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annotate doc/misc/html/examples/hw.html @ 16:f9e4689b837d

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Some minor updates for 15 years later.
author David A. Holland
date Tue, 31 May 2022 01:45:26 -0400
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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>Hello World!</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 <A HREF="../index.html">Index</A>
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17 <P>
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18 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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19 WIDTH=1010 HEIGHT=2 >
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20 <P>
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21
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22
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23 <H1>Hello, World!</H1>
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24
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25 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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26 WIDTH=1010 HEIGHT=2 >
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27
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28 <P>
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29 <H2>Introduction</H2>
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30 <P>
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31 Hello, world! has become the traditional first program to
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32 try in a new programming language. This directory provides
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33 two instances of "Hello, world!" The first, <tt>hw1</tt>, uses C. The
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34 second, <tt>hw2</tt>, uses C++.
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35 <P>
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36
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37 <H2>Hello, world! using C &nbsp;&nbsp;-&nbsp;&nbsp; HW1.SYN</H2>
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38 <tt>hw1</tt> accepts a single newline character as input and then
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39 prints the "Hello, world!" message on stdout.
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40 <P>
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41 Every grammar must have a single token, the grammar token,
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42 to which the entire grammar finally condenses. The default
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43 name for this token is "grammar", which is used here.
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44 <P>
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45 AnaGram productions use an arrow ( <CODE>-&gt;</CODE> ) to separate the
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46 token or tokens being described, on the left, from their
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47 descriptions, on the right. <tt>hw1</tt> consists of a single
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48 production, defining the token "grammar" to consist of a
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49 single newline character.
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50 <P>
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51 The right hand side of a production is called a "grammar
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52 rule" and in the general case consists of a series of rule
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53 elements separated by commas. Following the rule on the same
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54 line, introduced by an equal sign, there may be a "reduction
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55 procedure", C code to be executed when the rule is
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56 identified in the input stream. Here there is one rule
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57 element and the reduction procedure consists of a single C
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58 expression, followed by a semicolon.
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59 <P>
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60 Note that AnaGram permits comments in accordance with the
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61 rules for C comments. AnaGram comments, like C comments, do
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62 not ordinarily nest. However, you may set the "nest
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63 comments" configuration switch to allow nesting.
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64 <P>
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65 When AnaGram builds a parser, it will provide defaults for
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66 all important aspects of the parser which you do not
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67 specify. In <tt>hw1</tt>, there is no specification of input, so the
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68 parser will be set up to read characters one at a time from
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69 stdin.
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70 <P>
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71 If a syntax file contains no embedded C, AnaGram will
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72 automatically provide a main program to call the parser.
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73 Thus this simple grammar suffices to describe a complete
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74 program.
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75 <P>
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76
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77 <H2>Testing HW1</H2>
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78 To test <tt>hw1</tt>, run AnaGram and build a parser using
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79 <tt>hw1.syn</tt>.
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80 The name of the output source file will be <tt>hw1.c</tt>.
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81 Compile and link the
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82 parser with your C compiler. Then run it from the command line
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83 and press Enter.
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84 The "Hello, world!" message should appear on your screen.
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85 <P>
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86
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87 <H2>Hello, world! using C++ &nbsp;&nbsp;-&nbsp;&nbsp; HW2.SYN</H2>
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88 <tt>hw2</tt> is a step up in complexity. <tt>hw2</tt>
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89 creates a C++ program
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90 instead of C, and uses stream I/O to write the famous
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91 message.
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92 <P>
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93 The first complexity is the requirement to tell AnaGram to
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94 output a file with a C++ name rather than a C name.
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95 <!--
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96 Of
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97 course, this is a frill, since you could probably have
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98 compiled it anyway.
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99 -->
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100 The <b>parser file name</b> configuration
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101 parameter specifies that the name of the parser file should
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102 be the same as the name of the syntax file, but with the
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103 extension <tt>.cpp</tt>.
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104 <P>
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105 The second complexity is the need to provide an #include
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106 statement for <tt>iostream.h</tt> to get a definition of
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107 <tt>cout</tt>. <tt>hw1</tt>
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108 did not need to include <tt>stdio.h</tt>, since the parser
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109 always has
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110 an <CODE>#include</CODE> statement for <tt>stdio.h</tt> to
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111 support the default
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112 input procedures. To provide an <CODE>#include</CODE>
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113 statement, we need a
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114 block of embedded C.
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115 <P>
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116 Since we have a block of embedded C, AnaGram will not create
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117 a main program automatically. So we add a main program which
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118 does nothing but call the parser. The parser name is set (by
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119 default) to <tt>hw2</tt>.
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120 <P>
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121 Note also that in addition to C style comments, AnaGram also
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122 supports C++ style comments.
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123 <P>
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124
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125 <H2>Testing HW2</H2>
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126 To test <tt>hw2</tt>, build a parser using <tt>hw2.syn</tt>,
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127 just as you did
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128 for <tt>hw1</tt>. This time the name of the parser file will be
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129 <tt>hw2.cpp</tt>. Compile and link the parser with your C++ compiler.
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130 Then run it from the command line and press Enter. The
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131 "Hello, world!" message
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132 should appear on your screen.
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133 </P>
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134
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135 <BR>
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136 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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137 WIDTH=1010 HEIGHT=2 >
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138 <P>
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139 <IMG ALIGN="right" SRC="../images/pslrb6d.gif" ALT="Parsifal Software"
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140 WIDTH=181 HEIGHT=25>
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141 <BR CLEAR="right">
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142 <P>
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143 Back to <A HREF="../index.html">Index</A>
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144 <P>
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145 <ADDRESS><FONT SIZE="-1">
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146 AnaGram parser generator - examples<BR>
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147 Hello World!<BR>
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148 Copyright &copy; 1993-1999, Parsifal Software. <BR>
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149 All Rights Reserved.<BR>
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150 </FONT></ADDRESS>
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151
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152 </BODY>
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153 </HTML>
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154
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155