YACC(1)                                   User Commands                                   YACC(1)



NAME
       Yacc - an LALR(1) parser generator

SYNOPSIS
       yacc [ -dgilrtv ] [ -b file_prefix ] [ -p symbol_prefix ] filename

DESCRIPTION
       Yacc  reads the grammar specification in the file filename and generates an LALR(1) parser
       for it.  The parsers consist of a set of LALR(1) parsing tables and a driver routine writ-
       ten  in  the C programming language.  Yacc normally writes the parse tables and the driver
       routine to the file y.tab.c.

       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.

       -d   The  -d  option  causes the header file y.tab.h to be written.  It contains #define's
            for the token identifiers.

       -g   The -g option causes a graphical description of the generated LALR(1)  parser  to  be
            written to the file y.dot in graphviz format, ready to be processed by dot(1).

       -i   The  -i option causes a supplementary header file y.tab.i to be written.  It contains
            extern declarations and supplementary #define's as needed  to  map  the  conventional
            yacc  yy-prefixed  names to whatever the -p option may specify.  The code file, e.g.,
            y.tab.c is modified to #include this file as well as the y.tab.h file, enforcing con-
            sistent usage of the symbols defined in those files.

            The  supplementary  header  file makes it simpler to separate compilation of lex- and
            yacc-files.

       -l   If the -l option is not specified, yacc will insert #line directives in the generated
            code.  The #line directives let the C compiler relate errors in the generated code to
            the user's original code.  If the -l option is specified, yacc will  not  insert  the
            #line directives.  #line directives specified by the user will be retained.

       -o output_file
            specify  the  filename  for the parser file.  If this option is not given, the output
            filename is the file prefix concatenated with the file suffix, e.g.,  y.tab.c.   This
            overrides the -p option.

       -p symbol_prefix
            The  -p  option  changes the prefix prepended to yacc-generated symbols to the string
            denoted by symbol_prefix.  The default prefix is the string yy.

       -P   create a reentrant parser, e.g., "%pure-parser".

       -r   The -r option causes yacc 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.  The prefix "y." can be
            overridden using the -b option.

       -s   suppress "#define" statements generated for string literals in a "%token"  statement,
            to more closely match original yacc behavior.

            Normally when yacc sees a line such as

                %token OP_ADD "ADD"

            it notices that the quoted "ADD" is a valid C identifier, and generates a #define not
            only for OP_ADD, but for ADD as well, e.g.,

                #define OP_ADD 257
                #define ADD 258

            The original yacc does not generate the second "#define".  The -s  option  suppresses
            this "#define".

            POSIX (IEEE 1003.1 2004) documents only names and numbers for "%token", though origi-
            nal yacc and bison also accept string literals.

       -t   The -t option changes the preprocessor directives generated by yacc 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 writ-
            ten to the file y.output.

       -V   print the version number to the standard output.

       -y   yacc ignores this option, which bison supports for ostensible POSIX compatibility.

EXTENSIONS
       yacc provides some extensions for compatibility with bison and  other  implementations  of
       yacc:

        %expect number
              tell yacc the expected number of shift/reduce conflicts.  That makes it only report
              the number if it differs.

        %expect-rr number
              tell yacc the expected number of  reduce/reduce  conflicts.   That  makes  it  only
              report the number if it differs.  This is (unlike bison) allowable in LALR parsers.

        %lex-param { argument-declaration }
              By  default, the lexer accepts no parameters, e.g., yylex().  Use this directive to
              add parameter declarations for your customized lexer.

        %parse-param { argument-declaration }
              By default, the parser accepts no parameters, e.g., yyparse().  Use this  directive
              to add parameter declarations for your customized parser.

        %pure-parser
              Most  variables  (other than yydebug and yynerrs) are allocated on the stack within
              yyparse, making the parser reasonably reentrant.

PORTABILITY
       According to Robert Corbett,

               Berkeley Yacc is an LALR(1) parser generator.  Berkeley Yacc has been made
           as compatible as possible with AT&T Yacc.  Berkeley Yacc can accept any input
           specification that conforms to the AT&T Yacc documentation.  Specifications
           that take advantage of undocumented features of AT&T Yacc will probably be
           rejected.

       The rationale in

           http://pubs.opengroup.org/onlinepubs/9699919799/utilities/yacc.html

       documents some features of AT&T yacc which are no longer required for POSIX compliance.

       That said, you may be interested in reusing grammary files with some other  implementation
       which  is not strictly compatible with AT&T yacc.  For instance, there is bison.  Here are
       a few differences:

       *   Yacc accepts an equals mark preceding the left curly brace of an  action  (as  in  the
           original grammar file ftp.y):

                    |    STAT CRLF
                         = {
                              statcmd();
                         }

       *   Yacc  and  bison  emit  code in different order, and in particular bison makes forward
           reference to common functions such as yylex, yyparse  and  yyerror  without  providing
           prototypes.

       *   Bison's  support  for  "%expect" is broken in more than one release.  For best results
           using bison, delete that directive.

       *   Bison has no equivalent for some of yacc's commmand-line options,  relying  on  direc-
           tives embedded in the grammar file.

       *   Bison's  "-y" option does not affect bison's lack of support for features of AT&T yacc
           which were deemed obsolescent.

DIAGNOSTICS
       If there are rules that are never reduced, the number of such rules is reported  on  stan-
       dard  error.   If  there are any LALR(1) conflicts, the number of conflicts is reported on
       standard error.



Berkeley Yacc                           September 7, 2011                                 YACC(1)