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@@ -129,11 +129,13 @@ Cover art by Etienne Suvasa.
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@contents
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@node Top, Introduction, (dir), (dir)
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@ifnottex
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@node Top
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@top Bison
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@ifinfo
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This manual documents version @value{VERSION} of Bison.
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@end ifinfo
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This manual documents version @value{VERSION} of Bison, updated
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@value{UPDATED}.
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@end ifnottex
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@menu
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* Introduction::
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@@ -159,7 +161,7 @@ Reference sections:
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* Copying This Manual:: License for copying this manual.
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* Index:: Cross-references to the text.
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--- The Detailed Node Listing ---
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@detailmenu --- The Detailed Node Listing ---
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The Concepts of Bison
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@@ -301,9 +303,10 @@ Copying This Manual
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* GNU Free Documentation License:: License for copying this manual.
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@end detailmenu
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@end menu
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@node Introduction, Conditions, Top, Top
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@node Introduction
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@unnumbered Introduction
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@cindex introduction
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@@ -329,7 +332,7 @@ multi-character string literals and other features.
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This edition corresponds to version @value{VERSION} of Bison.
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@node Conditions, Copying, Introduction, Top
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@node Conditions
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@unnumbered Conditions for Using Bison
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As of Bison version 1.24, we have changed the distribution terms for
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@@ -359,7 +362,7 @@ using the other GNU tools.
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@include gpl.texi
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@node Concepts, Examples, Copying, Top
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@node Concepts
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@chapter The Concepts of Bison
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This chapter introduces many of the basic concepts without which the
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@@ -381,7 +384,7 @@ use Bison or Yacc, we suggest you start by reading this chapter carefully.
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* Grammar Layout:: Overall structure of a Bison grammar file.
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@end menu
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@node Language and Grammar, Grammar in Bison, , Concepts
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@node Language and Grammar
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@section Languages and Context-Free Grammars
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@cindex context-free grammar
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@@ -490,7 +493,7 @@ the grammar's start symbol. If we use a grammar for C, the entire input
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must be a `sequence of definitions and declarations'. If not, the parser
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reports a syntax error.
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@node Grammar in Bison, Semantic Values, Language and Grammar, Concepts
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@node Grammar in Bison
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@section From Formal Rules to Bison Input
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@cindex Bison grammar
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@cindex grammar, Bison
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@@ -535,7 +538,7 @@ stmt: RETURN expr ';'
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@noindent
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@xref{Rules, ,Syntax of Grammar Rules}.
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@node Semantic Values, Semantic Actions, Grammar in Bison, Concepts
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@node Semantic Values
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@section Semantic Values
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@cindex semantic value
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@cindex value, semantic
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@@ -577,7 +580,7 @@ semantic value that is a number. In a compiler for a programming
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language, an expression typically has a semantic value that is a tree
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structure describing the meaning of the expression.
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@node Semantic Actions, Locations Overview, Semantic Values, Concepts
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@node Semantic Actions
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@section Semantic Actions
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@cindex semantic actions
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@cindex actions, semantic
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@@ -608,7 +611,7 @@ expr: expr '+' expr @{ $$ = $1 + $3; @}
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The action says how to produce the semantic value of the sum expression
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from the values of the two subexpressions.
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@node Locations Overview, Bison Parser, Semantic Actions, Concepts
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@node Locations Overview
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@section Locations
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@cindex location
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@cindex textual position
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@@ -637,7 +640,7 @@ rule how @code{@@$} should be formed. When building a new location for a given
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grouping, the default behavior of the output parser is to take the beginning
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of the first symbol, and the end of the last symbol.
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@node Bison Parser, Stages, Locations Overview, Concepts
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@node Bison Parser
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@section Bison Output: the Parser File
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@cindex Bison parser
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@cindex Bison utility
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@@ -682,7 +685,7 @@ Therefore, you should avoid using C identifiers starting with @samp{yy}
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or @samp{YY} in the Bison grammar file except for the ones defined in
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this manual.
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@node Stages, Grammar Layout, Bison Parser, Concepts
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@node Stages
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@section Stages in Using Bison
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@cindex stages in using Bison
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@cindex using Bison
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@@ -724,7 +727,7 @@ Compile the code output by Bison, as well as any other source files.
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Link the object files to produce the finished product.
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@end enumerate
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@node Grammar Layout, , Stages, Concepts
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@node Grammar Layout
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@section The Overall Layout of a Bison Grammar
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@cindex grammar file
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@cindex file format
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@@ -767,7 +770,7 @@ definition of the lexical analyzer @code{yylex} goes here, plus subroutines
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called by the actions in the grammar rules. In a simple program, all the
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rest of the program can go here.
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@node Examples, Grammar File, Concepts, Top
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@node Examples
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@chapter Examples
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@cindex simple examples
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@cindex examples, simple
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@@ -796,7 +799,7 @@ to try them.
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* Exercises:: Ideas for improving the multi-function calculator.
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@end menu
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@node RPN Calc, Infix Calc, , Examples
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@node RPN Calc
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@section Reverse Polish Notation Calculator
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@cindex reverse polish notation
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@cindex polish notation calculator
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@@ -821,7 +824,7 @@ The source code for this calculator is named @file{rpcalc.y}. The
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* Comp: Rpcalc Compile. Run the C compiler on the output code.
