annotate doc/manual/pcb.tex @ 2:4b08ee1ecb99

Adjust install notes to clarify that Wine applies only to the Windows build. (Thanks to Perry Metzger for test-driving.)
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1 \chapter{Parser Control Block}
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2
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3 \index{PCB}\index{Parser control block}
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4 A \agterm{parser control block} is a structure which contains all of
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5 the data necessary to describe the instantaneous state of a parser.
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6 The \agcode{typedef} statement which defines the structure is included
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7 in the \index{Header file}\index{File}header file for your parser.
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8 AnaGram creates the name of the \index{Name}data type for the
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9 structure by appending \agcode{{\us}pcb{\us}type} to the parser name.
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10
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11 % XXX: does \index{Name} belong?
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12 If the
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13 \index{Declare pcb}\index{Configuration switches}\agparam{declare pcb}
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14 configuration switch is on, its default state, AnaGram will declare a
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15 parser control block for you at the beginning of your parser file.
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16 AnaGram will determine the \index{Name}name of the parser control
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17 block by appending \agcode{{\us}pcb} to the parser name. AnaGram will
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18 also define the macro \index{PCB}\index{Macros}\agcode{PCB} as a
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19 shorthand notation for use within the parser.
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20
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21 If you wish to declare your own parser control block, you must include
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22 the header file for your parser before your declaration. Then you
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23 declare a parser control block and define \agcode{PCB} to refer to the
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24 control block you have declared.
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25
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26 Suppose your grammar is called \agcode{widget}. You would then write
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27 the following statements in your embedded C in order to declare a
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28 parser control block named \agcode{widget{\us}control}:
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29
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30 \begin{indentingcode}{0.4in}
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31 \#include "widget.h"
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32 widget{\us}pcb{\us}type widget{\us}control;
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33 \#define PCB widget{\us}control
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34 \end{indentingcode}
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35
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36 The remainder of this appendix describes fields in the parser control
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37 block that may interest the user:
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38
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39 \index{column}\index{PCB}
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40 \paragraph{\agcode{int column;}}
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41 \agcode{PCB.column} keeps track of the column number of the current
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42 character in your input. Line and column numbers are tracked only if
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43 the \index{Lines and columns}\index{Configuration switches}
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44 \agparam{lines and columns} configuration switch has been set.
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45
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46 \index{cs}\index{PCB}
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47 \paragraph{\agcode{\textit{context-type} cs[];}}
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48 \agcode{PCB.cs} is your \index{Context stack}\index{Stack}context
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49 stack. \agcode{cs} will be defined only if you have assigned a value
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50 to the configuration parameter
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51 \index{Context type}\index{Configuration parameters}\agparam{context type}.
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52
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53 \index{error{\us}frame{\us}ssx}\index{PCB}
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54 \paragraph{\agcode{int error{\us}frame{\us}ssx;}}
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55 \agcode{PCB.error{\us}frame{\us}ssx} is a field to which your error handling
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56 routines may refer. When your
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57 \index{SYNTAX{\us}ERROR}\index{Macros}\agcode{SYNTAX{\us}ERROR} macro is
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58 called, if you have set both the
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59 \index{Diagnose errors}\index{Configuration switches}\agparam{diagnose errors}
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60 and
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61 \index{Error frame}\index{Configuration switches}\agparam{error frame}
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62 configuration switches,
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63 \agcode{PCB.error{\us}frame{\us}ssx} will contain the value of the parser
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64 stack index at the beginning of the frame token identified by
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65 \agcode{PCB.error{\us}frame{\us}token}. For example, if in a syntax file,
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66 you fail to close a comment, AnaGram will encounter an illegal end of
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67 file in the comment. In this situation, \agcode{error{\us}frame{\us}token} is
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68 the comment token, and \agcode{PCB.error{\us}frame{\us}ssx} gives the parser
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69 stack depth at the beginning of the comment.
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70
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71 \index{error{\us}frame{\us}token}\index{PCB}
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72 \paragraph{\agcode{int error{\us}frame{\us}token;}}
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73 \agcode{PCB.error{\us}frame{\us}token} is a field to which
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74 your error handling routines may refer. When your
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75 \index{SYNTAX{\us}ERROR}\index{Macros}\agcode{SYNTAX{\us}ERROR} macro is
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76 called, if you have set both
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77 \index{Diagnose errors}\index{Configuration switches}\agparam{diagnose errors}
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78 and
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79 \index{Error frame}\index{Configuration switches}\agparam{error frame},
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80 it will contain the token number of the frame token, a token which
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81 identifies the context of the error.
