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<center><h2>cs150: Notes 19</h2></center>

<h4>Assignments Due</h4>

<ul>
<li> Before <b>Friday, 30 February</b> (postponed from 21 February): Read 
<a href="http://research.amnh.org/~tyson/index.php">Neil DeGrasse
Tyson</a>'s <a href="/cs150/readings/tyson.pdf"><em>Science's Endless
Golden Age</em></a> (watching <a href="http://www.comedycentral.com/motherload/index.jhtml?ml_video=81508">Tyson's explanation of the
history of the universe</a> on <em>The Daily Show</em> is not required)
<li> <b>Wednesday, 14 March</b>: <a href="ps/ps5/">Problem Set 5</a>
<li> <b>Before Monday, 19 March</b>: Read rest of GEB part I (Chapters 2-4 and 6-9, in
addition to Chapters 1 and 5 you have already read). 
</ul>

<center>
<h4>GEB Study Guide</h4>
</center>

<p>

Your reading assignment for Spring Break (and the week after) is to
finish reading the first part of <em>G&ouml;del, Escher, Bach</em> (up
through and including Chapter IX).  The questions below might help you
think about the reading.  Then again, they might not.  I am quite
certain, however, that they will not help you prepare for the quiz that
will not be given on March 19.

<p>
Answer all the answerable questions, but unask the unanswerable ones.
This quiz will not be graded, but it won't be ungraded either. 
<p>

<b>1.</b> If you knew the answer to this question, what would it be?
<p>
<b>2.</b> Does this question have no answer?
<p>
<b>3.</b> Is the next question trickier than this one?
<p>
<b>4.</b> Was the previous question fairer than this one?
<p><p><br>
<b>5.</b> If this exam were graded, would your answer to the previous
question be different?
<p>
<b>6.</b> If this exam were graded, would your answer to the previous
question be different?
<p>
<b>6.</b> If this exam were graded, would your answer to the previous
question be different?
<p>
<b>7.</b> If you were G&ouml;del, how would you answer this?
<p>
<b>8.</b> Richard Feynman once said "If you think you know how
quantum mechanics works, you're wrong."   If Feynman were a logician instead,
would he have said "If you think you don't understand G&ouml;del's
Theorem, then you do." or "If you don't think you don't understand
G&ouml;del's Theorem, then you don't."?
<p>
<b>9.</b> If your final grade in CS150 depended only on your answer to
this question, would your answer to this question be different?
<p>
<b>10.</b> Ask and answer the question should I have asked instead of this one.
<p>
<b>11.</b> Ask and answer the question should I have asked instead of
the previous one.
<p>
<p><br><p><br>
<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>

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



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