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@end menu
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@node Rpcalc Decls, Rpcalc Rules, , RPN Calc
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@node Rpcalc Decls
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@subsection Declarations for @code{rpcalc}
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Here are the C and Bison declarations for the reverse polish notation
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@@ -861,7 +864,7 @@ arithmetic operators are designated by single-character literals, so the
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only terminal symbol that needs to be declared is @code{NUM}, the token
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type for numeric constants.
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@node Rpcalc Rules, Rpcalc Lexer, Rpcalc Decls, RPN Calc
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@node Rpcalc Rules
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@subsection Grammar Rules for @code{rpcalc}
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Here are the grammar rules for the reverse polish notation calculator.
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@@ -912,7 +915,7 @@ rule are referred to as @code{$1}, @code{$2}, and so on.
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* Rpcalc Expr::
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@end menu
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@node Rpcalc Input, Rpcalc Line, , Rpcalc Rules
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@node Rpcalc Input
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@subsubsection Explanation of @code{input}
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Consider the definition of @code{input}:
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@@ -946,7 +949,7 @@ The parser function @code{yyparse} continues to process input until a
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grammatical error is seen or the lexical analyzer says there are no more
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input tokens; we will arrange for the latter to happen at end of file.
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@node Rpcalc Line, Rpcalc Expr, Rpcalc Input, Rpcalc Rules
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@node Rpcalc Line
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@subsubsection Explanation of @code{line}
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Now consider the definition of @code{line}:
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@@ -971,7 +974,7 @@ uninitialized (its value will be unpredictable). This would be a bug if
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that value were ever used, but we don't use it: once rpcalc has printed the
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value of the user's input line, that value is no longer needed.
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@node Rpcalc Expr, , Rpcalc Line, Rpcalc Rules
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@node Rpcalc Expr
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@subsubsection Explanation of @code{expr}
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The @code{exp} grouping has several rules, one for each kind of expression.
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@@ -1030,7 +1033,7 @@ exp: NUM
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@noindent
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The latter, however, is much more readable.
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@node Rpcalc Lexer, Rpcalc Main, Rpcalc Rules, RPN Calc
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@node Rpcalc Lexer
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@subsection The @code{rpcalc} Lexical Analyzer
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@cindex writing a lexical analyzer
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@cindex lexical analyzer, writing
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@@ -1105,7 +1108,7 @@ yylex (void)
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@end group
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@end example
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@node Rpcalc Main, Rpcalc Error, Rpcalc Lexer, RPN Calc
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@node Rpcalc Main
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@subsection The Controlling Function
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@cindex controlling function
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@cindex main function in simple example
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@@ -1124,7 +1127,7 @@ main (void)
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@end group
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@end example
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@node Rpcalc Error, Rpcalc Gen, Rpcalc Main, RPN Calc
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@node Rpcalc Error
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@subsection The Error Reporting Routine
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@cindex error reporting routine
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@@ -1153,7 +1156,7 @@ have not written any error rules in this example, so any invalid input will
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cause the calculator program to exit. This is not clean behavior for a
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real calculator, but it is adequate for the first example.
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@node Rpcalc Gen, Rpcalc Compile, Rpcalc Error, RPN Calc
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@node Rpcalc Gen
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@subsection Running Bison to Make the Parser
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@cindex running Bison (introduction)
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@@ -1182,7 +1185,7 @@ Bison contains the source code for @code{yyparse}. The additional
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functions in the input file (@code{yylex}, @code{yyerror} and @code{main})
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are copied verbatim to the output.
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@node Rpcalc Compile, , Rpcalc Gen, RPN Calc
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@node Rpcalc Compile
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@subsection Compiling the Parser File
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@cindex compiling the parser
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@@ -1227,7 +1230,7 @@ example session using @code{rpcalc}.
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%
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@end example
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@node Infix Calc, Simple Error Recovery, RPN Calc, Examples
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@node Infix Calc
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@section Infix Notation Calculator: @code{calc}
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@cindex infix notation calculator
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@cindex @code{calc}
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@@ -1313,7 +1316,7 @@ Here is a sample run of @file{calc.y}:
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9
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@end example
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@node Simple Error Recovery, Multi-function Calc, Infix Calc, Examples
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@node Simple Error Recovery
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@section Simple Error Recovery
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@cindex error recovery, simple
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@@ -1355,7 +1358,7 @@ input lines; it would also have to discard the rest of the current line of
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input. We won't discuss this issue further because it is not specific to
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Bison programs.
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@node Multi-function Calc, Exercises, Simple Error Recovery, Examples
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@node Multi-function Calc
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@section Multi-Function Calculator: @code{mfcalc}
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@cindex multi-function calculator
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@cindex @code{mfcalc}
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@@ -1407,7 +1410,7 @@ Note that multiple assignment and nested function calls are permitted.
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* Symtab: Mfcalc Symtab. Symbol table management subroutines.
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@end menu
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@node Mfcalc Decl, Mfcalc Rules, , Multi-function Calc
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@node Mfcalc Decl
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@subsection Declarations for @code{mfcalc}
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Here are the C and Bison declarations for the multi-function calculator.
