Software Vault: The Gold Collection

home *** CD-ROM | disk | FTP | other *** search

/ Software Vault: The Gold Collection / Software Vault - The Gold Collection (American Databankers) (1993).ISO / cdr54 / bison118.zip / BISON.INF < prev next >

Wrap

Text File | 1993-06-01 | 38KB | 922 lines

Info file bison.info, produced by Makeinfo, -*- Text -*- from input file bison.texinfo. This file documents the Bison parser generator. Copyright (C) 1988, 1989, 1990 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "GNU General Public License" and "Conditions for Using Bison" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public License", "Conditions for Using Bison" and this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English. File: bison.info, Node: Semantic Tokens, Next: Lexical Tie-ins, Prev: Context Dependency, Up: Context Dependency Semantic Info in Token Types ============================ The C language has a context dependency: the way an identifier is used depends on what its current meaning is. For example, consider this: foo (x); This looks like a function call statement, but if `foo' is a typedef name, then this is actually a declaration of `x'. How can a Bison parser for C decide how to parse this input? The method used in GNU C is to have two different token types, `IDENTIFIER' and `TYPENAME'. When `yylex' finds an identifier, it looks up the current declaration of the identifier in order to decide which token type to return: `TYPENAME' if the identifier is declared as a typedef, `IDENTIFIER' otherwise. The grammar rules can then express the context dependency by the choice of token type to recognize. `IDENTIFIER' is accepted as an expression, but `TYPENAME' is not. `TYPENAME' can start a declaration, but `IDENTIFIER' cannot. In contexts where the meaning of the identifier is *not* significant, such as in declarations that can shadow a typedef name, either `TYPENAME' or `IDENTIFIER' is accepted--there is one rule for each of the two token types. This technique is simple to use if the decision of which kinds of identifiers to allow is made at a place close to where the identifier is parsed. But in C this is not always so: C allows a declaration to redeclare a typedef name provided an explicit type has been specified earlier: typedef int foo, bar, lose; static foo (bar); /* redeclare `bar' as static variable */ static int foo (lose); /* redeclare `foo' as function */ Unfortunately, the name being declared is separated from the declaration construct itself by a complicated syntactic structure--the "declarator". As a result, the part of Bison parser for C needs to be duplicated, with all the nonterminal names changed: once for parsing a declaration in which a typedef name can be redefined, and once for parsing a declaration in which that can't be done. Here is a part of the duplication, with actions omitted for brevity: initdcl: declarator maybeasm '=' init | declarator maybeasm ; notype_initdcl: notype_declarator maybeasm '=' init | notype_declarator maybeasm ; Here `initdcl' can redeclare a typedef name, but `notype_initdcl' cannot. The distinction between `declarator' and `notype_declarator' is the same sort of thing. There is some similarity between this technique and a lexical tie-in (described next), in that information which alters the lexical analysis is changed during parsing by other parts of the program. The difference is 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. File: bison.info, Node: Lexical Tie-ins, Next: Tie-in Recovery, Prev: Semantic Tokens, Up: Context Dependency Lexical Tie-ins =============== One way to handle context-dependency is the "lexical tie-in": a flag which is set by Bison actions, whose purpose is to alter the way tokens are parsed. For example, suppose we have a language vaguely like C, but with a special construct `hex (HEX-EXPR)'. After the keyword `hex' comes an expression in parentheses in which all integers are hexadecimal. In particular, the token `a1b' must be treated as an integer rather than as an identifier if it appears in that context. Here is how you can do it: %{ int hexflag; %} %% ... expr: IDENTIFIER | constant | HEX '(' { hexflag = 1; } expr ')' { hexflag = 0; $$ = $4; } | expr '+' expr { $$ = make_sum ($1, $3); } ... ; constant: INTEGER | STRING ; Here we assume that `yylex' looks at the value of `hexflag'; when it is nonzero, all integers are parsed in hexadecimal, and tokens starting with letters are parsed as integers if possible. The declaration of `hexflag' shown in the C declarations section of the parser file is needed to make it accessible to the actions (*note C Declarations::.). You must also write the code in `yylex' to obey the flag. File: bison.info, Node: Tie-in Recovery, Prev: Lexical Tie-ins, Up: Context Dependency Lexical Tie-ins and Error Recovery ================================== Lexical tie-ins make strict demands on any error recovery rules you have. *Note Error Recovery::. The reason for this is that the purpose of an error recovery rule is to abort the parsing of one construct and resume in some larger construct. For example, in C-like languages, a typical error recovery rule is to skip tokens until the next semicolon, and then start a new statement, like this: stmt: expr ';' | IF '(' expr ')' stmt { ... } ... error ';' { hexflag = 0; } ; If there is a syntax error in the middle of a `hex (EXPR)' construct, this error rule will apply, and then the action for the completed `hex (EXPR)' will never run. So `hexflag' would remain set for the entire rest of the input, or until the next `hex' keyword, causing identifiers to be misinterpreted as integers. To avoid this problem the error recovery rule itself clears `hexflag'. There may also be an error recovery rule that works within expressions. For example, there could be a rule which applies within parentheses and skips to the close-parenthesis: expr: ... | '(' expr ')' { $$ = $2; } | '(' error ')' ... If this rule acts within the `hex' construct, it is not going to abort that construct (since it applies to an inner level of parentheses within the construct). Therefore, it should not clear the flag: the rest of the `hex' construct should be parsed with the flag still in effect. What if there is an error recovery rule which might abort out of the `hex' construct or might not, depending on circumstances? There is no way you can write the action to determine whether a `hex' construct is being aborted or not. So if you are using a lexical tie-in, you had better 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. File: bison.info, Node: Debugging, Next: Invocation, Prev: Context Dependency, Up: Top Debugging Your Parser ********************* If a Bison grammar compiles properly but doesn't do what you want when it runs, the `yydebug' parser-trace feature can help you figure out why. To enable compilation of trace facilities, you must define the macro `YYDEBUG' when you compile the parser. You could use `-DYYDEBUG=1' as a compiler option or you could put `#define YYDEBUG 1' in the C declarations section of the grammar file (*note C Declarations::.). Alternatively, use the `-t' option when you run Bison (*note Invocation::.). We always define `YYDEBUG' so that debugging is always possible. The trace facility uses `stderr', so you must add `#include <stdio.h>' to the C declarations section unless it is already there. Once you have compiled the program with trace facilities, the way to request a trace is to store a nonzero value in the variable `yydebug'. You can do this by making the C code do it (in `main', perhaps), or you can alter the value with a C debugger. Each step taken by the parser when `yydebug' is nonzero produces a line or two of trace information, written on `stderr'. The trace messages tell you these things: * Each time the parser calls `yylex', what kind of token was read. * Each time a token is shifted, the depth and complete contents of the state stack (*note Parser States::.). * Each time a rule is reduced, which rule it is, and the complete contents of the state stack afterward. To make sense of this information, it helps to refer to the listing file produced by the Bison `-v' option (*note Invocation::.). This file shows the meaning of each state in terms of positions in various rules, and also what each state will do with each possible input token. As you read the successive trace messages, you can see that the parser is functioning according to its specification in the listing file. Eventually you will arrive at the place where something undesirable happens, and you will see which parts of the grammar are to blame. The