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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 written 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  identi‐
            fiers.

       -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 consistent 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_pre‐
            fix.  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,

       -v   The  -v  option  causes  a  human-readable  description of the generated parser to be written 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 decla‐
              rations 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
                         = {

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



Berkeley Yacc                                     September 7, 2011                                           YACC(1)