info bison

3.7.11 Bison Declaration Summary

Here is a summary of the declarations used to define a grammar:

Directive: %union: Declare the collection of data types that semantic values may have (see section The Collection of Value Types).

Directive: %token: Declare a terminal symbol (token type name) with no precedence or associativity specified (see section Token Type Names).

Directive: %right: Declare a terminal symbol (token type name) that is right-associative (see section Operator Precedence).

Directive: %left: Declare a terminal symbol (token type name) that is left-associative (see section Operator Precedence).

Directive: %nonassoc: Declare a terminal symbol (token type name) that is nonassociative (see section Operator Precedence). Using it in a way that would be associative is a syntax error.

Directive: %type: Declare the type of semantic values for a nonterminal symbol (see section Nonterminal Symbols).

Directive: %start: Specify the grammar's start symbol (see section The Start-Symbol).

Directive: %expect: Declare the expected number of shift-reduce conflicts (see section Suppressing Conflict Warnings).

In order to change the behavior of bison, use the following directives:

Directive: %debug: In the parser file, define the macro YYDEBUG to 1 if it is not already defined, so that the debugging facilities are compiled.

See section Tracing Your Parser.

Directive: %defines

Write a header file containing macro definitions for the token type names defined in the grammar as well as a few other declarations. If the parser output file is named ‘name.c’ then this file is named ‘name.h’.

Unless YYSTYPE is already defined as a macro, the output header declares YYSTYPE. Therefore, if you are using a %union (see section More Than One Value Type) with components that require other definitions, or if you have defined a YYSTYPE macro (see section Data Types of Semantic Values), you need to arrange for these definitions to be propagated to all modules, e.g., by putting them in a prerequisite header that is included both by your parser and by any other module that needs YYSTYPE.

Unless your parser is pure, the output header declares yylval as an external variable. See section A Pure (Reentrant) Parser.

If you have also used locations, the output header declares YYLTYPE and yylloc using a protocol similar to that of YYSTYPE and yylval. See section Tracking Locations.

This output file is normally essential if you wish to put the definition of yylex in a separate source file, because yylex typically needs to be able to refer to the above-mentioned declarations and to the token type codes. See section Semantic Values of Tokens.

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

Directive: %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.y’.

Directive: %locations: Generate the code processing the locations (see section Special Features for Use in Actions). This mode is enabled as soon as the grammar uses the special ‘@n’ tokens, but if your grammar does not use it, using ‘%locations’ allows for more accurate syntax error messages.

Directive: %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 in C parsers is yyparse, yylex, yyerror, yynerrs, yylval, yychar, yydebug, and (if locations are used) yylloc. For example, if you use ‘%name-prefix="c_"’, the names become c_parse, c_lex, and so on. In C++ parsers, it is only the surrounding namespace which is named prefix instead of ‘yy’. See section Multiple Parsers in the Same Program.

Directive: %no-parser

Do not include any C code in the parser file; generate tables only. The parser file contains just #define directives and static variable declarations.

This option also tells Bison to write the C code for the grammar actions into a file named ‘file.act’, in the form of a brace-surrounded body fit for a switch statement.

Directive: %no-lines: Don't generate any #line preprocessor commands in the parser file. Ordinarily Bison writes these commands in the parser file so that the C compiler and debuggers will associate errors and object code with your source file (the grammar file). This directive causes them to associate errors with the parser file, treating it an independent source file in its own right.

Directive: %output="file": Specify file for the parser file.

Directive: %pure-parser: Request a pure (reentrant) parser program (see section A Pure (Reentrant) Parser).

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

Directive: %token-table

Generate an array of token names in the parser file. The name of the array is yytname; yytname[i] is the name of the token whose internal Bison token code number is i. The first three elements of yytname correspond to the predefined tokens "$end", "error", and "$undefined"; after these come the symbols defined in the grammar file.

The name in the table includes all the characters needed to represent the token in Bison. For single-character literals and literal strings, this includes the surrounding quoting characters and any escape sequences. For example, the Bison single-character literal '+' corresponds to a three-character name, represented in C as "'+'"; and the Bison two-character literal string "\\/" corresponds to a five-character name, represented in C as "\"\\\\/\"".

When you specify %token-table, Bison also generates macro definitions for macros YYNTOKENS, YYNNTS, and YYNRULES, and YYNSTATES:

YYNTOKENS: The highest token number, plus one.
YYNNTS: The number of nonterminal symbols.
YYNRULES: The number of grammar rules,
YYNSTATES: The number of parser states (see section Parser States).

Directive: %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. See section Understanding Your Parser, for more information.

Directive: %yacc: Pretend the option ‘--yacc’ was given, i.e., imitate Yacc, including its naming conventions. See section Bison Options, for more.

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