Appendix A Bison Symbols

Variable: @$: In an action, the location of the left-hand side of the rule. See section Tracking Locations.

Variable: @n

Symbol: @n

In an action, the location of the n-th symbol of the right-hand side of the rule. See section Tracking Locations.

In a grammar, the Bison-generated nonterminal symbol for a mid-rule action with a semantical value. See section Mid-Rule Action Translation.

Variable: @name
Variable: @[name]: In an action, the location of a symbol addressed by name. See section Tracking Locations.

Symbol: $@n: In a grammar, the Bison-generated nonterminal symbol for a mid-rule action with no semantical value. See section Mid-Rule Action Translation.

Variable: $$: In an action, the semantic value of the left-hand side of the rule. See section Actions.

Variable: $n: In an action, the semantic value of the n-th symbol of the right-hand side of the rule. See section Actions.

Variable: $name
Variable: $[name]: In an action, the semantic value of a symbol addressed by name. See section Actions.

Delimiter: %%: Delimiter used to separate the grammar rule section from the Bison declarations section or the epilogue. See section The Overall Layout of a Bison Grammar.

Delimiter: %{code%}: All code listed between ‘%{’ and ‘%}’ is copied verbatim to the parser implementation file. Such code forms the prologue of the grammar file. See section Outline of a Bison Grammar.

Directive: %?{expression}

Predicate actions. This is a type of action clause that may appear in rules. The expression is evaluated, and if false, causes a syntax error. In GLR parsers during nondeterministic operation, this silently causes an alternative parse to die. During deterministic operation, it is the same as the effect of YYERROR. See section Controlling a Parse with Arbitrary Predicates.

This feature is experimental. More user feedback will help to determine whether it should become a permanent feature.

Construct: /* … */
Construct: // …: Comments, as in C/C++.

Delimiter: :: Separates a rule’s result from its components. See section Syntax of Grammar Rules.

Delimiter: ;: Terminates a rule. See section Syntax of Grammar Rules.

Delimiter: |: Separates alternate rules for the same result nonterminal. See section Syntax of Grammar Rules.

Directive: <*>

Used to define a default tagged %destructor or default tagged %printer.

This feature is experimental. More user feedback will help to determine whether it should become a permanent feature.

See section Freeing Discarded Symbols.

Directive: <>

Used to define a default tagless %destructor or default tagless %printer.

This feature is experimental. More user feedback will help to determine whether it should become a permanent feature.

See section Freeing Discarded Symbols.

Symbol: $accept: The predefined nonterminal whose only rule is ‘$accept: start $end’, where start is the start symbol. See section The Start-Symbol. It cannot be used in the grammar.

Directive: %code {code}
Directive: %code qualifier {code}: Insert code verbatim into the output parser source at the default location or at the location specified by qualifier. See section %code Summary.

Directive: %debug: Equip the parser for debugging. See section Bison Declaration Summary.

Directive: %define variable
Directive: %define variable value
Directive: %define variable {value}
Directive: %define variable "value": Define a variable to adjust Bison’s behavior. See section %define Summary.

Directive: %defines: Bison declaration to create a parser header file, which is usually meant for the scanner. See section Bison Declaration Summary.

Directive: %defines defines-file: Same as above, but save in the file defines-file. See section Bison Declaration Summary.

Directive: %destructor: Specify how the parser should reclaim the memory associated to discarded symbols. See section Freeing Discarded Symbols.

Directive: %dprec: Bison declaration to assign a precedence to a rule that is used at parse time to resolve reduce/reduce conflicts. See section Writing GLR Parsers.

Directive: %empty: Bison declaration to declare make explicit that a rule has an empty right-hand side. See section Empty Rules.

Symbol: $end: The predefined token marking the end of the token stream. It cannot be used in the grammar.

Symbol: 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 syntax error, the token error becomes the current lookahead token. Actions corresponding to error are then executed, and the lookahead token is reset to the token that originally caused the violation. See section Error Recovery.

Directive: %error-verbose: An obsolete directive standing for ‘%define parse.error verbose’ (see section The Error Reporting Function yyerror).

Directive: %file-prefix "prefix": Bison declaration to set the prefix of the output files. See section Bison Declaration Summary.

Directive: %glr-parser: Bison declaration to produce a GLR parser. See section Writing GLR Parsers.

