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3 <title>MayaChemTools:Documentation:Parsers::Lexer.pm</title>
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13 <div class="DocNav">
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14 <table width="100%" border=0 cellpadding=0 cellspacing=2>
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15 <tr align="left" valign="top"><td width="33%" align="left"><a href="./PackageInfo.html" title="PackageInfo.html">Previous</a> <a href="./index.html" title="Table of Contents">TOC</a> <a href="./SimpleCalcParser.html" title="SimpleCalcParser.html">Next</a></td><td width="34%" align="middle"><strong>Parsers::Lexer.pm</strong></td><td width="33%" align="right"><a href="././code/Lexer.html" title="View source code">Code</a> | <a href="./../pdf/Lexer.pdf" title="PDF US Letter Size">PDF</a> | <a href="./../pdfgreen/Lexer.pdf" title="PDF US Letter Size with narrow margins: www.changethemargins.com">PDFGreen</a> | <a href="./../pdfa4/Lexer.pdf" title="PDF A4 Size">PDFA4</a> | <a href="./../pdfa4green/Lexer.pdf" title="PDF A4 Size with narrow margins: www.changethemargins.com">PDFA4Green</a></td></tr>
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16 </table>
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17 </div>
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18 <p>
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19 </p>
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20 <h2>NAME</h2>
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21 <p>Parsers::Lexer</p>
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22 <p>
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23 </p>
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24 <h2>SYNOPSIS</h2>
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25 <p>use Parsers::Lexer;</p>
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26 <p>use Parsers::Lexer qw(:all);</p>
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27 <p>
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28 </p>
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29 <h2>DESCRIPTION</h2>
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30 <p><strong>Lexer</strong> class provides the following methods:</p>
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31 <p> <a href="#new">new</a>, <a href="#getlex">GetLex</a>, <a href="#lex">Lex</a>, <a href="#next">Next</a>, <a href="#peek">Peek</a>, <a href="#stringifylexer">StringifyLexer</a>
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32 </p><p>The object oriented chained <strong>Lexer</strong> is implemented based on examples available in
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33 Higher-order Perl [ Ref 126 ] book by Mark J. Dominus. It is designed to be used
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34 both in standalone mode or as a base class for <strong>YYLexer</strong>.</p>
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35 <p>A chained lexer is created by generating a lexer for for the first specified token
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36 specification using specified input and chaining it with other lexers generated for all
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37 subsequent token specifications. The lexer generated for the first token specification
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38 uses input iterator to retrieve any available input text; the subsequent chained lexeres
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39 for rest of the token specifications use lexers generated for previous token
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40 specifications to get next input, which might be unmatched input text or a reference
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41 to an array containing token and matched text pair.</p>
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42 <p>
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43 </p>
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44 <h2>METHODS</h2>
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45 <dl>
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46 <dt><strong><a name="new" class="item"><strong>new</strong></a></strong></dt>
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47 <dd>
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48 <div class="OptionsBox">
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49 $Lexer = new Parsers::Lexer($Input, @TokensSpec);</div>
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50 <p>Using specified <em>Input</em> and <em>TokensSpec</em>, <strong>new</strong> method generates a new lexer
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51 and returns a reference to newly created <strong>Lexer</strong> object.</p>
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52 <p>Example:</p>
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53 <div class="OptionsBox">
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54 # Tokens specifications supplied by the caller. It's an array containing references
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55 <br/> # to arrays with each containing TokenLabel and TokenMatchRegex pair along with
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56 <br/> # an option reference to code to be executed after a matched.
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57 <br/> #
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58 <br/> @LexerTokensSpec = (
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59 <br/> [ 'LETTER', qr/[a-zA-Z]/ ],
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60 [ 'NUMBER', qr/\d+/ ],
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61 [ 'SPACE', qr/[ ]*/,
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62 <br/> sub { my($This, $TokenLabel, $MatchedText) = @_; return ''; }
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63 <br/> ],
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64 [ 'NEWLINE', qr/(?:\r\n|\r|\n)/,
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65 <br/> sub { my($This, $TokenLabel, $MatchedText) = @_; return "\n"; }
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66 <br/> ],
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67 [ 'CHAR', qr/./ ]
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68 <br/> );</div>
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69 <div class="OptionsBox">
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70 # Input string...
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71 <br/> $InputText = 'y = 3 + 4';
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72 <br/> $Lexer = new Parsers::Lexer($InputText, @LexerTokensSpec);</div>
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73 <div class="OptionsBox">
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74 # Process input stream...
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75 <br/> while (defined($Token = $Lexer->Lex())) {
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76 <br/> print "Token: " . ((ref $Token) ? "@{$Token}" : "$Token") . "\n";
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77 <br/> }</div>
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78 <div class="OptionsBox">
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79 # Input file...
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80 <br/> $InputFile = "Input.txt";
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81 <br/> open INPUTFILE, "$InputFile" or die "Couldn't open $InputFile: $!\n";
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82 <br/> $Lexer = new Parsers::Lexer(\*INPUTFILE, @LexerTokensSpec);</div>
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83 <div class="OptionsBox">
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84 # Input file iterator...