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@@ -1458,7 +1461,7 @@ just as @code{%token} is used for declaring token types. We have not used
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implicitly by the rules that define them. But @code{exp} must be declared
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explicitly so we can specify its value type. @xref{Type Decl, ,Nonterminal Symbols}.
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@node Mfcalc Rules, Mfcalc Symtab, Mfcalc Decl, Multi-function Calc
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@node Mfcalc Rules
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@subsection Grammar Rules for @code{mfcalc}
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Here are the grammar rules for the multi-function calculator.
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@@ -1492,7 +1495,7 @@ exp: NUM @{ $$ = $1; @}
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%%
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@end smallexample
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@node Mfcalc Symtab, , Mfcalc Rules, Multi-function Calc
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@node Mfcalc Symtab
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@subsection The @code{mfcalc} Symbol Table
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@cindex symbol table example
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@@ -1733,7 +1736,7 @@ This program is both powerful and flexible. You may easily add new
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functions, and it is a simple job to modify this code to install predefined
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variables such as @code{pi} or @code{e} as well.
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@node Exercises, , Multi-function Calc, Examples
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@node Exercises
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@section Exercises
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@cindex exercises
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@@ -1751,7 +1754,7 @@ Make the program report an error if the user refers to an
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uninitialized variable in any way except to store a value in it.
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@end enumerate
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@node Grammar File, Interface, Examples, Top
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@node Grammar File
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@chapter Bison Grammar Files
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|
|
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Bison takes as input a context-free grammar specification and produces a
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|
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@@ -1771,7 +1774,7 @@ The Bison grammar input file conventionally has a name ending in @samp{.y}.
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* Multiple Parsers:: Putting more than one Bison parser in one program.
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@end menu
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@node Grammar Outline, Symbols, , Grammar File
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@node Grammar Outline
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@section Outline of a Bison Grammar
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A Bison grammar file has four main sections, shown here with the
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@@ -1800,7 +1803,7 @@ Comments enclosed in @samp{/* @dots{} */} may appear in any of the sections.
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* C Code:: Syntax and usage of the additional C code section.
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@end menu
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@node C Declarations, Bison Declarations, , Grammar Outline
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@node C Declarations
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@subsection The C Declarations Section
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@cindex C declarations section
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@cindex declarations, C
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@@ -1813,7 +1816,7 @@ that they precede the definition of @code{yyparse}. You can use
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need any C declarations, you may omit the @samp{%@{} and @samp{%@}}
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delimiters that bracket this section.
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@node Bison Declarations, Grammar Rules, C Declarations, Grammar Outline
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@node Bison Declarations
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@subsection The Bison Declarations Section
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@cindex Bison declarations (introduction)
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@cindex declarations, Bison (introduction)
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@@ -1823,7 +1826,7 @@ terminal and nonterminal symbols, specify precedence, and so on.
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In some simple grammars you may not need any declarations.
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@xref{Declarations, ,Bison Declarations}.
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@node Grammar Rules, C Code, Bison Declarations, Grammar Outline
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@node Grammar Rules
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@subsection The Grammar Rules Section
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@cindex grammar rules section
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@cindex rules section for grammar
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@@ -1835,7 +1838,7 @@ There must always be at least one grammar rule, and the first
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@samp{%%} (which precedes the grammar rules) may never be omitted even
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if it is the first thing in the file.
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@node C Code, , Grammar Rules, Grammar Outline
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@node C Code
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@subsection The Additional C Code Section
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@cindex additional C code section
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@cindex C code, section for additional
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@@ -1856,7 +1859,7 @@ with @samp{yy} and many macros whose names start with @samp{YY}. It is a
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good idea to avoid using any such names (except those documented in this
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manual) in the additional C code section of the grammar file.
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@node Symbols, Rules, Grammar Outline, Grammar File
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@node Symbols
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@section Symbols, Terminal and Nonterminal
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@cindex nonterminal symbol
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@cindex terminal symbol
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@@ -1968,7 +1971,7 @@ The symbol @code{error} is a terminal symbol reserved for error recovery
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(@pxref{Error Recovery}); you shouldn't use it for any other purpose.
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In particular, @code{yylex} should never return this value.
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@node Rules, Recursion, Symbols, Grammar File
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@node Rules
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@section Syntax of Grammar Rules
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@cindex rule syntax
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@cindex grammar rule syntax
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@@ -2063,7 +2066,7 @@ expseq1: exp
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It is customary to write a comment @samp{/* empty */} in each rule
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with no components.
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@node Recursion, Semantics, Rules, Grammar File
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@node Recursion
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@section Recursive Rules
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@cindex recursive rule
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@@ -2132,7 +2135,7 @@ primary: constant
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defines two mutually-recursive nonterminals, since each refers to the
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other.
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@node Semantics, Locations, Recursion, Grammar File
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@node Semantics
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@section Defining Language Semantics
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@cindex defining language semantics
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@cindex language semantics, defining
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@@ -2156,7 +2159,7 @@ the numbers associated with @var{x} and @var{y}.
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action in the middle of a rule.