parser file is a C program and you can use C debuggers on it, but it's not easy to interpret what it is doing. The parser function is a finite-state machine interpreter, and aside from the actions it executes the same code over and over. Only the values of variables show where in the grammar it is working. The debugging information normally gives the token type of each token read, but not its semantic value. You can optionally define a macro named `YYPRINT' to provide a way to print the value. If you define `YYPRINT', it should take three arguments. The parser will pass a standard I/O stream, the numeric code for the token type, and the token value (from `yylval'). Here is an example of `YYPRINT' suitable for the multi-function calculator (*note Mfcalc Decl::.): #define YYPRINT(file, type, value) yyprint (file, type, value) static void yyprint (file, type, value) FILE *file; int type; YYSTYPE value; { if (type == VAR) fprintf (file, " %s", value.tptr->name); else if (type == NUM) fprintf (file, " %d", value.val); } File: bison.info, Node: Invocation, Next: Table of Symbols, Prev: Debugging, Up: Top Invoking Bison ************** The usual way to invoke Bison is as follows: bison INFILE Here INFILE is the grammar file name, which usually ends in `.y'. The parser file's name is made by replacing the `.y' with `.tab.c'. Thus, the `bison foo.y' filename yields `foo.tab.c', and the `bison hack/foo.y' filename yields `hack/foo.tab.c'. Bison supports both traditional single-letter options and mnemonic long option names. Long option names are indicated with `--' instead of `-'. Abbreviations for option names are allowed as long as they are unique. When a long option takes an argument, like `--file-prefix', connect the option name and the argument with `='. Here is a list of options that can be used with Bison, alphabetized by short option. It is followed by a cross key alphabetized by long option. `-b FILE-PREFIX' `--file-prefix=PREFIX' Specify a prefix to use for all Bison output file names. The names are chosen as if the input file were named `PREFIX.c'. `-d' `--defines' Write an extra output file containing macro definitions for the token type names defined in the grammar and the semantic value type `YYSTYPE', as well as a few `extern' variable declarations. If the parser output file is named `NAME.c' then this file is named `NAME.h'. This output file is essential if you wish to put the definition of `yylex' in a separate source file, because `yylex' needs to be able to refer to token type codes and the variable `yylval'. *Note Token Values::. `-l' `--no-lines' Don't put any `#line' preprocessor commands in the parser file. Ordinarily Bison puts them in the parser file so that the C compiler and debuggers will associate errors with your source file, the grammar file. This option causes them to associate errors with the parser file, treating it an independent source file in its own right. `-o OUTFILE' `--output-file=OUTFILE' Specify the name OUTFILE for the parser file. The other output files' names are constructed from OUTFILE as described under the `-v' and `-d' switches. `-p PREFIX' `--name-prefix=PREFIX' Rename the external symbols used in the parser so that they start with PREFIX instead of `yy'. The precise list of symbols renamed is `yyparse', `yylex', `yyerror', `yylval', `yychar' and `yydebug'. For example, if you use `-p c', the names become `cparse', `clex', and so on. *Note Multiple Parsers::. `-t' `--debug' Output a definition of the macro `YYDEBUG' into the parser file, so that the debugging facilities are compiled. *Note Debugging::. `-v' `--verbose' Write an extra output file containing verbose descriptions of the parser states and what is done for each type of look-ahead token in that state. This file also describes all the conflicts, both those resolved by operator precedence and the unresolved ones. The file's name is made by removing `.tab.c' or `.c' from the parser output file name, and adding `.output' instead. Therefore, if the input file is `foo.y', then the parser file is called `foo.tab.c' by default. As a consequence, the verbose output file is called `foo.output'. `-V' `--version' Print the version number of Bison. `-y' `--yacc' `--fixed-output-files' Equivalent to `-o y.tab.c'; the parser output file is called `y.tab.c', and