annotate doc/manual/xg-i.tex @ 0:13d2b8934445

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 \chapter{Exploring Your Grammar I: Traces}
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2
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3 \section{Introduction}
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4
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5 AnaGram provides two important facilities to help you become familiar
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6 with the workings of your parser: the File Trace and the Grammar
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7 Trace. The File Trace takes its input from a test file and, under
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8 your control, parses the input in accordance with your grammar. The
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9 Grammar Trace is completely interactive. In each state it presents
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10 you with a list of acceptable tokens and lets you select the one you
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11 wish. The File Trace lets you see how your grammar will deal with a
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12 specific input file. The Grammar Trace lets you answer ``what if?''
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13 questions.
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14
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15 AnaGram also provides several ready-made traces to help you deal with
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16 specific problems. The
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17 \index{Error Trace}\index{Trace}\index{Window}\agwindow{Error Trace}
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18 can show you why your parser has diagnosed a syntax error. The
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19 \index{Conflict Trace}\index{Trace}\index{Window}\agwindow{Conflict
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20 Trace} and
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21 \index{Reduction Trace}\index{Trace}\index{Window}\agwindow{Reduction
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22 trace} can help you identify the sources of ambiguities in your
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23 grammar. The
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24 \index{Keyword Anomaly Trace}\index{Trace}\index{Window}\agwindow{Keyword
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25 Anomaly Trace} can help you understand the genesis of a keyword
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26 anomaly in your grammar. In addition, the
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27 \index{Trace}\index{Auxiliary Trace}\index{Window}\agmenu{Auxiliary Trace}
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28 selection in the
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29 \agmenu{Auxiliary Windows} popup menu enables you to get a trace to
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30 any state you wish or to transmute a File Trace into a Grammar Trace.
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31
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32 The trace functions serve several purposes. They are an ideal way to
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33 learn how syntax directed parsing works since they make each step
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34 clearly visible. They are also useful in determining whether your
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35 grammar works as you wish it to. You can try your grammar out on real
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36 data before you actually build a parser. If your grammar has
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37 problems, such as conflicts, you can use the trace functions to track
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38 down the problems, to understand them, and to verify your corrections.
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39
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40 You may have any number of File and Grammar Traces active
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41 simultaneously.
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42
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43 Remember that AnaGram usually uses short-cut parsing actions whenever
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44 possible. If you wish to see just the standard four parsing actions,
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45 you may want to set the \agparam{traditional engine} switch. This
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46 will, however, substantially increase the size of your parser and
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47 reduce its performance.
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48
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49 \section{Trace Windows}
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50
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51 The \agwindow{File} and \agwindow{Grammar Trace} windows normally each
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52 contain three panes: the \agwindow{Parser Stack} pane, an input pane,
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53 and the \agwindow{Rule Stack} pane. If your grammar uses semantically
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54 determined productions, the Reduction Choices pane will appear when
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55 necessary to allow you to select a reduction token.
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56
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57 % XXX s/some point/a point/
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58 In the File Trace, the input, or \index{Test File pane}\agwindow{Test
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59 File}, pane displays the test file. You need only double click on
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60 some point in the pane to test your grammar up to that point in the
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61 file. Differently colored backgrounds are used to distinguish the
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62 part of the file that has been parsed from the part that has not yet
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63 been parsed.
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64
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65 In the Grammar Trace, the input, or \index{Allowable Input
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66 pane}\agwindow{Allowable Input}, pane displays a list of tokens which
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67 are allowable input in the current state of the parser. You may
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68 select tokens from the \agwindow{Allowable Input} pane, one by one, or
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69 use the text entry field to type input to be parsed.
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70
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71 The active pane has a distinctively colored title panel and cursor
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72 bar, except for the \agwindow{Test File} pane in the \agwindow{File
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73 Trace} which has no cursor bar. You can use the tab key to tab among
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74 the panes. The function of other keyboard keys depends on which pane
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75 is active.
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76
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77 Along the bottom of the trace windows is a toolbar which provides
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78 status information as well as control buttons.
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79
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80 \subsection{Parser Stack Pane}
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81
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82 The \index{Parser Stack pane}\agwindow{Parser Stack} pane, the upper
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83 left pane of the \agwindow{File Trace} and \agwindow{Grammar Trace}
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84 windows, displays the parser stack for the current trace.
