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1
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1 NAME
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2 Parsers::Lexer
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3
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4 SYNOPSIS
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5 use Parsers::Lexer;
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6
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7 use Parsers::Lexer qw(:all);
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8
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9 DESCRIPTION
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10 Lexer class provides the following methods:
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11
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12 new, GetLex, Lex, Next, Peek, StringifyLexer
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13
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14 The object oriented chained Lexer is implemented based on examples
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15 available in Higher-order Perl [ Ref 126 ] book by Mark J. Dominus. It
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16 is designed to be used both in standalone mode or as a base class for
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17 YYLexer.
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18
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19 A chained lexer is created by generating a lexer for for the first
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20 specified token specification using specified input and chaining it with
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21 other lexers generated for all subsequent token specifications. The
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22 lexer generated for the first token specification uses input iterator to
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23 retrieve any available input text; the subsequent chained lexeres for
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24 rest of the token specifications use lexers generated for previous token
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25 specifications to get next input, which might be unmatched input text or
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26 a reference to an array containing token and matched text pair.
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27
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28 METHODS
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29 new
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30 $Lexer = new Parsers::Lexer($Input, @TokensSpec);
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31
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32 Using specified *Input* and *TokensSpec*, new method generates a new
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33 lexer and returns a reference to newly created Lexer object.
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34
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35 Example:
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36
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37 # Tokens specifications supplied by the caller. It's an array containing references
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38 # to arrays with each containing TokenLabel and TokenMatchRegex pair along with
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39 # an option reference to code to be executed after a matched.
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40 #
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41 @LexerTokensSpec = (
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42 [ 'LETTER', qr/[a-zA-Z]/ ],
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43 [ 'NUMBER', qr/\d+/ ],
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44 [ 'SPACE', qr/[ ]*/,
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45 sub { my($This, $TokenLabel, $MatchedText) = @_; return ''; }
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46 ],
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47 [ 'NEWLINE', qr/(?:\r\n|\r|\n)/,
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48 sub { my($This, $TokenLabel, $MatchedText) = @_; return "\n"; }
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49 ],
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50 [ 'CHAR', qr/./ ]
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51 );
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52
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53 # Input string...
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54 $InputText = 'y = 3 + 4';
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55 $Lexer = new Parsers::Lexer($InputText, @LexerTokensSpec);
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56
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57 # Process input stream...
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58 while (defined($Token = $Lexer->Lex())) {
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59 print "Token: " . ((ref $Token) ? "@{$Token}" : "$Token") . "\n";
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60 }
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61
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62 # Input file...
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63 $InputFile = "Input.txt";
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64 open INPUTFILE, "$InputFile" or die "Couldn't open $InputFile: $!\n";
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65 $Lexer = new Parsers::Lexer(\*INPUTFILE, @LexerTokensSpec);
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66
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67 # Input file iterator...
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68 $InputFile = "TestSimpleCalcParser.txt";
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69 open INPUTFILE, "$InputFile" or die "Couldn't open $InputFile: $!\n";
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70 $InputIterator = sub { return <INPUTFILE>; };
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71 $Lexer = new Parsers::Lexer($InputIterator, @LexerTokensSpec);
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72
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73 @LexerTokensSpec = (
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74 [ 'VAR', qr/[[:alpha:]]+/ ],
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75 [ 'NUM', qr/\d+/ ],
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76 [ 'OP', qr/[-+=\/]/,
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77 sub { my($This, $Label, $Value) = @_;
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78 $Value .= "; ord: " . ord $Value;
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79 return [$Label, $Value];
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80 }
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81 ],
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82 [ 'NEWLINE', qr/(?:\r\n|\r|\n)/, sub { return [$_[1], 'NewLine']; } ],
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83 [ 'SPACE', qr/\s*/, sub { return [$_[1], 'Space']; } ],
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84 );
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85
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86 # Look ahead without removing...
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87 $Token = $Lexer->Lex('Peek');
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88 if (defined $Token && ref $Token) {
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89 print "PEEK: Token: @{$Token}\n\n";
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90 }
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91
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92 # Process input stream...
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93 while (defined($Token = $Lexer->Lex())) {
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94 print "Token: " . ((ref $Token) ? "@{$Token}" : "$Token") . "\n";
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95 }
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96
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97 GetLex
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98 $LexerRef = $Lexer->GetLex();
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99
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100 Returns a refernece to *Lexer* method to the caller for use in a
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101 specific YYLexer.
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102
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103 Lex
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104 $TokenRefOrText = $Lexer->Lex($Mode);
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105 if (ref $TokenRefOrText) {
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106 ($TokenLabel, $TokenValue) = @{$TokenRefOrText};
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107 }
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108 else {
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109 $TokenText = $TokenRefOrText;
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110 }
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111
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112 Get next available token label and value pair as an array reference
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113 or unrecognized text from input stream by either removing it from
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114 the input or simply peeking ahead and without removing it from the
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115 input stream.
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116
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117 Possible *Mode* values: *Peek, Next*. Default: *Next*.
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118
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119 Next
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120 $TokenRefOrText = $Lexer->Next();
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121
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122 Get next available token label and value pair as an array reference
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123 or unrecognized text from input stream by removing it from the input
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124 stream.
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125
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126 Peek
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127 $TokenRefOrText = $Lexer->Peek();
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128
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129 Get next available token label and value pair as an array reference
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130 or unrecognized text from input stream by by simply peeking ahead
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131 and without removing it from the input stream.
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132
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133 StringifyLexer
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134 $LexerString = $Lexer->StringifyLexer();
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135
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136 Returns a string containing information about *Lexer* object.
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137
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138 AUTHOR
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139 Manish Sud <msud@san.rr.com>
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140
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141 SEE ALSO
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142 YYLexer.pm, SimpleCalcYYLexer.pm, SimpleCalcParser.yy
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143
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144 COPYRIGHT
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145 Copyright (C) 2015 Manish Sud. All rights reserved.
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146
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147 This file is part of MayaChemTools.
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148
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149 MayaChemTools is free software; you can redistribute it and/or modify it
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150 under the terms of the GNU Lesser General Public License as published by
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151 the Free Software Foundation; either version 3 of the License, or (at
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152 your option) any later version.
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153
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