the other outputs are called `y.output' and `y.tab.h'. The purpose of this switch is to imitate Yacc's output file name conventions. Thus, the following shell script can substitute for Yacc: bison -y $* Options' Cross Key ================== Here is a list of options, alphabetized by long option, to help you find the corresponding short option. --debug -t --defines -d --file-prefix=PREFIX -b FILE-PREFIX --fixed-output-files --yacc -y --name-prefix -p --no-lines -l --output-file=OUTFILE -o OUTFILE --verbose -v --version -V File: bison.info, Node: Table of Symbols, Next: Glossary, Prev: Invocation, Up: Top Bison Symbols ************* `error' A token name reserved for error recovery. This token may be used in grammar rules so as to allow the Bison parser to recognize an error in the grammar without halting the process. In effect, a sentence containing an error may be recognized as valid. On a parse error, the token `error' becomes the current look-ahead token. Actions corresponding to `error' are then executed, and the look-ahead token is reset to the token that originally caused the violation. *Note Error Recovery::. `YYABORT' Macro to pretend that an unrecoverable syntax error has occurred, by making `yyparse' return 1 immediately. The error reporting function `yyerror' is not called. *Note Parser Function::. `YYACCEPT' Macro to pretend that a complete utterance of the language has been read, by making `yyparse' return 0 immediately. *Note Parser Function::. `YYBACKUP' Macro to discard a value from the parser stack and fake a look-ahead token. *Note Action Features::. `YYERROR' Macro to pretend that a syntax error has just been detected: call `yyerror' and then perform normal error recovery if possible (*note Error Recovery::.), or (if recovery is impossible) make `yyparse' return 1. *Note Error Recovery::. `YYINITDEPTH' Macro for specifying the initial size of the parser stack. *Note Stack Overflow::. `YYLTYPE' Macro for the data type of `yylloc'; a structure with four members. *Note Token Positions::. `YYMAXDEPTH' Macro for specifying the maximum size of the parser stack. *Note Stack Overflow::. `YYRECOVERING' Macro whose value indicates whether the parser is recovering from a syntax error. *Note Action Features::. `YYSTYPE' Macro for the data type of semantic values; `int' by default. *Note Value Type::. `yychar' External integer variable that contains the integer value of the current look-ahead token. (In a pure parser, it is a local variable within `yyparse'.) Error-recovery rule actions may examine this variable. *Note Action Features::. `yyclearin' Macro used in error-recovery rule actions. It clears the previous look-ahead token. *Note Error Recovery::. `yydebug' External integer variable set to zero by default. If `yydebug' is given a nonzero value, the parser will output information on input symbols and parser action. *Note Debugging::. `yyerrok' Macro to cause parser to recover immediately to its normal mode after a parse error. *Note Error Recovery::. `yyerror' User-supplied function to be called by `yyparse' on error. The function receives one argument, a pointer to a character string containing an error message. *Note Error Reporting::. `yylex' User-supplied lexical analyzer function, called with no arguments to get the next token. *Note Lexical::. `yylval' External variable in which `yylex' should place the semantic value associated with a token. (In a pure parser, it is a local variable within `yyparse', and its address is passed to `yylex'.) *Note Token Values::. `yylloc' External variable in which `yylex' should place the line and column numbers associated with a token. (In a pure parser, it is a local variable within `yyparse', and its address is passed to `yylex'.) You can ignore this variable if you don't use the `@' feature in the grammar actions. *Note Token Positions::. `yynerrs' Global variable which Bison increments each time there is a parse error. (In a pure parser, it is a local variable within `yyparse'.) *Note Error Reporting::. `yyparse' The parser function produced by Bison; call this function to start parsing. *Note Parser Function::. `%left' Bison declaration to assign left associativity to token(s). *Note Precedence Decl::. `%nonassoc' Bison declaration to assign nonassociativity to token(s). *Note Precedence