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@end menu
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@node Value Type, Multiple Types, , Semantics
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@node Value Type
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@subsection Data Types of Semantic Values
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@cindex semantic value type
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@cindex value type, semantic
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@@ -2178,7 +2181,7 @@ specify some other type, define @code{YYSTYPE} as a macro, like this:
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This macro definition must go in the C declarations section of the grammar
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file (@pxref{Grammar Outline, ,Outline of a Bison Grammar}).
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@node Multiple Types, Actions, Value Type, Semantics
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@node Multiple Types
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@subsection More Than One Value Type
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In most programs, you will need different data types for different kinds
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@@ -2202,7 +2205,7 @@ and for groupings with the @code{%type} Bison declaration (@pxref{Type
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Decl, ,Nonterminal Symbols}).
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@end itemize
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@node Actions, Action Types, Multiple Types, Semantics
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@node Actions
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@subsection Actions
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@cindex action
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@vindex $$
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@@ -2278,7 +2281,7 @@ As long as @code{bar} is used only in the fashion shown here, @code{$0}
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always refers to the @code{expr} which precedes @code{bar} in the
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definition of @code{foo}.
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@node Action Types, Mid-Rule Actions, Actions, Semantics
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@node Action Types
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@subsection Data Types of Values in Actions
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@cindex action data types
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@cindex data types in actions
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@@ -2323,7 +2326,7 @@ reference. For example, if you have defined types as shown here:
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then you can write @code{$<itype>1} to refer to the first subunit of the
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rule as an integer, or @code{$<dtype>1} to refer to it as a double.
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@node Mid-Rule Actions, , Action Types, Semantics
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@node Mid-Rule Actions
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@subsection Actions in Mid-Rule
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@cindex actions in mid-rule
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@cindex mid-rule actions
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@@ -2485,7 +2488,7 @@ the action is now at the end of its rule. Any mid-rule action can be
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converted to an end-of-rule action in this way, and this is what Bison
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actually does to implement mid-rule actions.
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@node Locations, Declarations, Semantics, Grammar File
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@node Locations
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@section Tracking Locations
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@cindex location
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@cindex textual position
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@@ -2506,7 +2509,7 @@ to take when rules are matched.
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* Location Default Action:: Defining a general way to compute locations.
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@end menu
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@node Location Type, Actions and Locations, , Locations
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@node Location Type
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@subsection Data Type of Locations
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@cindex data type of locations
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@cindex default location type
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@@ -2528,7 +2531,7 @@ struct
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@}
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@end example
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@node Actions and Locations, Location Default Action, Location Type, Locations
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@node Actions and Locations
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@subsection Actions and Locations
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@cindex location actions
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@cindex actions, location
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@@ -2595,7 +2598,7 @@ exp: @dots{}
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@end group
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@end example
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@node Location Default Action, , Actions and Locations, Locations
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@node Location Default Action
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@subsection Default Action for Locations
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@vindex YYLLOC_DEFAULT
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@@ -2639,7 +2642,7 @@ For consistency with semantic actions, valid indexes for the location array
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range from 1 to @var{n}.
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@end itemize
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@node Declarations, Multiple Parsers, Locations, Grammar File
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@node Declarations
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@section Bison Declarations
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@cindex declarations, Bison
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@cindex Bison declarations
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@@ -2668,7 +2671,7 @@ it explicitly (@pxref{Language and Grammar, ,Languages and Context-Free Grammars
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* Decl Summary:: Table of all Bison declarations.
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@end menu
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@node Token Decl, Precedence Decl, , Declarations
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@node Token Decl
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@subsection Token Type Names
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@cindex declaring token type names
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@cindex token type names, declaring
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@@ -2742,7 +2745,7 @@ interchangeably in further declarations or the grammar rules. The
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@code{yylex} function can use the token name or the literal string to
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obtain the token type code number (@pxref{Calling Convention}).
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@node Precedence Decl, Union Decl, Token Decl, Declarations
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@node Precedence Decl
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@subsection Operator Precedence
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@cindex precedence declarations
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@cindex declaring operator precedence
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@@ -2791,7 +2794,7 @@ When two tokens declared in different precedence declarations associate,
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the one declared later has the higher precedence and is grouped first.
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@end itemize
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@node Union Decl, Type Decl, Precedence Decl, Declarations
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@node Union Decl
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@subsection The Collection of Value Types
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@cindex declaring value types
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@cindex value types, declaring
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@@ -2822,7 +2825,7 @@ for a terminal or nonterminal symbol (@pxref{Type Decl, ,Nonterminal Symbols}).
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Note that, unlike making a @code{union} declaration in C, you do not write
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a semicolon after the closing brace.
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@node Type Decl, Expect Decl, Union Decl, Declarations
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@node Type Decl
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@subsection Nonterminal Symbols
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@cindex declaring value types, nonterminals
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@cindex value types, nonterminals, declaring
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@@ -2849,7 +2852,7 @@ use the same @code{<@var{type}>} construction in a declaration for the
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terminal symbol. All kinds of token declarations allow
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@code{<@var{type}>}.