Directive: %initial-action: Run user code before parsing. See section Performing Actions before Parsing.

Directive: %language: Specify the programming language for the generated parser. See section Bison Declaration Summary.

Directive: %left: Bison declaration to assign precedence and left associativity to token(s). See section Operator Precedence.

Directive: %lex-param {argument-declaration} …: Bison declaration to specifying additional arguments that yylex should accept. See section Calling Conventions for Pure Parsers.

Directive: %merge: Bison declaration to assign a merging function to a rule. If there is a reduce/reduce conflict with a rule having the same merging function, the function is applied to the two semantic values to get a single result. See section Writing GLR Parsers.

Directive: %name-prefix "prefix"

Obsoleted by the %define variable api.prefix (see section Multiple Parsers in the Same Program).

Rename the external symbols (variables and functions) used in the parser so that they start with prefix instead of ‘yy’. Contrary to api.prefix, do no rename types and macros.

The precise list of symbols renamed in C parsers is yyparse, yylex, yyerror, yynerrs, yylval, yychar, yydebug, and (if locations are used) yylloc. If you use a push parser, yypush_parse, yypull_parse, yypstate, yypstate_new and yypstate_delete will also be renamed. For example, if you use ‘%name-prefix "c_"’, the names become c_parse, c_lex, and so on. For C++ parsers, see the %define api.namespace documentation in this section.

Directive: %no-lines: Bison declaration to avoid generating #line directives in the parser implementation file. See section Bison Declaration Summary.

Directive: %nonassoc: Bison declaration to assign precedence and nonassociativity to token(s). See section Operator Precedence.

Directive: %output "file": Bison declaration to set the name of the parser implementation file. See section Bison Declaration Summary.

Directive: %param {argument-declaration} …: Bison declaration to specify additional arguments that both yylex and yyparse should accept. See section The Parser Function yyparse.

Directive: %parse-param {argument-declaration} …: Bison declaration to specify additional arguments that yyparse should accept. See section The Parser Function yyparse.

Directive: %prec: Bison declaration to assign a precedence to a specific rule. See section Context-Dependent Precedence.

Directive: %precedence: Bison declaration to assign precedence to token(s), but no associativity See section Operator Precedence.

Directive: %pure-parser: Deprecated version of ‘%define api.pure’ (see section api.pure), for which Bison is more careful to warn about unreasonable usage.

Directive: %require "version": Require version version or higher of Bison. See section Require a Version of Bison.

Directive: %right: Bison declaration to assign precedence and right associativity to token(s). See section Operator Precedence.

Directive: %skeleton: Specify the skeleton to use; usually for development. See section Bison Declaration Summary.

Directive: %start: Bison declaration to specify the start symbol. See section The Start-Symbol.

Directive: %token: Bison declaration to declare token(s) without specifying precedence. See section Token Type Names.

Directive: %token-table: Bison declaration to include a token name table in the parser implementation file. See section Bison Declaration Summary.

Directive: %type: Bison declaration to declare nonterminals. See section Nonterminal Symbols.

Symbol: $undefined: The predefined token onto which all undefined values returned by yylex are mapped. It cannot be used in the grammar, rather, use error.

Directive: %union: Bison declaration to specify several possible data types for semantic values. See section The Union Declaration.

Macro: 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. See section The Parser Function yyparse.

For Java parsers, this functionality is invoked using return YYABORT; instead.

Macro: YYACCEPT

Macro to pretend that a complete utterance of the language has been read, by making yyparse return 0 immediately. See section The Parser Function yyparse.

For Java parsers, this functionality is invoked using return YYACCEPT; instead.

Macro: YYBACKUP: Macro to discard a value from the parser stack and fake a lookahead token. See section Special Features for Use in Actions.

Variable: yychar: External integer variable that contains the integer value of the lookahead token. (In a pure parser, it is a local variable within yyparse.) Error-recovery rule actions may examine this variable. See section Special Features for Use in Actions.

Variable: yyclearin: Macro used in error-recovery rule actions. It clears the previous lookahead token. See section Error Recovery.

Macro: YYDEBUG: Macro to define to equip the parser with tracing code. See section Tracing Your Parser.

Variable: 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. See section Tracing Your Parser.