Decl::. `%prec' Bison declaration to assign a precedence to a specific rule. *Note Contextual Precedence::. `%pure_parser' Bison declaration to request a pure (reentrant) parser. *Note Pure Decl::. `%right' Bison declaration to assign right associativity to token(s). *Note Precedence Decl::. `%start' Bison declaration to specify the start symbol. *Note Start Decl::. `%token' Bison declaration to declare token(s) without specifying precedence. *Note Token Decl::. `%type' Bison declaration to declare nonterminals. *Note Type Decl::. `%union' Bison declaration to specify several possible data types for semantic values. *Note Union Decl::. These are the punctuation and delimiters used in Bison input: `%%' Delimiter used to separate the grammar rule section from the Bison declarations section or the additional C code section. *Note Grammar Layout::. `%{ %}' All code listed between `%{' and `%}' is copied directly to the output file uninterpreted. Such code forms the "C declarations" section of the input file. *Note Grammar Outline::. `/*...*/' Comment delimiters, as in C. `:' Separates a rule's result from its components. *Note Rules::. `;' Terminates a rule. *Note Rules::. `|' Separates alternate rules for the same result nonterminal. *Note Rules::. File: bison.info, Node: Glossary, Next: Index, Prev: Table of Symbols, Up: top Glossary ******** Backus-Naur Form (BNF) Formal method of specifying context-free grammars. BNF was first used in the `ALGOL-60' report, 1963. *Note Language and Grammar::. Context-free grammars Grammars specified as rules that can be applied regardless of context. Thus, if there is a rule which says that an integer can be used as an expression, integers are allowed *anywhere* an expression is permitted. *Note Language and Grammar::. Dynamic allocation Allocation of memory that occurs during execution, rather than at compile time or on entry to a function. Empty string Analogous to the empty set in set theory, the empty string is a character string of length zero. Finite-state stack machine A "machine" that has discrete states in which it is said to exist at each instant in time. As input to the machine is processed, the machine moves from state to state as specified by the logic of the machine. In the case of the parser, the input is the language being parsed, and the states correspond to various stages in the grammar rules. *Note Algorithm::. Grouping A language construct that is (in general) grammatically divisible; for example, `expression' or `declaration' in C. *Note Language and Grammar::. Infix operator An arithmetic operator that is placed between the operands on which it performs some operation. Input stream A continuous flow of data between devices or programs. Language construct One of the typical usage schemas of the language. For example, one of the constructs of the C language is the `if' statement. *Note Language and Grammar::. Left associativity Operators having left associativity are analyzed from left to right: `a+b+c' first computes `a+b' and then combines with `c'. *Note Precedence::. Left recursion A rule whose result symbol is also its first component symbol; for example, `expseq1 : expseq1 ',' exp;'. *Note Recursion::. Left-to-right parsing Parsing a sentence of a language by analyzing it token by token from left to right. *Note Algorithm::. Lexical analyzer (scanner) A function that reads an input stream and returns tokens one by one. *Note Lexical::. Lexical tie-in A flag, set by actions in the grammar rules, which alters the way tokens are parsed. *Note Lexical Tie-ins::. Look-ahead token A token already read but not yet shifted. *Note Look-Ahead::. LALR(1) The class of context-free grammars that Bison (like most other parser generators) can handle; a subset of LR(1). *Note Mysterious Reduce/Reduce Conflicts: Mystery Conflicts. LR(1) The class of context-free grammars in which at most one token of look-ahead is needed to disambiguate the parsing of any piece of input. Nonterminal symbol A grammar symbol standing for a grammatical construct that can be expressed through rules in terms of smaller constructs; in other words, a construct that is not a token. *Note Symbols::. Parse error An error encountered during parsing of an input stream due to invalid syntax. *Note Error Recovery::. Parser A function that