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@node Expect Decl, Start Decl, Type Decl, Declarations
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@node Expect Decl
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@subsection Suppressing Conflict Warnings
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@cindex suppressing conflict warnings
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@cindex preventing warnings about conflicts
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@@ -2897,7 +2900,7 @@ Now Bison will stop annoying you about the conflicts you have checked, but
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it will warn you again if changes in the grammar result in additional
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conflicts.
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@node Start Decl, Pure Decl, Expect Decl, Declarations
|
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@node Start Decl
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@subsection The Start-Symbol
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@cindex declaring the start symbol
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@cindex start symbol, declaring
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@@ -2912,7 +2915,7 @@ may override this restriction with the @code{%start} declaration as follows:
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%start @var{symbol}
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@end example
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@node Pure Decl, Decl Summary, Start Decl, Declarations
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@node Pure Decl
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@subsection A Pure (Reentrant) Parser
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@cindex reentrant parser
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@cindex pure parser
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@@ -2952,7 +2955,7 @@ Whether the parser is pure has nothing to do with the grammar rules.
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You can generate either a pure parser or a nonreentrant parser from any
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valid grammar.
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@node Decl Summary, , Pure Decl, Declarations
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@node Decl Summary
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@subsection Bison Declaration Summary
|
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@cindex Bison declaration summary
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@cindex declaration summary
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@@ -3109,7 +3112,7 @@ The number of parser states (@pxref{Parser States}).
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@end table
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@end table
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@node Multiple Parsers,, Declarations, Grammar File
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|
@node Multiple Parsers
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@section Multiple Parsers in the Same Program
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Most programs that use Bison parse only one language and therefore contain
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@@ -3139,7 +3142,7 @@ of the parser source file, defining @code{yyparse} as
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@code{@var{prefix}parse}, and so on. This effectively substitutes one
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name for the other in the entire parser file.
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@node Interface, Algorithm, Grammar File, Top
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@node Interface
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|
|
@chapter Parser C-Language Interface
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@cindex C-language interface
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|
|
@cindex interface
|
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|
|
@@ -3161,7 +3164,7 @@ C code in the grammar file, you are likely to run into trouble.
|
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|
* Action Features:: Special features for use in actions.
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|
@end menu
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|
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|
@node Parser Function, Lexical, , Interface
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|
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|
|
@node Parser Function
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|
|
@section The Parser Function @code{yyparse}
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|
|
@findex yyparse
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|
|
@@ -3189,7 +3192,7 @@ Return immediately with value 0 (to report success).
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|
|
Return immediately with value 1 (to report failure).
|
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|
@end table
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|
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|
|
@node Lexical, Error Reporting, Parser Function, Interface
|
|
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|
|
@node Lexical
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|
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|
|
@section The Lexical Analyzer Function @code{yylex}
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|
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|
|
@findex yylex
|
|
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|
|
@cindex lexical analyzer
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|
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|
|
@@ -3218,7 +3221,7 @@ that need it. @xref{Invocation, ,Invoking Bison}.@refill
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in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}).
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|
@end menu
|
|
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|
|
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|
|
@node Calling Convention, Token Values, , Lexical
|
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|
|
@node Calling Convention
|
|
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|
|
@subsection Calling Convention for @code{yylex}
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|
|
The value that @code{yylex} returns must be the numeric code for the type
|
|
|
|
|
@@ -3295,7 +3298,7 @@ The @code{yytname} table is generated only if you use the
|
|
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|
|
@code{%token_table} declaration. @xref{Decl Summary}.
|
|
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|
|
@end itemize
|
|
|
|
|
|
|
|
|
|
@node Token Values, Token Positions, Calling Convention, Lexical
|
|
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|
|
@node Token Values
|
|
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|
|
@subsection Semantic Values of Tokens
|
|
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|
|
|
|
@vindex yylval
|
|
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|
|
@@ -3341,7 +3344,7 @@ then the code in @code{yylex} might look like this:
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|
@end group
|
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|
@end example
|
|
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|
|
@node Token Positions, Pure Calling, Token Values, Lexical
|
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|
|
@node Token Positions
|
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|
@subsection Textual Positions of Tokens
|
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|
|
@vindex yylloc
|
|
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|
|
@@ -3362,7 +3365,7 @@ feature makes the parser noticeably slower.
|
|
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|
|
@tindex YYLTYPE
|
|
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|
|
The data type of @code{yylloc} has the name @code{YYLTYPE}.
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|
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|
|
|
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|
|
@node Pure Calling, , Token Positions, Lexical
|
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|
@node Pure Calling
|
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|
@subsection Calling Conventions for Pure Parsers
|
|
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|
|
|
When you use the Bison declaration @code{%pure_parser} to request a
|
|
|
|
|
@@ -3469,7 +3472,7 @@ You can use @samp{%pure_parser} to request a reentrant parser without
|
|
|
|
|
also using @code{YYPARSE_PARAM}. Then you should call @code{yyparse}
|
|
|
|
|
with no arguments, as usual.
|
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|
|
@node Error Reporting, Action Features, Lexical, Interface
|
|
|
|
|
@node Error Reporting
|
|
|
|
|
@section The Error Reporting Function @code{yyerror}
|
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|
|
|
@cindex error reporting function
|
|
|
|
|
@findex yyerror
|
|
|
|
|
@@ -3529,7 +3532,7 @@ encountered so far. Normally this variable is global; but if you
|
|
|
|
|
request a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}) then it is a local variable
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|
|
|
which only the actions can access.
|
|
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|
@node Action Features, , Error Reporting, Interface
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|
@node Action Features
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|
|
@section Special Features for Use in Actions
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|
@cindex summary, action features
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|
|
@cindex action features summary
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|
@@ -3643,7 +3646,7 @@ Tracking Locations}.
