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Import AnaGram (near-)release tree into Mercurial.
author David A. Holland
date Sat, 22 Dec 2007 17:52:45 -0500
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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2 <HTML>
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3 <HEAD>
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4 <TITLE>Expression Evaluator - Macro preprocessor and C Parser </TITLE>
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5 </HEAD>
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6
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7
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8 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"
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9 TEXT="#000000" LINK="#0033CC"
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10 VLINK="#CC0033" ALINK="#CC0099">
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11
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12 <P>
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13 <IMG ALIGN="right" SRC="../../images/agrsl6c.gif" ALT="AnaGram"
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14 WIDTH=124 HEIGHT=30 >
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15 <BR CLEAR="all">
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16 Back to :
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17 <A HREF="../../index.html">Index</A> |
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18 <A HREF="index.html">Macro preprocessor overview</A>
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19 <P>
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20
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21
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22 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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23 WIDTH=1010 HEIGHT=2 >
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24 <P>
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25 <H1> Expression Evaluator - Macro preprocessor and C Parser </H1>
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26
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27 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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28 WIDTH=1010 HEIGHT=2 >
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29 <P>
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30 <BR>
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31
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32 <H2>Introduction</H2>
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33 <P> The Expression Evaluator module, <tt>ex.syn</tt>, exists only to
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34 evaluate the conditional expressions in <tt>#if</tt> and
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35 <tt>#elif</tt>
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36 statements. The syntax for these expressions has been
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37 extracted from a full C syntax and reduced to that which is
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38 necessary for this purpose.
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39 <P>
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40 The rules for the evaluation of constant expressions are
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41 given in Kernighan and Ritchie, sections A7.19 and A12.5
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42 <P>
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43 <BR>
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44
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45 <H2>Theory of Operation</H2>
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46 The only unusual feature of this grammar is the
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47 interposition of a token called "nonzero" to avoid division
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48 by zero. Otherwise the grammar is a conventional expression
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49 grammar.
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50 <P>
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51 The parser is implemented as an event driven parser. The
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52 initializer is <tt>init_ex()</tt>. The parser itself is
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53 <tt>ex()</tt>. The
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54 parser has been interfaced to the rest of the program by a
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55 class definition, <tt>expression_evaluator</tt>.
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56 <P>
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57 The class definition for <tt>expression_evaluator</tt> is given in
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58 <tt>mpp.h</tt>. Each instance of the class has its own parser control
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59 block. Therefore the parser makes all of its references
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60 indirectly through a pointer, <tt>ex_pcb</tt>. Whenever it is
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61 necessary to invoke <tt>init_ex()</tt> or <tt>ex()</tt>,
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62 therefore, it is
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63 necessary first to make sure <tt>ex_pcb</tt> is correctly set.
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64 <P>
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65 Input to the parser consists of tokens as defined in
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66 <tt>token.h</tt>. Since the input does not consist of simple
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67 characters, the <b>input values</b> switch is set. The input
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68 procedures store the full token into the input_value field
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69 of the pcb and the id field into input_code.
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70
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71 <P>
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72
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73 <BR>
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74
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75
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76 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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77 WIDTH=1010 HEIGHT=2 >
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78 <P>
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79 <IMG ALIGN="right" SRC="../../images/pslrb6d.gif" ALT="Parsifal Software"
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80 WIDTH=181 HEIGHT=25>
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81 <BR CLEAR="right">
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82
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83 <P>
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84 Back to :
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85 <A HREF="../../index.html">Index</A> |
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86 <A HREF="index.html">Macro preprocessor overview</A>
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87
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88 <P>
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89 <ADDRESS><FONT SIZE="-1">
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90 AnaGram parser generator - examples<BR>
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91 Expression Evaluator - Macro preprocessor and C Parser <BR>
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92 Copyright &copy; 1993-1999, Parsifal Software. <BR>
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93 All Rights Reserved.<BR>
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94 </FONT></ADDRESS>
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95
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96 </BODY>
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97 </HTML>
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98
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99