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annotate doc/misc/html/examples/hw.html @ 21:1c9dac05d040

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Add lint-style FALLTHROUGH annotations to fallthrough cases. (in the parse engine and thus the output code) Document this, because the old output causes warnings with gcc10.
author David A. Holland
date Mon, 13 Jun 2022 00:04:38 -0400 (2022-06-13)
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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