes</h3>

<pre>
(define (make-counter)
   ((lambda (count)
      (lambda ()
        (set! count (+ 1 count))
        count))
   0))
</pre>

Draw the environment after: 
<pre>
   (define counter (make-counter))
   (counter)
</pre>
<p><br><p><br><p><br><p><br><p><br><p><br><p><br>
<p><br>

What is an <em>object</em>?
<p>
<p><br><p><br><p><br><p><br>

Why is it useful to package state and procedures together?
<p>
<p><br><p><br><p><br>

<b>Inheritance</b> is using the definition of one class to make another class.
<blockquote>
<pre>
</pre>
</blockquote>

The class <tt>TalkingDog</tt> <em>inherits</em> from <tt>Dog</tt>.<br>
<tt>TalkingDog</tt> is a <em>subclass</em> of <tt>Dog</tt>.<br>
The <em>superclass</em> of <tt>TalkingDog</tt> is <tt>Dog</tt>.
<p><br>

<p align=right>

<em>If I have seen further it is by standing
on the shoulders of giants.</em><br>
Isaac Newton (on inheritance?)
<p align=left>

<em>If I have not seen as far as others, it is because
giants were standing on my shoulders.</em><br>
Hal Abelson (on subtyping?)


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