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|
@end table
|
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|
@node Algorithm, Error Recovery, Interface, Top
|
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|
|
@node Algorithm
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|
|
@chapter The Bison Parser Algorithm
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|
|
@cindex Bison parser algorithm
|
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|
|
@cindex algorithm of parser
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|
|
@@ -3710,7 +3713,7 @@ This kind of parser is known in the literature as a bottom-up parser.
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|
|
* Stack Overflow:: What happens when stack gets full. How to avoid it.
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|
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|
|
@end menu
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|
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|
@node Look-Ahead, Shift/Reduce, , Algorithm
|
|
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|
|
@node Look-Ahead
|
|
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|
|
@section Look-Ahead Tokens
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|
|
@cindex look-ahead token
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|
@@ -3765,7 +3768,7 @@ doing so would produce on the stack the sequence of symbols @code{expr
|
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|
|
|
The current look-ahead token is stored in the variable @code{yychar}.
|
|
|
|
|
@xref{Action Features, ,Special Features for Use in Actions}.
|
|
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|
|
|
|
|
@node Shift/Reduce, Precedence, Look-Ahead, Algorithm
|
|
|
|
|
@node Shift/Reduce
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|
|
|
|
@section Shift/Reduce Conflicts
|
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|
|
|
@cindex conflicts
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|
|
@cindex shift/reduce conflicts
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|
|
@@ -3861,7 +3864,7 @@ expr: variable
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|
|
;
|
|
|
|
|
@end example
|
|
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|
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|
|
|
|
|
@node Precedence, Contextual Precedence, Shift/Reduce, Algorithm
|
|
|
|
|
@node Precedence
|
|
|
|
|
@section Operator Precedence
|
|
|
|
|
@cindex operator precedence
|
|
|
|
|
@cindex precedence of operators
|
|
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|
|
@@ -3878,7 +3881,7 @@ shift and when to reduce.
|
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|
|
* How Precedence:: How they work.
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|
|
@end menu
|
|
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|
|
|
|
@node Why Precedence, Using Precedence, , Precedence
|
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|
|
@node Why Precedence
|
|
|
|
|
@subsection When Precedence is Needed
|
|
|
|
|
|
|
|
|
|
Consider the following ambiguous grammar fragment (ambiguous because the
|
|
|
|
|
@@ -3925,7 +3928,7 @@ matter of whether the parser chooses to shift or reduce when the stack
|
|
|
|
|
contains @w{@samp{1 - 2}} and the look-ahead token is @samp{-}: shifting
|
|
|
|
|
makes right-associativity.
|
|
|
|
|
|
|
|
|
|
@node Using Precedence, Precedence Examples, Why Precedence, Precedence
|
|
|
|
|
@node Using Precedence
|
|
|
|
|
@subsection Specifying Operator Precedence
|
|
|
|
|
@findex %left
|
|
|
|
|
@findex %right
|
|
|
|
|
@@ -3946,7 +3949,7 @@ order in which they are declared. The first @code{%left} or
|
|
|
|
|
precedence is lowest, the next such declaration declares the operators
|
|
|
|
|
whose precedence is a little higher, and so on.
|
|
|
|
|
|
|
|
|
|
@node Precedence Examples, How Precedence, Using Precedence, Precedence
|
|
|
|
|
@node Precedence Examples
|
|
|
|
|
@subsection Precedence Examples
|
|
|
|
|
|
|
|
|
|
In our example, we would want the following declarations:
|
|
|
|
|
@@ -3972,7 +3975,7 @@ declared with @code{'-'}:
|
|
|
|
|
and so on. We assume that these tokens are more than one character long
|
|
|
|
|
and therefore are represented by names, not character literals.)
|
|
|
|
|
|
|
|
|
|
@node How Precedence, , Precedence Examples, Precedence
|
|
|
|
|
@node How Precedence
|
|
|
|
|
@subsection How Precedence Works
|
|
|
|
|
|
|
|
|
|
The first effect of the precedence declarations is to assign precedence
|
|
|
|
|
@@ -3993,7 +3996,7 @@ how each conflict was resolved.
|
|
|
|
|
Not all rules and not all tokens have precedence. If either the rule or
|
|
|
|
|
the look-ahead token has no precedence, then the default is to shift.
