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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 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:

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

		    |	 STAT CRLF
			 = {
			      statcmd();
			 }

       o   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.

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

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

       o   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)
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