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85
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86 Each line corresponds to one level in the parser state stack, showing
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87 the stack index, the parser state for that level, and the token which
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88 was seen at that state. The last line of the stack, the lookahead
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89 line, corresponds to the current state of the parser. Since no input
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90 has yet been processed for this state, the token, if any, which
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91 appears at this level is a lookahead token.
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92
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93 In the File Trace, the token on the lookahead line corresponds to the
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94 character at the parse location in the Test File pane. In the Grammar
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95 Trace, the lookahead line is empty whenever all previous input to the
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96 parser has been completely parsed, otherwise it will display the most
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97 recently selected input token.
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98
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99 If you move the cursor in the Parser Stack pane of a File Trace, the
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100 text that makes up the selected token will be highlighted in the Test
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101 File pane. You can back the parse up to any desired stack level by
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102 double clicking at the beginning of the token text in the Test File
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103 pane.
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104
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105 Similarly, if you move the cursor bar in the Parser Stack pane of a
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106 Grammar Trace, the \index{Allowable Input pane}\agwindow{Allowable
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107 Input} pane will change to display the allowable tokens in the
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108 selected state. The previously selected token will be highlighted.
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109 Then, double click on any token in the Allowable Input pane to back
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110 the parse up and choose a token a second time.
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111
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112 The \index{Rule Stack pane}\agwindow{Rule Stack} pane (see below) of
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113 the \agwindow{File} or \agwindow{Grammar Trace} is also synched to the
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114 \agwindow{Parser Stack} pane. If the syntax file window is visible,
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115 it will be synched to show the rule currently selected in the
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116 \agwindow{Rule Stack} pane. Note that rules that have been
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117 automatically generated by the expansion of virtual productions cannot
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118 be synched, so the top line of the syntax file will be highlighted
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119 instead.
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120
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121 If you right-click on a highlighted line in the Parser Stack pane, you
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122 will get a pop-up menu to give you more information. In particular
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123 you can get an \agwindow{Auxiliary Trace} starting at the current
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124 point in your \agwindow{File} or \agwindow{Grammar Trace}, so you can
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125 explore various possibilities without losing your position in the old
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126 trace.
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127
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128 \subsection{Rule Stack Pane}
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129
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130 The \index{Rule Stack pane}Rule Stack pane appears across the bottom
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131 of a \agwindow{Grammar Trace} or \agwindow{File Trace} window. It
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132 provides an alternate view of the parser stack for the trace, showing,
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133 for each state, rules instead of the tokens that you see in the
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134 \agwindow{Parser Stack} pane. Because it is synched with the syntax
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135 file window, the \agwindow{Rule Stack} makes it easy to see the
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136 relationship between the trace and your grammar.
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137
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138 For each level of the parser stack, the \agwindow{Rule Stack} shows
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139 the parser state number and all the active rules. The active rules at
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140 any state consist of all the expansion rules for the state that are
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141 consistent with the input at all subsequent states.
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142
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143 Except for the last level of the stack, each rule has a
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144 \index{Token}\agterm{marked token}, which in the default
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145 configuration is displayed in bold, italic type. The significance of
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146 the marked token is that all tokens in the rule to the left of the
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147 marked token have already been matched in the input, and the input in
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148 subsequent levels is consistent so far with the marked token. As more
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149 input is processed, rules that are inconsistent with the new input are
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150 deleted from the display.
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151
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152 The last level of the stack shows the current state of the parser and
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153 the rules against which the lookahead token will be matched. At this
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154 level, there may be rules with no marked tokens. These are rules
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155 which have been matched exactly in the input. If there is more than
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156 one such rule, at the next parser step the parser will use the
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157 lookahead token to determine which rule to reduce.
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158
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159 In the last level of the stack, marked tokens represent the input the
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160 parser expects to see next.
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161
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162 The \agwindow{Rule Stack} pane is synched with the syntax file window
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163 if it is visible so that the rule highlighted in the \agwindow{Rule
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164 Stack} can be seen in context in the syntax file. For rules that
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165 AnaGram generated automatically to implement virtual productions or
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166 the disregard statement, the cursor bar will move to the top of the
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167 syntax file window.