|
|
|
|
|
|
|
|
|
|
@node Contextual Precedence, Parser States, Precedence, Algorithm
|
|
|
|
|
@node Contextual Precedence
|
|
|
|
|
@section Context-Dependent Precedence
|
|
|
|
|
@cindex context-dependent precedence
|
|
|
|
|
@cindex unary operator precedence
|
|
|
|
|
@@ -4051,7 +4054,7 @@ exp: @dots{}
|
|
|
|
|
@end group
|
|
|
|
|
@end example
|
|
|
|
|
|
|
|
|
|
@node Parser States, Reduce/Reduce, Contextual Precedence, Algorithm
|
|
|
|
|
@node Parser States
|
|
|
|
|
@section Parser States
|
|
|
|
|
@cindex finite-state machine
|
|
|
|
|
@cindex parser state
|
|
|
|
|
@@ -4077,7 +4080,7 @@ There is one other alternative: the table can say that the look-ahead token
|
|
|
|
|
is erroneous in the current state. This causes error processing to begin
|
|
|
|
|
(@pxref{Error Recovery}).
|
|
|
|
|
|
|
|
|
|
@node Reduce/Reduce, Mystery Conflicts, Parser States, Algorithm
|
|
|
|
|
@node Reduce/Reduce
|
|
|
|
|
@section Reduce/Reduce Conflicts
|
|
|
|
|
@cindex reduce/reduce conflict
|
|
|
|
|
@cindex conflicts, reduce/reduce
|
|
|
|
|
@@ -4192,7 +4195,7 @@ redirects:redirect
|
|
|
|
|
;
|
|
|
|
|
@end example
|
|
|
|
|
|
|
|
|
|
@node Mystery Conflicts, Stack Overflow, Reduce/Reduce, Algorithm
|
|
|
|
|
@node Mystery Conflicts
|
|
|
|
|
@section Mysterious Reduce/Reduce Conflicts
|
|
|
|
|
|
|
|
|
|
Sometimes reduce/reduce conflicts can occur that don't look warranted.
|
|
|
|
|
@@ -4300,7 +4303,7 @@ return_spec:
|
|
|
|
|
;
|
|
|
|
|
@end example
|
|
|
|
|
|
|
|
|
|
@node Stack Overflow, , Mystery Conflicts, Algorithm
|
|
|
|
|
@node Stack Overflow
|
|
|
|
|
@section Stack Overflow, and How to Avoid It
|
|
|
|
|
@cindex stack overflow
|
|
|
|
|
@cindex parser stack overflow
|
|
|
|
|
@@ -4334,7 +4337,7 @@ You can control how much stack is allocated initially by defining the
|
|
|
|
|
macro @code{YYINITDEPTH}. This value too must be a compile-time
|
|
|
|
|
constant integer. The default is 200.
|
|
|
|
|
|
|
|
|
|
@node Error Recovery, Context Dependency, Algorithm, Top
|
|
|
|
|
@node Error Recovery
|
|
|
|
|
@chapter Error Recovery
|
|
|
|
|
@cindex error recovery
|
|
|
|
|
@cindex recovery from errors
|
|
|
|
|
@@ -4452,7 +4455,7 @@ value 1 when the parser is recovering from a syntax error, and 0 the
|
|
|
|
|
rest of the time. A value of 1 indicates that error messages are
|
|
|
|
|
currently suppressed for new syntax errors.
|
|
|
|
|
|
|
|
|
|
@node Context Dependency, Debugging, Error Recovery, Top
|
|
|
|
|
@node Context Dependency
|
|
|
|
|
@chapter Handling Context Dependencies
|
|
|
|
|
|
|
|
|
|
The Bison paradigm is to parse tokens first, then group them into larger
|
|
|
|
|
@@ -4471,7 +4474,7 @@ languages.
|
|
|
|
|
(Actually, ``kludge'' means any technique that gets its job done but is
|
|
|
|
|
neither clean nor robust.)
|
|
|
|
|
|
|
|
|
|
@node Semantic Tokens, Lexical Tie-ins, , Context Dependency
|
|
|
|
|
@node Semantic Tokens
|
|
|
|
|
@section Semantic Info in Token Types
|
|
|
|
|
|
|
|
|
|
The C language has a context dependency: the way an identifier is used
|
|
|
|
|
@@ -4546,7 +4549,7 @@ here the information is global, and is used for other purposes in the
|
|
|
|
|
program. A true lexical tie-in has a special-purpose flag controlled by
|
|
|
|
|
the syntactic context.
|
|
|
|
|
|
|
|
|
|
@node Lexical Tie-ins, Tie-in Recovery, Semantic Tokens, Context Dependency
|
|
|
|
|
@node Lexical Tie-ins
|
|
|
|
|
@section Lexical Tie-ins
|
|
|
|
|
@cindex lexical tie-in
|
|
|
|
|
|
|
|
|
|
@@ -4600,7 +4603,7 @@ the parser file is needed to make it accessible to the actions
|
|
|
|
|
(@pxref{C Declarations, ,The C Declarations Section}). You must also write the code in @code{yylex}
|
|
|
|
|
to obey the flag.
|
|
|
|
|
|
|
|
|
|
@node Tie-in Recovery, , Lexical Tie-ins, Context Dependency
|
|
|
|
|
@node Tie-in Recovery
|
|
|
|
|
@section Lexical Tie-ins and Error Recovery
|
|
|
|
|
|
|
|
|
|
Lexical tie-ins make strict demands on any error recovery rules you have.
