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<center><h2>cs150: Notes 2</h2></center>

<h4>Assignments Due</h4>


<ul>
<li>18 January: <a href="/cs150/survey.html">Registration Survey</a> -
if you joined the class late and missed the deadline, please still
submit a survey now
<li>19 January (before Friday's class): Read Course Book Chapters 2 and
3, GEB, p. 3-41.
<li>22 January: <a href="/cs150/pledge.html">Pledge</a> (<em>read</em>
and sign)
<li>22 January: <a href="/cs150/ps/ps1/">Problem Set 1</a>
</ul>

<h4>Notes and Questions</h4>
<p>
What is a formal system?<br>
<p>
<p><br><p><br><p><br><p><br>

What is the difference between a formal system and a language?
<p>
<p><br><p><br><p><br><p><br>

Languages are made of:
<ul>
<li><b>Primitives</b> (almost all languages have these) - the simplest surface forms with meaning

<li><b>Means of Combination</b> (all languages have these) - rules of
production (ways to make new surface forms from ones you already have)

<li><b>Means of Abstraction</b> (all powerful languages have these) -
ways to use simple surface forms to represent complicated ones 
</ul>

When learning a foreign language, which of primitives, means of
combination or means of abstraction is hardest to learn?
<p>
<p><br><p><br>
<p>
Who was Admiral Grace Hopper and what did she do?
<p>
<p><br><p><br><p><br>
<p>

<b>Compiler:</b> A program that translates between two languages,
usually from a high-level programming language to machine code.
<p>

What is the difference between a compiler and an interpreter?

<p>
<p><br><p><br><p><br>
<p>

Why did John Backus want a precise way of describing languages?
<p><br><p><br>
<b>Backus Naur Form (BNF):</b> A way of describing the surface forms in a
language using replacement rules in the form:
<blockquote>
<em>non-terminal</em> <tt>::=</tt> <em>replacement</em>
</blockquote>
The rule means whenever you have what is on the left side of the
<tt>::=</tt>, you can replace it with what is on the right side.
<p>

What strings can the following BNF grammar produce?
<blockquote>
<tt><em>Sentence</em></tt> ::= <tt><em>Food</em> <em>Comparator</em> <em>Food</em></tt><br>
<tt><em>Food</em></tt> <tt>::=</tt> <b>Bodo's Bagels</b> <br>
<tt><em>Food</em></tt> <tt>::=</tt> <b>Krispy Kreme Donuts</b> <br>
<tt><em>Comparator</em></tt> <tt>::=</tt> <b>are better than</b> <br>
<tt><em>Comparator</em></tt> <tt>::=</tt> <b>are worse than</b>
</blockquote>

<p><br><p><br>

What strings can the following BNF grammar produce?
<blockquote>
<tt><em>Sentence</em></tt> ::= <b>I</b> <b>like</b> <tt><em>FoodList</em> </tt><br>
<tt><em>FoodList</em></tt> <tt>::=</tt> <tt><em>Food</em></tt><br>
<tt><em>FoodList</em></tt> <tt>::=</tt> <tt><em>Food</em></tt> <b>and</b> <tt><em>FoodList</em></tt><br>
<tt><em>Food</em></tt> <tt>::=</tt> <b>Bodo's Bagels</b> <br>
<tt><em>Food</em></tt> <tt>::=</tt> <b>Krispy Kreme Donuts</b> <br>
</blockquote>
<p><br><p><br>

<h4>
Links
</h4>

<ul>

<li><a href="http://ftp.arl.mil/~mike/comphist/eniac-story.html">ENIAC
Story</a> (like most ENIAC histories, it is <b>wrong</b> about ENIAC
being the "world's first electronic digital computer" &#151; we'll learn
why before PS4)

<li> 
<a href="http://www.hopper.navy.mil/">USS Hopper</a>
<li>
<a
href="http://www.chips.navy.mil/links/grace_hopper/file2.htm">
<em>Remembering
Grace Murray Hopper: A Legend in Her Own Time</em></a>, by Elizabeth
Dickason.

<li><a
href="http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Backus.html">John
Backus biography</a> 

<li>
<a href="http://gos.sbc.edu/j/jonesa.html">Keynote Speech, First Grace
 Hopper Conference</a> by <a
 href="http://www.cs.virginia.edu/jones/">Anita Jones</a>
</ul>

<font size="-1"><p align=right>
<em>I flunked out every year. I never studied. I hated studying. I was just
goofing around. It had the delightful consequence that every year I went
to summer school in New Hampshire where I spent the summer sailing and
having a nice time.</em><br>
John Backus (Since you probably don't get to spend the summer in New
Hampshire if you flunk out, you may not want to follow his advice here.)
</p>

<p align=right>
<em>
Frankly, we didn't have the vaguest idea how the things would work out
in detail... We struck out simply to optimze the object program, the
running time, because most people at that time believed you really
couldn't do that kind of thing.
</em><br>
John Backus (on FORTRAN language and compiler, quoted in 1966)


<p align=right>
<em>
"When I use a word," Humpty Dumpty said, in a rather scornful tone,
"it means just what I choose it to mean - nothing more nor less."
<br>
"The question is," said Alice,
"whether you can make words mean so many different things."<br>
"The question is," said Humpty Dumpty, "which is to be master that's all."
</em><br>
<a href="http://www.sabian.org/Alice/lgchap06.htm"><em>Through the
Looking Glass &mdash; Chapter VI: Humpty Dumpty</em></a>, Lewis Carroll
</font>

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<?
include('logos.php') ;

mt_srand( (double) microtime() * 1000000) ;

$first = mt_rand( 0, ($resTotal - 1) ) ;

print ("<table align=\"left\" bgcolor=\"white\"><tr><td align=\"center\">
<a href=\"http://www.cs.virginia.edu/~evans/cs150-fall2005/logos/\">");

print ( $res[$first] ) ;

print ("</td></tr></table>");

?>




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center cellpadding=6 cellspacing=2>
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<font size="-1">
<a href="http://www.cs.virginia.edu/~evans/cs150-fall2005/"><b>CS 150: Computer Science</b></a><br>
<a href="http://www.cs.virginia.edu/">University of Virginia</a><br>
</td>
<td align=right valign="bottom" width=25%>
<font size=-1>
<a href="mailto:evans@virginia.edu"><em>evans@virginia.edu</em></a><br>
<font size="-2"><a href="http://www.cs.virginia.edu/cs150-fall2005/reuse.html">Using these Materials</a></font>
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