recognizes valid sentences of a language by analyzing the syntax structure of a set of tokens passed to it from a lexical analyzer. Postfix operator An arithmetic operator that is placed after the operands upon which it performs some operation. Reduction Replacing a string of nonterminals and/or terminals with a single nonterminal, according to a grammar rule. *Note Algorithm::. Reentrant A reentrant subprogram is a subprogram which can be in invoked any number of times in parallel, without interference between the various invocations. *Note Pure Decl::. Reverse polish notation A language in which all operators are postfix operators. Right recursion A rule whose result symbol is also its last component symbol; for example, `expseq1: exp ',' expseq1;'. *Note Recursion::. Semantics In computer languages, the semantics are specified by the actions taken for each instance of the language, i.e., the meaning of each statement. *Note Semantics::. Shift A parser is said to shift when it makes the choice of analyzing further input from the stream rather than reducing immediately some already-recognized rule. *Note Algorithm::. Single-character literal A single character that is recognized and interpreted as is. *Note Grammar in Bison::. Start symbol The nonterminal symbol that stands for a complete valid utterance in the language being parsed. The start symbol is usually listed as the first nonterminal symbol in a language specification. *Note Start Decl::. Symbol table A data structure where symbol names and associated data are stored during parsing to allow for recognition and use of existing information in repeated uses of a symbol. *Note Multi-function Calc::. Token A basic, grammatically indivisible unit of a language. The symbol that describes a token in the grammar is a terminal symbol. The input of the Bison parser is a stream of tokens which comes from the lexical analyzer. *Note Symbols::. Terminal symbol A grammar symbol that has no rules in the grammar and therefore is grammatically indivisible. The piece of text it represents is a token. *Note Language and Grammar::. File: bison.info, Node: Index, Prev: Glossary, Up: top Index ***** * Menu: * $$: Actions. * $N: Actions. * %expect: Expect Decl. * %left: Using Precedence. * %nonassoc: Using Precedence. * %prec: Contextual Precedence. * %pure_parser: Pure Decl. * %right: Using Precedence. * %start: Start Decl. * %token: Token Decl. * %type: Type Decl. * %union: Union Decl. * @N: Action Features. * calc: Infix Calc. * else, dangling: Shift/Reduce. * mfcalc: Multi-function Calc. * rpcalc: RPN Calc. * BNF: Language and Grammar. * Backus-Naur form: Language and Grammar. * Bison declaration summary: Decl Summary. * Bison declarations: Declarations. * Bison declarations (introduction): Bison Declarations. * Bison grammar: Grammar in Bison. * Bison invocation: Invocation. * Bison parser: Bison Parser. * Bison parser algorithm: Algorithm. * Bison symbols, table of: Table of Symbols. * Bison utility: Bison Parser. * C code, section for additional: C Code. * C declarations section: C Declarations. * C-language interface: Interface. * LALR(1): Mystery Conflicts. * LR(1): Mystery Conflicts. * YYABORT: Parser Function. * YYACCEPT: Parser Function. * YYBACKUP: Action Features. * YYDEBUG: Debugging. * YYEMPTY: Action Features. * YYERROR: Action Features. * YYINITDEPTH: Stack Overflow. * YYLTYPE: Token Positions. * YYMAXDEPTH: Stack Overflow. * YYPRINT: Debugging. * YYRECOVERING: Error Recovery. * action: Actions. * action data types: Action Types. * action features summary: Action Features. * actions in mid-rule: Mid-Rule Actions. * actions, semantic: Semantic Actions. * additional C code section: C Code. * algorithm of parser: Algorithm. * associativity: Why Precedence. * calculator, infix notation: Infix Calc. * calculator, multi-function: Multi-function Calc. * calculator, simple: RPN Calc. * character token: Symbols. * compiling the parser: Rpcalc Compile. * conflicts: Shift/Reduce. * conflicts, reduce/reduce: Reduce/Reduce. * conflicts, suppressing warnings of: Expect Decl. * context-dependent precedence: Contextual Precedence. * context-free grammar: Language and Grammar. * controlling function: Rpcalc Main. * dangling else: Shift/Reduce. * data types in actions: Action Types. * data types of semantic