txlyre
/
avram


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html401/loose.dtd">
<html>
<!-- Created on December 10, 2012 by texi2html 1.82
texi2html was written by: 
            Lionel Cons <[email protected]> (original author)
            Karl Berry  <[email protected]>
            Olaf Bachmann <[email protected]>
            and many others.
Maintained by: Many creative people.
Send bugs and suggestions to <[email protected]>
-->
<head>
<title>avram - a virtual machine code interpreter: 2.2 Concrete Syntax</title>

<meta name="description" content="avram - a virtual machine code interpreter: 2.2 Concrete Syntax">
<meta name="keywords" content="avram - a virtual machine code interpreter: 2.2 Concrete Syntax">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="texi2html 1.82">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
pre.display {font-family: serif}
pre.format {font-family: serif}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: serif; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: serif; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.roman {font-family:serif; font-weight:normal;}
span.sansserif {font-family:sans-serif; font-weight:normal;}
ul.toc {list-style: none}
-->
</style>


</head>

<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">

<a name="Concrete-Syntax"></a>
<table cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="Raw-Material.html#Raw-Material" title="Previous section in reading order"> &lt; </a>]</td>
<td valign="middle" align="left">[<a href="Bit-String-Encoding.html#Bit-String-Encoding" title="Next section in reading order"> &gt; </a>]</td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left">[<a href="Virtual-Machine-Specification.html#Virtual-Machine-Specification" title="Beginning of this chapter or previous chapter"> &lt;&lt; </a>]</td>
<td valign="middle" align="left">[<a href="Virtual-Machine-Specification.html#Virtual-Machine-Specification" title="Up section"> Up </a>]</td>
<td valign="middle" align="left">[<a href="Library-Reference.html#Library-Reference" title="Next chapter"> &gt;&gt; </a>]</td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left">[<a href="avram.html#Top" title="Cover (top) of document">Top</a>]</td>
<td valign="middle" align="left">[<a href="avram_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
<td valign="middle" align="left">[<a href="Function-Index.html#Function-Index" title="Index">Index</a>]</td>
<td valign="middle" align="left">[<a href="avram_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<hr size="1">
<a name="Concrete-Syntax-1"></a>
<h2 class="section">2.2 Concrete Syntax</h2>

<p>The previous section has developed a basic vocabulary for statements
such as &ldquo;the virtual machine code for the identity function is
<a name="index-identity-function"></a>
<code>(nil,(nil,nil))</code>&rdquo;, which are elaborated extensively in the
subsequent sections on code and data formats. However, a description in
this style would be inadequate without an explanation of how such an
entity as <code>(nil,(nil,nil))</code> is communicated to <code>avram</code> in a
virtual machine code file. The purpose of this section is to fill the
gap by explaining exactly how any given tree would be transformed to its
concrete representation.
</p>
<p>The syntax is based on a conversion of the trees to bit strings,
<a name="index-bit-strings"></a>
followed by grouping the bits into blocks of six, which are then encoded
by printable characters. Although anyone is free to modify <code>avram</code>,
it is recommended that the concrete syntax described here be maintained
for the sake of portability of virtual machine code applications.
</p>
<p>Building a tree by reading the data from a file requires a more
difficult algorithm than the one presented in this section, and is not
considered because it&rsquo;s not strictly necessary for a
compiler. Procedures for both reading and writing are available to C and
C++ users as part of the <code>avram</code> library, and are also easily
invoked on the virtual code level.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top"><a href="Bit-String-Encoding.html#Bit-String-Encoding">2.2.1 Bit String Encoding</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">         
</td></tr>
<tr><td align="left" valign="top"><a href="Blocking.html#Blocking">2.2.2 Blocking</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">                    
</td></tr>
</table>

<hr size="1">
<table cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="Raw-Material.html#Raw-Material" title="Previous section in reading order"> &lt; </a>]</td>
<td valign="middle" align="left">[<a href="Bit-String-Encoding.html#Bit-String-Encoding" title="Next section in reading order"> &gt; </a>]</td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left">[<a href="Virtual-Machine-Specification.html#Virtual-Machine-Specification" title="Beginning of this chapter or previous chapter"> &lt;&lt; </a>]</td>
<td valign="middle" align="left">[<a href="Virtual-Machine-Specification.html#Virtual-Machine-Specification" title="Up section"> Up </a>]</td>
<td valign="middle" align="left">[<a href="Library-Reference.html#Library-Reference" title="Next chapter"> &gt;&gt; </a>]</td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left">[<a href="avram.html#Top" title="Cover (top) of document">Top</a>]</td>
<td valign="middle" align="left">[<a href="avram_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
<td valign="middle" align="left">[<a href="Function-Index.html#Function-Index" title="Index">Index</a>]</td>
<td valign="middle" align="left">[<a href="avram_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<p>
 <font size="-1">
  This document was generated on <i>December 10, 2012</i> using <a href="http://www.nongnu.org/texi2html/"><i>texi2html 1.82</i></a>.
 </font>
 <br>

</p>
</body>
</html>