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85 <br/> $InputFile = "TestSimpleCalcParser.txt";
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86 <br/> open INPUTFILE, "$InputFile" or die "Couldn't open $InputFile: $!\n";
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87 <br/> $InputIterator = sub { return <INPUTFILE>; };
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88 <br/> $Lexer = new Parsers::Lexer($InputIterator, @LexerTokensSpec);</div>
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89 <div class="OptionsBox">
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90 @LexerTokensSpec = (
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91 <br/> [ 'VAR', qr/[[:alpha:]]+/ ],
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92 [ 'NUM', qr/\d+/ ],
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93 [ 'OP', qr/[-+=\/]/,
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94 <br/> sub { my($This, $Label, $Value) = @_;
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95 <br/> $Value .= "; ord: " . ord $Value;
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96 <br/> return [$Label, $Value];
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97 <br/> }
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98 <br/> ],
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99 [ 'NEWLINE', qr/(?:\r\n|\r|\n)/, sub { return [$_[1], 'NewLine']; } ],
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100 [ 'SPACE', qr/\s*/, sub { return [$_[1], 'Space']; } ],
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101 <br/> );</div>
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102 <div class="OptionsBox">
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103 # Look ahead without removing...
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104 <br/> $Token = $Lexer->Lex('Peek');
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105 <br/> if (defined $Token && ref $Token) {
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106 <br/> print "PEEK: Token: @{$Token}\n\n";
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107 <br/> }</div>
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108 <div class="OptionsBox">
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109 # Process input stream...
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110 <br/> while (defined($Token = $Lexer->Lex())) {
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111 <br/> print "Token: " . ((ref $Token) ? "@{$Token}" : "$Token") . "\n";
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112 <br/> }</div>
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113 </dd>
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114 <dt><strong><a name="getlex" class="item"><strong>GetLex</strong></a></strong></dt>
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115 <dd>
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116 <div class="OptionsBox">
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117 $LexerRef = $Lexer->GetLex();</div>
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118 <p>Returns a refernece to <em>Lexer</em> method to the caller for use in a specific <strong>YYLexer</strong>.</p>
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119 </dd>
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120 <dt><strong><a name="lex" class="item"><strong>Lex</strong></a></strong></dt>
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121 <dd>
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122 <div class="OptionsBox">
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123 $TokenRefOrText = $Lexer->Lex($Mode);
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124 <br/> if (ref $TokenRefOrText) {
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125 <br/> ($TokenLabel, $TokenValue) = @{$TokenRefOrText};
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126 <br/> }
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127 <br/> else {
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128 <br/> $TokenText = $TokenRefOrText;
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129 <br/> }</div>
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130 <p>Get next available token label and value pair as an array reference or unrecognized
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131 text from input stream by either removing it from the input or simply peeking ahead
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132 and without removing it from the input stream.</p>
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133 <p>Possible <em>Mode</em> values: <em>Peek, Next</em>. Default: <em>Next</em>.</p>
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134 </dd>
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135 <dt><strong><a name="next" class="item"><strong>Next</strong></a></strong></dt>
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136 <dd>
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137 <div class="OptionsBox">
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138 $TokenRefOrText = $Lexer->Next();</div>
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139 <p>Get next available token label and value pair as an array reference or unrecognized
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140 text from input stream by removing it from the input stream.</p>
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141 </dd>
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142 <dt><strong><a name="peek" class="item"><strong>Peek</strong></a></strong></dt>
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143 <dd>
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144 <div class="OptionsBox">
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145 $TokenRefOrText = $Lexer->Peek();</div>
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146 <p>Get next available token label and value pair as an array reference or unrecognized
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147 text from input stream by by simply peeking ahead and without removing it from the
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148 input stream.</p>
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149 </dd>
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150 <dt><strong><a name="stringifylexer" class="item"><strong>StringifyLexer</strong></a></strong></dt>
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151 <dd>
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152 <div class="OptionsBox">
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153 $LexerString = $Lexer->StringifyLexer();</div>
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154 <p>Returns a string containing information about <em>Lexer</em> object.</p>
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155 </dd>
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156 </dl>
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157 <p>
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158 </p>
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159 <h2>AUTHOR</h2>
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160 <p><a href="mailto:msud@san.rr.com">Manish Sud</a></p>
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161 <p>
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162 </p>
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163 <h2>SEE ALSO</h2>
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164 <p><a href="./YYLexer.html">YYLexer.pm</a>, <a href="./SimpleCalcYYLexer.html">SimpleCalcYYLexer.pm</a>, <a href="./SimpleCalcParser.html">SimpleCalcParser.yy</a>
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165 </p>
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166 <p>
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167 </p>
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168 <h2>COPYRIGHT</h2>
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169 <p>Copyright (C) 2015 Manish Sud. All rights reserved.</p>
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170 <p>This file is part of MayaChemTools.</p>
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171 <p>MayaChemTools is free software; you can redistribute it and/or modify it under
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172 the terms of the GNU Lesser General Public License as published by the Free
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173 Software Foundation; either version 3 of the License, or (at your option)
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174 any later version.</p>
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175 <p> </p><p> </p><div class="DocNav">
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176 <table width="100%" border=0 cellpadding=0 cellspacing=2>
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177 <tr align="left" valign="top"><td width="33%" align="left"><a href="./PackageInfo.html" title="PackageInfo.html">Previous</a> <a href="./index.html" title="Table of Contents">TOC</a> <a href="./SimpleCalcParser.html" title="SimpleCalcParser.html">Next</a></td><td width="34%" align="middle"><strong>March 29, 2015</strong></td><td width="33%" align="right"><strong>Parsers::Lexer.pm</strong></td></tr>
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178 </table>
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179 </div>
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