Macro: yyerrok: Macro to cause parser to recover immediately to its normal mode after a syntax error. See section Error Recovery.

Macro: YYERROR

Cause an immediate syntax error. This statement initiates error recovery just as if the parser itself had detected an error; however, it does not call yyerror, and does not print any message. If you want to print an error message, call yyerror explicitly before the ‘YYERROR;’ statement. See section Error Recovery.

For Java parsers, this functionality is invoked using return YYERROR; instead.

Function: yyerror: User-supplied function to be called by yyparse on error. See section The Error Reporting Function yyerror.

Macro: YYERROR_VERBOSE: An obsolete macro used in the ‘yacc.c’ skeleton, that you define with #define in the prologue to request verbose, specific error message strings when yyerror is called. It doesn’t matter what definition you use for YYERROR_VERBOSE, just whether you define it. Using ‘%define parse.error verbose’ is preferred (see section The Error Reporting Function yyerror).

Macro: YYFPRINTF: Macro used to output run-time traces. See section Enabling Traces.

Macro: YYINITDEPTH: Macro for specifying the initial size of the parser stack. See section Memory Management, and How to Avoid Memory Exhaustion.

Function: yylex: User-supplied lexical analyzer function, called with no arguments to get the next token. See section The Lexical Analyzer Function yylex.

Variable: 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. See section Textual Locations of Tokens. In semantic actions, it stores the location of the lookahead token. See section Actions and Locations.

Type: YYLTYPE: Data type of yylloc; by default, a structure with four members. See section Data Types of Locations.

Variable: 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.) See section Semantic Values of Tokens. In semantic actions, it stores the semantic value of the lookahead token. See section Actions.

Macro: YYMAXDEPTH: Macro for specifying the maximum size of the parser stack. See section Memory Management, and How to Avoid Memory Exhaustion.

Variable: yynerrs: Global variable which Bison increments each time it reports a syntax error. (In a pure parser, it is a local variable within yyparse. In a pure push parser, it is a member of yypstate.) See section The Error Reporting Function yyerror.

Function: yyparse: The parser function produced by Bison; call this function to start parsing. See section The Parser Function yyparse.

Macro: YYPRINT: Macro used to output token semantic values. For ‘yacc.c’ only. Obsoleted by %printer. See section The YYPRINT Macro.

Function: yypstate_delete: The function to delete a parser instance, produced by Bison in push mode; call this function to delete the memory associated with a parser. See section The Parser Delete Function yypstate_delete. (The current push parsing interface is experimental and may evolve. More user feedback will help to stabilize it.)

Function: yypstate_new: The function to create a parser instance, produced by Bison in push mode; call this function to create a new parser. See section The Parser Create Function yypstate_new. (The current push parsing interface is experimental and may evolve. More user feedback will help to stabilize it.)

Function: yypull_parse: The parser function produced by Bison in push mode; call this function to parse the rest of the input stream. See section The Pull Parser Function yypull_parse. (The current push parsing interface is experimental and may evolve. More user feedback will help to stabilize it.)

Function: yypush_parse: The parser function produced by Bison in push mode; call this function to parse a single token. See section The Push Parser Function yypush_parse. (The current push parsing interface is experimental and may evolve. More user feedback will help to stabilize it.)

Macro: YYRECOVERING: The expression YYRECOVERING () yields 1 when the parser is recovering from a syntax error, and 0 otherwise. See section Special Features for Use in Actions.

Macro: YYSTACK_USE_ALLOCA

Macro used to control the use of alloca when the deterministic parser in C needs to extend its stacks. If defined to 0, the parser will use malloc to extend its stacks. If defined to 1, the parser will use alloca. Values other than 0 and 1 are reserved for future Bison extensions. If not defined, YYSTACK_USE_ALLOCA defaults to 0.

In the all-too-common case where your code may run on a host with a limited stack and with unreliable stack-overflow checking, you should set YYMAXDEPTH to a value that cannot possibly result in unchecked stack overflow on any of your target hosts when alloca is called. You can inspect the code that Bison generates in order to determine the proper numeric values. This will require some expertise in low-level implementation details.

Type: YYSTYPE: Deprecated in favor of the %define variable api.value.type. Data type of semantic values; int by default. See section Data Types of Semantic Values.

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