Provided by: byacc_2.0.20220114-1_amd64 bug


       byacc - an LALR(1) parser generator


       yacc  [  -BdghilLPrtvVy  ]  [ -b file_prefix ] [ -H defines_file ] [ -o output_file ] [ -p
       symbol_prefix ] filename


       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

       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-time configuration for btyacc).

       -d   causes the header file to be written.  It contains #define's  for  the  token

       -h   print a usage message.

       -H defines_file
            causes  #define's  for  the token identifiers to be written to the given defines_file
            rather than the file used by the -d option.

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

       -i   The  -i option causes a supplementary header file 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.,
   is modified to #include this file as well  as  the  file,  enforcing
            consistent usage of the symbols defined in those files.

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

       -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-time  configuration  for

       -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.,  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  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.

       The  filename  parameter  is not optional.  However, yacc accepts a single “-” to read the
       grammar from the standard input.  A double “--” marker denotes  the  end  of  options.   A
       single filename parameter is expected after a “--” marker.


       Yacc  provides  some  extensions for compatibility with bison and other implementations of
       yacc.  It accepts several long options which have equivalents in  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

        %code keyword { code }
              Adds  the  indicated source code at a given point in the output file.  The optional
              keyword tells yacc where to insert the code:

              top  just after the version-definition in the generated code-file.

                   just after the declaration of public parser variables.  If the  -d  option  is
                   given, the code is inserted at the beginning of the defines-file.

                   just  after  the declaration of private parser variables.  If the -d option is
                   given, the code is inserted at the end of the defines-file.

              If no keyword is given, the code is inserted at the beginning  of  the  section  of
              code copied verbatim from the source file.  Multiple %code directives may be given;
              yacc inserts those into the corresponding code- or defines-file in the  order  that
              they appear in the source file.

        %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

              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.

              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.

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

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


       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


       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
                      = {

       •   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

       •   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 command-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.

       •   Yacc accepts multiple parameters with %lex-param and %parse-param in two forms

              {type1 name1} {type2 name2} ...
              {type1 name1,  type2 name2 ...}

           Bison  accepts  the  latter  (though  undocumented),  but depending on the release may
           generate bad code.

       •   Like bison, yacc will add parameters specified via %parse-param  to  yyparse,  yyerror
           and  (if  configured  for back-tracking) to the destructor declared using %destructor.
           Bison puts the additional parameters first  for  yyparse  and  yyerror  but  last  for
           destructors.  Yacc matches this behavior.


       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.