BYACC(1)

NAME
byacc - an LALR(1) parser generator

SYNOPSIS
byacc [ -CPcdlrtv ] [ -b file_prefix ] [ -p symbol_prefix ] filename

DESCRIPTION
byacc reads the grammar specification in the file filename and generates an LR(1) parser for it. The parsers consist of a set of LALR(1) parsing tables and a driver routine written in the C or Perl programming languages. byacc normally writes the parse tables and the driver routine to the file y.tab.c, using the C programming language.

The following options are available:

    -b file_prefix
        The -b option changes the prefix prepended to the output file names to the string denoted by file_prefix. The default prefix is the character y.

    -C or -c
        Use the C programming language (default).

    -d  The -d option causes the header file y.tab.h to be written (or y.tab.ph, for Perl).

    -l  If the -l option is not specified, byacc will insert The generated code to the user's original code. If the -l option is specified, byacc will not insert the

    -p symbol_prefix
        Change the prefix in symbols in the generated code to the string denoted by symbol_prefix rather than the default of "yy". Only symbols generated by byacc are affected. Symbols in the definition and user subroutine sections are not changed.

        The symbol_prefix can contain upper or lower case letters, digits, or _ (underline or underscore). It must start with either an underline or a letter and must contain at least one lower case letter.

        All lower case letters in the symbol prefix will be converted to upper case letters when defined values or typedefs are generated.

        For example, if '-p ftp_' is specifed on the byacc command line:
        old symbol | new symbol
        YYABORT | FTP_ABORT
        YYACCEPT | FTP_ACCEPT
        YYBYACC | FTP_BYACC
        YYDEBUG | FTP_DEBUG
        YYSTYPE | FTP_STYPE
        yyabort | ftp_abort
        yyerrok | ftp_errok
        yylex | ftp_lex
        yylval | ftp_lval
        yyparse | ftp_parse
        Note: The above list is not complete.

    -P  Use the Perl programming language. The output files have extensions .tab.pl and .tab.ph.

    -r  The -r option causes byacc to produce separate files for code and tables. The code file is named y.code.c, and the tables file is named y.tab.c. In Perl mode, the file name extension is .pl, but the use of this option is not recommended.

    -t  The -t option changes the preprocessor directives generated by byacc so that debugging statements will be incorporated in the compiled code.

    -v  The -v option causes a human-readable description of the generated parser to be written to the file y.output.

If the environment variable TMPDIR is set, the string denoted by TMPDIR will be used as the name of the directory where the temporary files are created.

In C mode, the user's code at the end of the BYACC file is inserted before the yyparse subroutine, but in Perl mode, it is appended to yyparse so it can contain the main program. In Perl mode, there is no library, so the user must supply the yyerror and yylex subroutines and a main program that calls yyparse. For example:

    %%
    ...grammar...
    %%
    sub yyerror { print STDERR "$.: $@\n"; }
    sub yylex { ... }
    exit &yyparse;

FILES
y.code.c
    output parser code in C
y.tab.c
    output parser code and tables in C or, if -r switch specified, output parser tables in C
y.tab.h
    defines for token names and, if %union used in grammar, the union definition for C parsers
y.code.pl
    output parser code in PERL
y.tab.pl
    output parser code and tables in PERL or, if -r switch specified, output parser tables in PERL
y.tab.ph
    PERL assignment statements for token names
y.output
    description of parser states, state transitions, and conflicts
/tmp/byacc.aXXXXXX, /tmp/byacc.tXXXXXX, /tmp/byacc.uXXXXXX
    temporary files
/usr/local/lib/libby.a
    library containing simple versions of main() (calls yyparse() then exits) and yyerror() (prints message to stderr then returns)

SEE ALSO
flex(1), lex(1)

Yacc: Yet Another Compiler-Compiler
Stephen C. Johnson
Originally (?) published as Comp. Sci. Tech. Rep. No. 32. Bell Laboratories, July 1975. Reprinted in many different places.

Introduction to Compiler Construction with UNIX
Axel T. Schreiner and H. George Friedman, Jr.
Prentice Hall, 1985.

lex & yacc, Second Edition
John R. Levine, Tony Mason, and Doug Brown
O'Reilly & Associates, Inc., 1992.
Possibly the best book yet on lex and yacc. (My opinion only. Others may disagree. - Rick Ohnemus)

comp.compilers monthly message and Frequently Asked Questions
Posted monthly in comp.compilers and news.answers USENET newsgroups.

DIAGNOSTICS
If there are rules that are never reduced, the number of such rules is reported on standard error.

If there are any LALR(1) conflicts, the number of conflicts is reported on standard error.

RESTRICTIONS
A symbol prefix specified using the -p switch must contain at least one lower case character. This is to allow a distinction between variables, defined values, and typedefs.

BUGS