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168
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169 The \agwindow{Rule Stack} pane is also synched with the other panes in
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170 the trace. As you move the cursor bar in the \agwindow{Rule Stack},
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171 the cursor bar in the \agwindow{Parser Stack} pane will track the
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172 stack level in the \agwindow{Rule Stack}. In a \agwindow{File Trace},
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173 text will be highlighted in the \agwindow{Test File} pane
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174 corresponding to the selected token in the \agwindow{Parser Stack}
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175 pane. In a \agwindow{Grammar Trace}, the marked token in the
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176 highlighted rule will be highlighted in the \agwindow{Allowable Input}
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177 pane.
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178
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179 Clicking the right mouse button in the \agwindow{Rule Stack} pane pops
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180 up an \agmenu{Auxiliary Windows} menu to give you more information
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181 about the highlighted rule. The \agmenu{Auxiliary Windows} menu
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182 offers four choices keyed to the marked token: \agmenu{Expansion
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183 Rules}, \agmenu{Productions}, \agmenu{Set Elements} and \agmenu{Token
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184 Usage}. The \agmenu{Keywords}, \agmenu{State Definition} and
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185 \agmenu{State Expansion} options are keyed to the state number. The
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186 \agmenu{Expansion Chain} and \agmenu{Rule Context} options are keyed
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187 to the highlighted rule. Note that by the very nature of the rule
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188 stack, a completed rule may occur only at the last level.
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189
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190 \subsection{Reduction Choices Pane}
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191 \index{Reduction Choices pane}
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192
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193 The \agwindow{File Trace} and \agwindow{Grammar Trace} display a
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194 \agwindow{Reduction Choices} pane when they need to reduce a
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195 semantically determined production. The rule to be reduced is
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196 highlighted in the \agwindow{Rule Stack} pane. The syntax file
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197 window, if visible, will show this rule highlighted if it is one that
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198 appears directly in your grammar.
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199
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200 The \agwindow{Reduction Choices} pane lists all possible reduction
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201 tokens for the specified rule. The first reduction token that is
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202 admissible in the current context is highlighted and it appears as the
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203 lookahead token in the \agwindow{Parser Stack} pane. In the
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204 \agwindow{File Trace}, text that comprises the entire rule is
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205 highlighted in the \agwindow{Test File} pane.
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206
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207 Select the desired reduction token before continuing with the parse.
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208
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209 If you select a token and it does not appear as the lookahead token,
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210 it is not syntactically correct in the current context. If you try to
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211 proceed with the parse, you will get a selection error.
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212
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213 \subsection{Parse Status}
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214 \index{Parse Status}
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215
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216 Both the \agwindow{File} and \agwindow{Grammar Trace} have a
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217 \agwindow{Parse Status field} on the toolbar at the bottom of the
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218 window to indicate the current state of the parser. The possible
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219 values are as follows:
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220 \begin{itemize}
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221 \item \agmenu{Ready}: The parser is ready for input.
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222 \item \agmenu{Running}: The parser is processing input.
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223 \item \agmenu{Parse Complete}: According to the grammar, no further
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224 input is expected. Click on reset or reload to restart the parse.
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225 \item \agmenu{Syntax error}: A syntax error has been encountered. The
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226 parser cannot go any further.
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227 \item \agmenu{Unexpected end of file}: The parser has reached the end
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228 of the actual input but the grammar still expects more.
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229 \item \agmenu{Select reduction token}: The parser encountered a
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230 semantically determined production. Select a reduction token from the
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231 \agwindow{Reduction Choices} pane.
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232 \item \agmenu{Selection error}: The reduction token selected from the
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233 Reduction Choices pane was not allowable input in the present
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234 state. Select another reduction token.