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82
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83 \index{error{\us}message}\index{PCB}
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84 \paragraph{\agcode{char *error{\us}message;}}
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85 \agcode{PCB.error{\us}message} is a field to which your error handling
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86 procedures may refer. If you have set the
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87 \index{Diagnose errors}\index{Configuration switches}\agparam{diagnose errors}
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88 configuration switch, on encountering a syntax error your parser will
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89 create a string containing an appropriate diagnostic message and store
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90 a pointer to it into \agcode{PCB.error{\us}message}.
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91
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92 \index{PCB}\index{exit{\us}flag}
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93 \paragraph{\agcode{int exit{\us}flag;}}
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94 \agcode{PCB.exit{\us}flag} contains a code value which indicates
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95 whether the parser is still running or whether it has terminated. If
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96 the parser has terminated, \agcode{PCB.exit{\us}flag} indicates the
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97 reason the parse has terminated. Mnemonic values for these \index{Exit
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98 codes}exit codes are defined in the header file for your parser. The
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99 values are as follows:
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100 % XXX s/mnemonic/symbolic/
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101
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102 \begin{tabular}{ll}
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103 \agcode{AG{\us}RUNNING{\us}CODE} & 0\\
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104 \agcode{AG{\us}SUCCESS{\us}CODE} & 1\\
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105 \agcode{AG{\us}SYNTAX{\us}ERROR{\us}CODE} & 2\\
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106 \agcode{AG{\us}REDUCTION{\us}ERROR{\us}CODE} & 3\\
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107 \agcode{AG{\us}STACK{\us}ERROR{\us}CODE} & 4\\
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108 \agcode{AG{\us}SEMANTIC{\us}ERROR{\us}CODE} & 5
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109 \end{tabular}
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110
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111 \index{PCB}\index{input{\us}code}
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112 \paragraph{\agcode{int input{\us}code;}}
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113 \agcode{PCB.input{\us}code} contains the current input character, or
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114 the token number, if your
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115 \index{GET{\us}INPUT}\index{Macros}\agcode{GET{\us}INPUT} macro supplies
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116 token numbers directly.
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117
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118 If you write your own \agcode{GET{\us}INPUT} macro, you must make sure
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119 that you store the input character or token number you get into
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120 \agcode{PCB.input{\us}code}.
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121
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122 If you have configured your parser to be
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123 \index{Event driven}\index{Configuration switches}\agparam{event driven},
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124 you must store the input character or token number for each token in
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125 turn into \agcode{PCB.input{\us}code} before you call your parser to
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126 process it.
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127
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128 \index{PCB}\index{input{\us}context}
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129 \paragraph{\agcode{\textit{context-type} input{\us}context;}}
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130 \agcode{PCB.input{\us}context} is a field which AnaGram adds to the
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131 definition of the parser control block structure when you assign a
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132 value to the
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133 \index{Context type}\index{Configuration parameters}\agparam{context type}
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134 configuration parameter. If you choose, you can
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135 write your \index{GET{\us}INPUT}\index{Macros}\agcode{GET{\us}INPUT} macro
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136 so that it stores the context value in \agcode{PCB.input{\us}context}.
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137 The default definition for
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138 \index{GET{\us}CONTEXT}\index{Macros}\agcode{GET{\us}CONTEXT} will
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139 then stack the context value at the appropriate time. You can think
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140 of \agcode{PCB.input{\us}context} as a sort of temporary ``parking
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141 place'' for the context value.
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142
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143 \index{PCB}\index{input{\us}value}
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144 \paragraph{\agcode{\textit{input-value-type} input{\us}value;}}
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145 \agcode{PCB.input{\us}value} is a field in the parser control block which
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146 is used to store the value of the input token.
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147
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148 If you write your own
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149 \index{Macros}\index{GET{\us}INPUT}\agcode{GET{\us}INPUT} macro or use
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150 \index{Event driven}\index{Configuration switches}\agparam{event driven}
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151 input, and you have set the
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152 \index{Input values}\index{Configuration switches}\agparam{input values}
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153 configuration switch, you should make sure that you store the value of
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154 the input character or token into \agcode{PCB.input{\us}value}.
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155
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156 \index{PCB}\index{line}
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157 \paragraph{\agcode{int line;}}
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158 \agcode{PCB.line} contains the line number of the current character in
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159 your input. Line and column numbers are tracked only if the
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160 \index{Lines and columns}\index{Configuration switches}
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161 \agparam{lines and columns} configuration switch has been set.
