Provided by: byacc_20140715-1build1_amd64 bug

NAME

       Yacc - an LALR(1) parser generator

SYNOPSIS

       yacc [ -BdgilLPrtvVy ] [ -b file_prefix ] [ -o output_file ] [ -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.

       -B   create a backtracking parser (compile-type configuration for btyacc).

       -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 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.

       -L   enable  position  processing,  e.g.,  “%locations”  (compile-type  configuration  for
            btyacc).

       -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 -b 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
            original 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
            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.  The %destructor and %locations  features  are  available  only  if  yacc  has  been
       configured  and  compiled  to  support  the  back-tracking  (btyacc)  functionality.   The
       remaining features are always available:

        %destructor { code } symbol+
              defines code that is invoked when a symbol is automatically discarded during  error
              recovery.  This code can be used to reclaim dynamically allocated memory associated
              with the corresponding semantic value for cases where user  actions  cannot  manage
              the memory explicitly.

              On  encountering  a parse error, the generated parser discards symbols on the stack
              and input tokens until it reaches a state that  will  allow  parsing  to  continue.
              This  error  recovery approach results in a memory leak if the YYSTYPE value is, or
              contains, pointers to dynamically allocated memory.

              The bracketed code is invoked whenever the parser  discards  one  of  the  symbols.
              Within  code,  “$$”  or “$<tag>$” designates the semantic value associated with the
              discarded symbol, and  “@$” designates its location (see %locations directive).

              A per-symbol destructor is defined by listing a grammar symbol in symbol+.  A  per-
              type  destructor is defined  by listing a semantic type tag (e.g., “<some_tag>”) in
              symbol+; in this case, the parser will invoke code whenever it discards any grammar
              symbol  that  has that semantic type tag, unless that symbol has its own per-symbol
              destructor.

              Two categories of default destructor are supported that are invoked when discarding
              any grammar symbol that has no per-symbol and no per-type destructor:

              ·   the code for “<*>” is used for grammar symbols that have an explicitly declared
                  semantic type tag (via “%type”);

              ·   the code for “<>” is used for grammar symbols that have  no  declared  semantic
                  type tag.

        %expect number
              tells  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.

        %locations
              tells  yacc  to  enable   management  of  position information associated with each
              token, provided by the lexer in the global variable yylloc, similar  to  management
              of semantic value information provided in yylval.

              As  for  semantic  values,  locations  can be referenced within actions using @$ to
              refer to the location of the left hand side symbol, and @N (N an integer) to  refer
              to the location of one of the right hand side symbols. Also as for semantic values,
              when a rule is  matched,  a  default  action  is  used  the  compute  the  location
              represented  by  @$  as  the  beginning of the first symbol and the end of the last
              symbol in the right hand  side  of  the  rule.  This  default  computation  can  be
              overridden by explicit assignment to @$ in a rule action.

              The type of yylloc is YYLTYPE, which is defined by default as:

                  typedef struct YYLTYPE {
                      int first_line;
                      int first_column;
                      int last_line;
                      int last_column;
                  } YYLTYPE;

              YYLTYPE  can  be  redefined  by  the  user  (YYLTYPE_IS_DEFINED must be defined, to
              inhibit the default) in the declarations section of the specification file.  As  in
              bison, the macro YYLLOC_DEFAULT is invoked each time a rule is matched to calculate
              a position for the left hand side of the rule,  before  the  associated  action  is
              executed; this macro can be redefined by the user.

              This  directive  adds  a  YYLTYPE  parameter  to  yyerror().   If  the %pure-parser
              directive is present, a YYLTYPE parameter is added to yylex() calls.

        %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.

        %token-table
              Make  the  parser's names for tokens available in the yytname array.  However, yacc
              does not predefine “$end”, “$error” or “$undefined” in this array.

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