values: Value Type. * debugging: Debugging. * declaration summary: Decl Summary. * declarations, Bison: Declarations. * declarations, Bison (introduction): Bison Declarations. * declarations, C: C Declarations. * declaring operator precedence: Precedence Decl. * declaring the start symbol: Start Decl. * declaring token type names: Token Decl. * declaring value types: Union Decl. * declaring value types, nonterminals: Type Decl. * defining language semantics: Semantics. * error: Error Recovery. * error recovery: Error Recovery. * error recovery, simple: Simple Error Recovery. * error reporting function: Error Reporting. * error reporting routine: Rpcalc Error. * examples, simple: Examples. * exercises: Exercises. * file format: Grammar Layout. * finite-state machine: Parser States. * formal grammar: Grammar in Bison. * format of grammar file: Grammar Layout. * glossary: Glossary. * grammar file: Grammar Layout. * grammar rule syntax: Rules. * grammar rules section: Grammar Rules. * grammar, Bison: Grammar in Bison. * grammar, context-free: Language and Grammar. * grouping, syntactic: Language and Grammar. * infix notation calculator: Infix Calc. * interface: Interface. * introduction: Introduction. * invoking Bison: Invocation. * language semantics, defining: Semantics. * layout of Bison grammar: Grammar Layout. * left recursion: Recursion. * lexical analyzer: Lexical. * lexical analyzer, purpose: Bison Parser. * lexical analyzer, writing: Rpcalc Lexer. * lexical tie-in: Lexical Tie-ins. * literal token: Symbols. * look-ahead token: Look-Ahead. * main function in simple example: Rpcalc Main. * mid-rule actions: Mid-Rule Actions. * multi-function calculator: Multi-function Calc. * mutual recursion: Recursion. * nonterminal symbol: Symbols. * operator precedence: Precedence. * operator precedence, declaring: Precedence Decl. * options for invoking Bison: Invocation. * overflow of parser stack: Stack Overflow. * parse error: Error Reporting. * parser: Bison Parser. * parser stack: Algorithm. * parser stack overflow: Stack Overflow. * parser state: Parser States. * polish notation calculator: RPN Calc. * precedence declarations: Precedence Decl. * precedence of operators: Precedence. * precedence, context-dependent: Contextual Precedence. * precedence, unary operator: Contextual Precedence. * preventing warnings about conflicts: Expect Decl. * pure parser: Pure Decl. * recovery from errors: Error Recovery. * recursive rule: Recursion. * reduce/reduce conflict: Reduce/Reduce. * reduction: Algorithm. * reentrant parser: Pure Decl. * reverse polish notation: RPN Calc. * right recursion: Recursion. * rule syntax: Rules. * rules section for grammar: Grammar Rules. * running Bison (introduction): Rpcalc Gen. * semantic actions: Semantic Actions. * semantic value: Semantic Values. * semantic value type: Value Type. * shift/reduce conflicts: Shift/Reduce. * shifting: Algorithm. * simple examples: Examples. * single-character literal: Symbols. * stack overflow: Stack Overflow. * stack, parser: Algorithm. * stages in using Bison: Stages. * start symbol: Language and Grammar. * start symbol, declaring: Start Decl. * state (of parser): Parser States. * summary, Bison declaration: Decl Summary. * summary, action features: Action Features. * suppressing conflict warnings: Expect Decl. * symbol: Symbols. * symbol table example: Mfcalc Symtab. * symbols (abstract): Language and Grammar. * symbols in Bison, table of: Table of Symbols. * syntactic grouping: Language and Grammar. * syntax error: Error Reporting. * syntax of grammar rules: Rules. * terminal symbol: Symbols. * token: Language and Grammar. * token type: Symbols. * token type names, declaring: Token Decl. * tracing the parser: Debugging. * unary operator precedence: Contextual Precedence. * using Bison: Stages. * value type, semantic: Value Type. * value types, declaring: Union Decl. * value types, nonterminals, declaring: Type Decl. * value, semantic: Semantic Values. * warnings, preventing: Expect Decl. * writing a lexical analyzer: Rpcalc Lexer. * yychar: Look-Ahead. * yyclearin: Error Recovery. * yydebug: Debugging. * yyerrok: Error Recovery. * yyerror: Error Reporting. * yylex: Lexical. * yylloc: Token Positions. * yylval: Token Values. * yynerrs: Error Reporting. * yyparse: Parser Function. * |: Rules.