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162
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163 \index{PCB}\index{pointer}
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164 \paragraph{\agcode{\textit{pointer-type} pointer;}}
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165 \agcode{PCB.pointer} will be included in the parser control block for
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166 your parser if you have set the
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167 \index{Pointer input}\index{Configuration switches}\agparam{pointer input}
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168 configuration switch. The type of \agcode{PCB.pointer} is determined
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169 by the
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170 \index{Pointer type}\index{Configuration parameters}\agparam{pointer type}
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171 configuration parameter, which defaults to \agcode{unsigned char *}.
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172 Your main program should set \agcode{PCB.pointer} before it calls your
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173 parser. Thereafter, your parser will increment it appropriately.
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174 When you are executing a reduction procedure or a
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175 \index{SYNTAX{\us}ERROR}\index{Macros}\agcode{SYNTAX{\us}ERROR} macro
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176 \agcode{PCB.pointer} will always point to the next input character to
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177 be read.
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178
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179 \index{PCB}\index{reduction{\us}token}
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180 \paragraph{\agcode{int reduction{\us}token;}}
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181 Whenever your parser executes a reduction procedure,
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182 \agcode{PCB.reduction{\us}token} contains the number of the token to
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183 which the rule being reduced is to reduce to. If your grammar uses
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184 semantically determined productions, your reduction procedure may
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185 change the value of \agcode{PCB.reduction{\us}token} to the desired
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186 value.
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187
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188 Prior to calling your reduction procedure, your parser will set this
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189 field to the token number of the default reduction token, i.e., the
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190 first token in the reduction token list for the production being
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191 reduced. If the reduction procedure establishes that a different
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192 reduction token is appropriate, it should store the appropriate token
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193 number in \agcode{PCB.reduction{\us}token}. The easiest way to do this
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194 is to use the
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195 \index{CHANGE{\us}REDUCTION}\index{Macros}\agcode{CHANGE{\us}REDUCTION}
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196 macro.
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197
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198 \index{PCB}\index{sn}
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199 \paragraph{\agcode{int sn;}}
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200 \agcode{PCB.sn} always contains the current
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201 \index{State}\index{Number}state number of your parser.
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202
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203 \index{PCB}\index{ss}
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204 \paragraph{\agcode{int ss[];}}
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205 \agcode{PCB.ss} is the \index{Parser state stack}\index{State
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206 stack}\index{Stack}state stack for your parser. Before every shift action,
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207 the current state number, \agcode{PCB.sn}, is stored in
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208 \agcode{PCB.ss[PCB.ssx]}. \agcode{PCB.ssx} is then incremented.
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209
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210 \index{PCB}\index{ssx}
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211 \paragraph{\agcode{int ssx;}}
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212 \agcode{PCB.ssx} contains the parser \index{Stack}stack index for your
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213 parser. On every shift action it is incremented. On every reduction
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214 action the length of the grammar rule being reduced is subtracted from
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215 \agcode{PCB.ssx}.
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216
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217 \index{PCB}\index{token{\us}number}
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218 \paragraph{\agcode{int token{\us}number;}}
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219 \agcode{PCB.token{\us}number} contains the internal \index{Token
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220 number}\index{Number}token number of the current input token. If you
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221 are not supplying token numbers directly, it is the result of using
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222 the actual input character to index the token conversion array,
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223 \agcode{ag{\us}tcv}.
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224
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225 Your parser automatically maintains the proper value in
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226 \agcode{PCB.token{\us}number}. Input token numbers should always be
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227 stored in \agcode{PCB.input{\us}code}.
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228
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229 % XXX ``is a field is the''?
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230 \index{vs}\index{PCB}
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231 \paragraph{\agcode{\textit{value-stack-type} vs[];}}
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232 \agcode{PCB.vs} is a field is the
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233 \index{Parser value stack}\index{Stack}\index{Value stack}value stack
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234 for your parser. The semantic values of the tokens identified by the
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235 parser are stored in the value \index{Stack}\index{Value stack}stack.
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236 The value stack, like the other parser stacks, is indexed by
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237 \agcode{PCB.ssx}.
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238 When your parser is executing a reduction procedure,
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239 \agcode{PCB.vs[PCB.ssx]} contains the semantic value of the first
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240 token in the grammar rule you are reducing, \agcode{PCB.vs[PCB.ssx+1]}
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241 contains the second, and so forth. The return value from your
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242 reduction procedure will be stored in turn in
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243 \agcode{PCB.vs[PCB.ssx]}.
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244
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245 \index{{\us}dol{\us}vt}
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246 \agcode{PCB.vs} is defined to be of type \agcode{\${\us}vt}, where
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247 ``\agcode{\$}'' represents the name of your syntax file. AnaGram
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248 defines \agcode{\${\us}vt} so that it is large enough to store the
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249 semantic value of any of the tokens declared in your grammar.