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235 \end{itemize}
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236
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237
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238 \section{File Trace}
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239 \index{File Trace}\index{Trace}\index{Window}
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240
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241 \subsection{Starting File Trace}
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242
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243 To do a \agwindow{File Trace} you must first analyze the grammar you
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244 wish to use. Then select \agmenu{File Trace} from the \agmenu{Action}
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245 menu. Select a file for parsing and the trace will begin. If you
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246 have not analyzed a grammar or if your grammar does not accept ASCII
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247 characters the \agmenu{File Trace} option will be grayed out. You may
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248 provide a mask for the test file name by setting the
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249 \index{Test file mask}\index{Configuration parameters}\agparam{test
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250 file mask} configuration parameter in your syntax file (see Appendix
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251 A, Configuration Parameters). AnaGram normally reads test files in
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252 text mode, that is, carriage return characters are stripped. If you do
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253 not want carriage return characters removed, you should set the
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254 \index{Test file binary}\index{Configuration switches}\agparam{test
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255 file binary} configuration switch.
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256
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257 \subsection{Test File Pane}
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258
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259 The file under test is displayed in the input pane in the upper right
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260 of the \agwindow{File Trace} window. To parse to a specific point in
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261 the file, double click at that point. If you double click at a point
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262 that precedes the current parse location, the parse will back up to
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263 that point. You may also use the cursor keys to control the parse.
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264 As long as the parse location and the cursor are synchronized the
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265 parse will track the cursor when you move the cursor using the cursor
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266 keys.
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267
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268 If the parse encounters a syntax error, it will not be able to go
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269 beyond the location of the error. In this situation, moving the
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270 cursor right or down will cause the cursor position to differ from the
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271 parse location. The parse and cursor positions can also differ if you
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272 single click anywhere in the Test File pane.
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273
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274 If the parse location and the cursor are thus not synchronized, the
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275 \agmenu{Single Step} button will be replaced with a \index{Synch
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276 Parse}\agmenu{Synch Parse} button. Click on the \agmenu{Synch Parse}
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277 button to get the cursor and the parse back in synch. Of course, the
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278 parse will still not be able to proceed past a syntax error.
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279
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280 In the \agwindow{Test File} pane, you can distinguish text that has
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281 been parsed from unparsed text because it is shown in a different
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282 color. (The default background color for parsed text is lighter.)
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283 Initially no text has been parsed, and the caret is positioned at the
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284 beginning of the file. The \index{Parse Location}\agwindow{Parse
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285 Location} box at the lower left of \agwindow{File Trace} will show
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286 \textit{1:1} for line 1, column 1. The \agwindow{Parse Status} box
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287 next to it will say \agmenu{Ready}.
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288
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289 If your grammar uses semantically determined productions, the parse
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290 will halt when one is encountered and the \agwindow{Reduction Choices}
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291 pane will be displayed so you may select the appropriate reduction
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292 token.
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293
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294 % XXX index Reload?
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295 At any time you can click on the \index{Reset}\agmenu{Reset} button to
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296 reset the parse to the beginning of the test file. If you modify the
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297 test file, you can click on the \agmenu{Reload} button to load the
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298 modified file and reset the parse.
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299
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300 Normally, AnaGram reads test files in ``text'' mode, discarding
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301 carriage return characters. If your parser needs to recognize carriage
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302 return characters explicitly, you should turn the \index{test file
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303 binary}\agparam{test file binary} configuration switch on.
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304
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305 \subsection{File Trace Toolbar}
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306
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307 The File Trace window has a toolbar at the very bottom of the window
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308 which provides parse status information as described above and
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309 contains buttons to help control the parse. The buttons are as
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310 follows:
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311
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312 \begin{itemize}
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313 \item \index{Single Step}\agmenu{Single Step}: Advances the parse one
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314 parser action at a time.
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315 \item \index{Synch Parse}\agmenu{Synch Parse}: Replaces the \agmenu{Single
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316 Step} button when the blinking cursor and the parse location do not
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317 coincide. Clicking on the \agmenu{Synch Parse} button will cause the
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318 parse to back up to the blinking cursor, if the blinking cursor
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319 precedes the parse location, or parse to the blinking cursor
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320 otherwise. If the parser encounters a syntax error before reaching
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321 the cursor, the parse will stop at the error and the parse will still
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322 not be in synch with the cursor.
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323 \item \index{Parse File}\agmenu{Parse File}: Parses all the way to the
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324 end of file. The parse will not stop until it encounters a syntax
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325 error, a semantically determined production, or the end of file.
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326 \item \index{Reset}\agmenu{Reset}: Resets the parse to its initial
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327 state.