|
|
|
|
|
@@ -4655,7 +4658,7 @@ make sure your error recovery rules are not of this kind. Each rule must
|
|
|
|
|
be such that you can be sure that it always will, or always won't, have to
|
|
|
|
|
clear the flag.
|
|
|
|
|
|
|
|
|
|
@node Debugging, Invocation, Context Dependency, Top
|
|
|
|
|
@node Debugging
|
|
|
|
|
@chapter Debugging Your Parser
|
|
|
|
|
@findex YYDEBUG
|
|
|
|
|
@findex yydebug
|
|
|
|
|
@@ -4737,7 +4740,7 @@ yyprint (FILE *file, int type, YYSTYPE value)
|
|
|
|
|
@}
|
|
|
|
|
@end smallexample
|
|
|
|
|
|
|
|
|
|
@node Invocation, Table of Symbols, Debugging, Top
|
|
|
|
|
@node Invocation
|
|
|
|
|
@chapter Invoking Bison
|
|
|
|
|
@cindex invoking Bison
|
|
|
|
|
@cindex Bison invocation
|
|
|
|
|
@@ -4783,7 +4786,7 @@ will produce @file{output.c++} and @file{outfile.h++}.
|
|
|
|
|
* VMS Invocation:: Bison command syntax on VMS.
|
|
|
|
|
@end menu
|
|
|
|
|
|
|
|
|
|
@node Bison Options, Environment Variables, , Invocation
|
|
|
|
|
@node Bison Options
|
|
|
|
|
@section Bison Options
|
|
|
|
|
|
|
|
|
|
Bison supports both traditional single-letter options and mnemonic long
|
|
|
|
|
@@ -4907,7 +4910,7 @@ Bison. If the grammar file is @file{foo.y}, the VCG output file will
|
|
|
|
|
be @file{foo.vcg}.
|
|
|
|
|
@end table
|
|
|
|
|
|
|
|
|
|
@node Environment Variables, Option Cross Key, Bison Options, Invocation
|
|
|
|
|
@node Environment Variables
|
|
|
|
|
@section Environment Variables
|
|
|
|
|
@cindex environment variables
|
|
|
|
|
@cindex BISON_HAIRY
|
|
|
|
|
@@ -4932,7 +4935,7 @@ also be specified or overridden in a similar fashion, with the
|
|
|
|
|
|
|
|
|
|
@end table
|
|
|
|
|
|
|
|
|
|
@node Option Cross Key, VMS Invocation, Environment Variables, Invocation
|
|
|
|
|
@node Option Cross Key
|
|
|
|
|
@section Option Cross Key
|
|
|
|
|
|
|
|
|
|
Here is a list of options, alphabetized by long option, to help you find
|
|
|
|
|
@@ -4976,7 +4979,7 @@ the corresponding short option.
|
|
|
|
|
@end example
|
|
|
|
|
@end ifinfo
|
|
|
|
|
|
|
|
|
|
@node VMS Invocation, , Option Cross Key, Invocation
|
|
|
|
|
@node VMS Invocation
|
|
|
|
|
@section Invoking Bison under VMS
|
|
|
|
|
@cindex invoking Bison under VMS
|
|
|
|
|
@cindex VMS
|
|
|
|
|
@@ -5004,7 +5007,7 @@ The VMS file system does not permit filenames such as
|
|
|
|
|
@file{foo.tab.c}. In the above example, the output file
|
|
|
|
|
would instead be named @file{foo_tab.c}.
|
|
|
|
|
|
|
|
|
|
@node Table of Symbols, Glossary, Invocation, Top
|
|
|
|
|
@node Table of Symbols
|
|
|
|
|
@appendix Bison Symbols
|
|
|
|
|
@cindex Bison symbols, table of
|
|
|
|
|
@cindex symbols in Bison, table of
|
|
|
|
|
@@ -5223,7 +5226,7 @@ Separates alternate rules for the same result nonterminal.
|
|
|
|
|
@xref{Rules, ,Syntax of Grammar Rules}.
|
|
|
|
|
@end table
|
|
|
|
|
|
|
|
|
|
@node Glossary, Copying This Manual, Table of Symbols, Top
|
|
|
|
|
@node Glossary
|
|
|
|
|
@appendix Glossary
|
|
|
|
|
@cindex glossary
|
|
|
|
|
|
|
|
|
|
@@ -5384,7 +5387,7 @@ grammatically indivisible. The piece of text it represents is a token.
|
|
|
|
|
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
|
|
|
|
|
@end table
|
|
|
|
|
|
|
|
|
|
@node Copying This Manual, Index, Glossary, Top
|
|
|
|
|
@node Copying This Manual
|
|
|
|
|
@appendix Copying This Manual
|
|
|
|
|
|
|
|
|
|
@menu
|
|
|
|
|
@@ -5393,7 +5396,7 @@ grammatically indivisible. The piece of text it represents is a token.
|
|
|
|
|
|
|
|
|
|
@include fdl.texi
|
|
|
|
|
|
|
|
|
|
@node Index, , Copying This Manual, Top
|
|
|
|
|
@node Index
|
|
|
|
|
@unnumbered Index
|
|
|
|
|
|
|
|
|
|
@printindex cp
|
|
|
|
|
|
Akim Demaille