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<center><h2>Class 14 Notes</h2></center>

<div class=reading>
<center>
<a href="../slides/class14-2x3.pdf">Lecture Slides, Suitable For Printing</a> 
</center> 
</div> 

<h3>Notes</h3>

<b>Places, Frames and Envrionments</b>
<ul>
<li> <em>Names</em> identify places.  <tt>(define <em>x</em>
<em>exp</em>)</tt> and <tt>(lambda (<em>x</em>) <em>exp</em>)</tt>
both create places named <tt><em>x</em></tt>.

<li> <em>Frames</em> hold names.  All names must be inside a frame.

<li> An <em>environment</em> contains a frame and a pointer to a parent enviornment.

<li> The <em>global environment</em> is the outermost
envirnoment.  The outermost frame contains all the Scheme primitives.
It has not parent.
</ul>
<pre>
   (define nextx






</pre>

Draw an environment that has multiple places named <tt>x</tt>:
<pre>







</pre>

<b>Compound Application Rule</b>
<ol>
<li> Construct a new environment whose parent is the environment the 
procedure's environment points to
<li> Make places in that frame with the names of each parameter that
contain the corresponding values of the operand expressions.
<li> Evaluate the body in the new environment
</ol>

<pre>
(define double 
   (lambda (x) (+ x x)))



(define nest 
  (lambda (x)
    (lambda (x)
      (+ x x))))

((nest 3) 4)
</pre>

<pre>
(define (evaluate-name name env)
   (if (null? env) (erro r)
       (if (frame-contains name (get-frame env))
               (lookup name (get-frame env))
           (evaluate-name name 
             (parent-environment 
                (get-frame env))))))
</pre>

How do we find the value associated with a name in an environment?
<p>
<p><br><p><br><p><br>

<h4>Golden Ages Links</h4>

<ul>
<li> <a href="http://www.radix.net/~bobg/books/great.html">Great Books of the
Western World</a> (How many were written in the last 15 years?  When was
the golden age of literature?)
<li> <a
href="http://maccentral.macworld.com/news/0101/09.personal.shtml">Steve
Jobs: Personal computer enters 'third golden age'</a>
<li> <a
href="http://www.cosmopolis.ch/english/cosmo19/two_golden_ages.htm"><em>Two
Golden Ages Masterpieces of Dutch and Danish Painting</em></a>
<li> Grade inflation articles (relate them to Tyson's essay): 
<a href="http://www.pilotonline.com/special/grades/index.html">
<em>Grade Inflation at Virginia Universities: Does A Stand for
Average?</em></a>, Virginia-Pilot, Sunday, 9 February 2003; 
Cavalier Daily,
<a href="http://www.cavalierdaily.com/CVArticle.asp?ID=15391&pid=987">
<em>
Making the Grade</em></a>, 19 March 2003 (the Cavalier Daily also
<a href="http://www.cavalierdaily.com/letters.asp?pid=990">published a
letter</a> on this subject). 

<li> <a
href="http://www.nytimes.com/2005/09/20/nyregion/20grades.html?oref=login"><em>
Students Receive Fewer A's, and Princeton Calls It Progress</em></a>,
New York Times, 20 September 2005.
</ul>

<div class="quote">
I am the student whose 3<sup>rd</sup> grade teacher wrote, "Neil should
cultivate a more serious attitude towards his school work."
<p>
I am also the student whose 6<sup>th</sup> grade home-room teacher
wrote, "Less social involvement and more academic diligence is in
order".
<p>
I also happen to be the student who, when he first took the SATs, got
500 in the verbal section. Allow me to remind you that a score of 500 is
exceptionally average. Remarkably ordinary. Undoubtedly
unremarkable. Well, five books and two magazine columns later, I
received a letter in the mail from the Educational Testing Service, the
creators and purveyors of the SAT. The letter asked my permission to
reprint a passage from one of my books for use in their verbal
exam. They were impressed with my writing style and compositional form,
and wanted to use the passage for the reading comprehension section of
their next exam. I did not know whether to be flattered or angry,
whether to kiss the letter or to burn it, or whether any single exam
should have any real meaning to anyone's life at all.
<p allign=right>
<a href="http://research.amnh.org/~tyson/StateDepartmentAward.php">
Neil deGrasse
Tyson</a>'s <a
href="http://research.amnh.org/users/tyson/speeches/StateDepartmentAward.html">Speech
at the State Department</a> to winners of the Presidential Award for
Excellence in Mathematics and Science Teaching

</div>


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