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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 lan-
       guage.  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  consistent usage of the symbols defined in those
	    files.

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

       -l   If	the  -l	option is not specified, yacc will insert #line	direc-
	    tives in the generated code.  The #line directives let the C  com-
	    piler  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  sym-
	    bols  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 gen-
	    erates 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 original yacc and bison also accept string	liter-
	    als.

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

       -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 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  cus-
	      tomized parser.

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

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 directives 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  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)

NAME | SYNOPSIS | DESCRIPTION | EXTENSIONS | PORTABILITY | DIAGNOSTICS

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