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328 \item \index{Reload}\agmenu{Reload}: Reloads the test file from
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329 disk. This is useful if you have edited the test file since you last
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330 loaded it into the \agwindow{File Trace}.
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331 \end{itemize}
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332
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333
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334 \section{Grammar Trace}
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335 \index{Grammar Trace}\index{Trace}\index{Window}
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336
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337 A \agwindow{Grammar Trace} can be selected from either the
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338 \agmenu{Action} menu or the \agwindow{Control Panel} toolbar. With
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339 it, you can examine the workings of your parser in detail. Using
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340 various options, you can set up representations of the
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341 \index{Parser state stack}\index{State stack}\index{Stack}parser state
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342 stack and parser state as they might appear in the course of execution
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343 of your parser. You can then examine the possible inputs and the
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344 changes to the state and the state stack caused by any input you
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345 choose.
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346
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347 Several of AnaGram's debugging facilities employ a ready-made
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348 \agwindow{Grammar Trace} to direct you to the source of trouble.
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349 These are the \agwindow{Conflict Trace}, the \agwindow{Reduction
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350 Trace}, the \agwindow{Error Trace}, the \agwindow{Keyword Anomaly
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351 Trace}, and the \agwindow{Auxiliary Trace}.
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352
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353 AnaGram now provides a text entry field where you can enter input text for a
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354 \agwindow{Grammar Trace}, in addition to choosing tokens from
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355 \agwindow{Allowable Input}. This means
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356 you can run a \agwindow{Grammar Trace} like a \agwindow{File Trace}
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357 where the test file is replaced by text you can type in. This is a
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358 very convenient way to check out your grammar.
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359
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360 \subsection{Allowable Input Pane}
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361 \index{Allowable Input pane}
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362
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363 The upper right pane of the \agwindow{Grammar Trace} window lists the
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364 allowable input tokens for the current state of the grammar. The
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365 current state is the state selected by the cursor bar in the
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366 \agwindow{Parser Stack} pane.
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367
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368 The tokens in the \agwindow{Allowable Input} pane are listed in two
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369 groups: first, the terminal tokens allowable in this state, and
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370 second, the nonterminal tokens. Between these two groups of tokens is
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371 inserted a line which is either an option for a default reduction, or
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372 declares that there is no default action.
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373
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374 Double click, press Enter, or click the \agmenu{Proceed} button to
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375 parse the highlighted token. When all parse actions triggered by the
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376 highlighted token have been completed, all panes of the trace will be
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377 redrawn to show the new state of the parser.
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378
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379 If you wish to see the results of a single parser action, click on the
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380 \agmenu{Single Step} button. The parser will perform a single parser
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381 action. If the token you selected was not shifted in, it will now be
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382 displayed as the lookahead token on the last line, the lookahead line,
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383 in the \agwindow{Parser Stack} pane, and will be preselected in the
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384 \agwindow{Allowable Input} pane. Because AnaGram, by default, uses a
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385 number of compound parser actions, this situation does not arise very
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386 often unless you have set the
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387 \index{traditional engine}\agparam{traditional engine} switch or reset
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388 the \index{default reductions}\agparam{default reductions} switch.
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389 Usually you will want to select the same token to proceed, but it is
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390 not necessary.
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391
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392 % XXX the << and >> render really poorly. They should be italic, too,
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393 % but I can't get them to set that way.
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394 The \agwindow{Allowable Input} pane also displays the parser action
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395 associated with a specific token, and its result, provided it is not a
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396 compound action. The parser action field for a token may be
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397 interpreted as follows: If this token would cause a shift to a new
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398 state, the action field is $>>$ followed by the new state number. If
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399 the token would cause a reduction, the action field is $<<$ followed
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400 by a rule number to show the rule reduced. If the parser action is a
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401 compound action, the action field is blank. If the token would cause
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402 the grammar to be accepted, the action field is \textit{Accept}.
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403
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404 If a parser action requires the reduction of a semantically determined
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405 production, the \agwindow{Reduction Choices} pane will open. Select a
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406 reduction token to continue.
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407
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408 Note that selecting a token in \agwindow{Allowable Input} can cause a
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409 syntax error under certain circumstances. This can happen only if the
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410 following conditions are all true:
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411
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412 \begin{itemize}
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413 \item the indicated operation is a reduction,
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414 \item the reduction token for the rule being reduced has been used in
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415 several different contexts in the grammar,
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416 \item and the specified token may follow it in some contexts and not
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417 in others.
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418 \end{itemize}
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419
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420 \subsection{Text Entry Field}
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421 \index{Text Entry field}
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422
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423 It is sometimes more convenient to enter text in the text entry field
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424 on the \agwindow{Grammar Trace} toolbar than to select individual
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425 tokens from the \agwindow{Allowable Input} pane. By entering text you
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426 can proceed quickly to the state you want without having to choose
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427 each individual token en route.
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428
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429 After entering text, press Enter or click on the \agmenu{Proceed}
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430 button to parse the text. The text will be parsed in its entirety
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431 unless a syntax error or semantically determined production is
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432 encountered.
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433
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434 Click on the \agmenu{Single Step} button to work slowly through the
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435 text step by step.
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436
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437 \subsection{Grammar Trace Toolbar}
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438
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439 The Grammar Trace window has a toolbar at the very bottom of the
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440 window which provides parse status information as described above and
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441 contains buttons to help control the parse. The buttons are as
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442 follows:
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443
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444 \begin{itemize}
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445 \item \index{Proceed}\agmenu{Proceed}: Parses the token selected in
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446 \agwindow{Reduction Choices} if that pane is active, or the token
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447 selected in \agwindow{Allowable Input} if that pane is active, or the
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448 content of the text entry field if that is active. The parse
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449 continues until the input has been entirely shifted in, a semantically
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450 determined production has been encountered, or a syntax error has
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451 been encountered.
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452 \item \index{Single Step}\agmenu{Single Step}: Advances the parse one
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453 parser action at a time. Input is taken as for the \agmenu{Proceed}
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454 button.
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455 \item \index{Reset}\agmenu{Reset}: Reset the parse to its initial
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456 state. This is especially useful if the \agwindow{Grammar Trace} is
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457 one of the pre-built traces discussed below. In such a trace the
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458 initial state can be quite complex.
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459 \end{itemize}
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460
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461
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462 \section{Other Traces}
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463
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464 \subsection{Error Trace}
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465 \index{Error Trace}\index{Trace}\index{Window}
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466
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467 An \agwindow{Error Trace} is a preset \agwindow{Grammar Trace}
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468 designed to help you deal with errors your parser encounters during
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469 operation. If the
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470 \index{Error trace}\index{Configuration switches}\agparam{error trace}
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471 configuration switch is set when AnaGram builds a parser, whenever the
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472 parser detects:
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473 \begin{itemize}
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474 \item a \index{Syntax error}\index{Errors}syntax error
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475 \item a parser stack overflow, or
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476 \item a reduction token error
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477 \end{itemize}
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478 it will write the current state stack to a file with the extension
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479 \index{etr}\index{File extension}\agfile{.etr} and the name of the
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480 parser file. If such a file already exists, it will be overwritten.
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481
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482 When you analyze the grammar, AnaGram will enable the \agmenu{Error
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483 Trace} option in the \agmenu{Browse} menu. When you select the
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484 \agmenu{Error Trace} option, you can select an error trace file.
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485 AnaGram will use it to create a grammar trace which reproduces the
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486 state of the parser at the time of the error. You may then work with
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487 the trace as with any other grammar trace. The \agmenu{Reset} button
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488 will restore the trace to its initial condition.
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489
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490 Note that when the syntax file is modified, an error trace file may
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491 become invalid. If you try to load an error trace file that is older
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492 than the syntax file, AnaGram will pop up a message box to warn you.
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493
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494 \subsection{Conflict and Reduction Traces}
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495 \index{Conflict Trace}\index{Trace}\index{Window}
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496 \index{Reduction Trace}\index{Trace}\index{Window}
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497
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498 The \agwindow{Conflict Trace} and its companion, the
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499 \agwindow{Reduction Trace}, are ready-made \agwindow{Grammar Traces}
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500 which can be invoked from a \agwindow{Conflicts} window or a
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501 \agwindow{Resolved Conflicts} window using the \agmenu{Auxiliary
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502 Windows} menu. The \agwindow{Conflict Trace} shows one way out of
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503 perhaps many ways to get to the conflict state highlighted in the
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504 \agwindow{Conflicts} window. The \agwindow{Reduction Trace}
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505 progresses one step farther than the \agwindow{Conflict Trace},
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506 showing the result of selecting a reduce action in the conflict state.
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507 You can manipulate both traces just as you would a regular grammar
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508 trace. The \agmenu{Reset} button will reset the trace to its original
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509 condition.
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510
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511 \agwindow{Conflict} and \agwindow{Reduction Trace} windows may be
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512 obtained only from the \agwindow{Conflicts} window or the
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513 \agwindow{Resolved Conflicts} window using the \agmenu{Auxiliary
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514 Windows} popup menu. For more information see the section on
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515 conflicts in Chapter 7.
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516
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517 \subsection{Keyword Anomaly Trace}
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518 \index{Keyword Anomaly Trace}\index{Trace}\index{Window}
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519
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520 The \agwindow{Keyword Anomaly Trace} is another ready-made grammar
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521 trace which is invoked from a \agwindow{Keyword Anomalies} window
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522 using the \agmenu{Auxiliary Windows} popup menu. It shows one way out
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523 of perhaps many to get to the anomaly highlighted in the
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524 \agwindow{Keyword Anomalies} window. You can manipulate the
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525 \agwindow{Keyword Anomaly Trace} in the same way that you would a
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526 regular grammar trace. The \agmenu{Reset} button will restore the
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527 trace to its original configuration.
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528
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529 The \agwindow{Keyword Anomaly Trace} may be obtained only from the
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530 \agmenu{Auxiliary Windows} popup menu in the \agwindow{Keyword
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531 Anomalies} window. For more information see the section on keyword
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532 anomalies in Chapter 7.
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533
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534 \subsection{Auxiliary Trace}
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535 \index{Auxiliary Trace}\index{Trace}
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536
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537 For many AnaGram windows, an \agwindow{Auxiliary Trace} is one of the
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538 options on the right mouse button pop up menu. In most cases this is
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539 simply a pre-built \agwindow{Grammar Trace} that leads to the state
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540 specified by the highlighted line in the window. In the case of the
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541 \agwindow{File} and \agwindow{Grammar Traces}, selecting an
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542 \agwindow{Auxiliary Trace} from the \agwindow{Parser Stack} pane popup
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543 menu gives you a \agwindow{Grammar Trace} with the same
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544 \agwindow{Parser Stack} pane as the original \agwindow{Trace}.
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545
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546 When using a \agwindow{File} or \agwindow{Grammar Trace}, an
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547 \agwindow{Auxiliary Trace} can be useful for comparing the results at
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548 a particular point of diverging input streams.
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549
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550
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551 \section{Trace Coverage}
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552 \index{Trace Coverage}\index{Window}\index{Coverage}
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553
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554 When you run either \agwindow{File Trace} or \agwindow{Grammar Trace},
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555 AnaGram counts the number of times each rule is reduced. You can
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556 display these counts by selecting the \agmenu{Trace Coverage} window
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557 in the \agmenu{Browse} menu. The window displays all of the rules in
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558 your grammar in the order in which they were encountered in your
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559 syntax file. The window is synched to your syntax file window so that
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560 you can easily see each rule in context. The first column of the
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561 table gives the number of times this rule has been reduced by the
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562 \agwindow{File Trace} process since you last analyzed your grammar.
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563 Note that if, when tracing a file, you back up and try a portion of
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564 input over and over, the counts for the rules involved will be
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565 inflated relative to the other rules in the grammar. Thus, the
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566 primary use of the \agwindow{Trace Coverage} table is to determine
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567 whether there are rules that are not tested at all. Because AnaGram
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568 normally uses a number of short-cut actions in its parsing tables,
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569 some rules will not be counted even though they are obviously found in
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570 the grammar. These rules all have length zero or one and have no
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571 reduction procedures. If you set the
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572 \index{rule coverage}\index{configuration parameters}\agparam{rule coverage}
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573 configuration switch, AnaGram will turn off some of the optimization
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574 so that you will get a more accurate count.
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575 % XXX shouldn't ``found in the grammar'' above be ``found in the input''?