| YACC(1) | General Commands Manual | YACC(1) | 
yacc —
| yacc | [ -BdgilLPrtvVy] [-bfile_prefix] [-ooutput_file] [-psymbol_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
  y.tab.c.
The following options are available:
-b
    file_prefix-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.-Byacc).-d-d option causes the header file
      y.tab.h to be written. It contains #define's for
      the token identifiers.-g-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-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-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.-Lyacc).-o
    output_file-b option.-P-P options instructs
      yacc to create a reentrant parser, like
      “%pure-parser” does.-p
    symbol_prefix-p option changes the prefix prepended to
      yacc-generated symbols to the string denoted by
      symbol_prefix. The default prefix is the string
      yy.-r-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.-syacc 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
    
    yacc does not generate the second
      “#define”. The -s option suppresses
      this “#define”.
    IEEE Std 1003.1
        (“POSIX.1”) documents only names and numbers for
        “%token”, though the original yacc
        and bison(1) also accept
        string literals.
-t-t option changes the preprocessor directives
      generated by yacc so that debugging statements
      will be incorporated in the compiled code.-V-V option prints the version number to the
      standard output.-v-v option causes a human-readable description
      of the generated parser to be written to the file
      y.output.-yyacc ignores this option, which
      bison(1) supports for
      ostensible POSIX compatibility.yacc provides some extensions for compatibility with
  bison(1) 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 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 “@$”
    designates its location (see “%locations” directive).
A per-symbol destructor is defined by listing a grammar symbol in
    symbol+. A per-type destructor is defined by listing
    a semantic type tag (e.g., “<some_tag>”) in
    symbol+; in this case, the parser will invoke
    code whenever it discards any grammar symbol that
    has that semantic type tag, unless that symbol has its own per-symbol
    destructor.
Two categories of default destructor are supported that are invoked when discarding any grammar symbol that has no per-symbol and no per-type destructor:
The code for “<*>” is used for grammar symbols that have an explicitly declared semantic type tag (via “%type”);
the code for “<>” is used for grammar symbols that have no declared semantic type tag.
%expect
    numberyacc the expected number of shift/reduce
      conflicts. That makes it only report the number if it differs.%expect-rr
    numberyacc the expected number of reduce/reduce
      conflicts. That makes it only report the number if it differs. This is
      (unlike bison(1)) allowable
      in LALR(1) parsers.%locationsyacc to enable management of position
      information associated with each token, provided by the lexer in the
      global variable yylloc, similar to management of
      semantic value information provided in yylval.
    As for semantic values, locations can be referenced within
        actions using @$ 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(1), 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
    }yylex(). Use this directive to add parameter
      declarations for your customized lexer.%parse-param
    { argument-declaration
    }yyparse(). Use this directive to add parameter
      declarations for your customized parser.%pure-parseryyparse(), making the parser reasonably
    reentrant.%token-tableyytname array. However,
      yacc yacc does not predefine “$end”,
      “$error” or “$undefined” in this array.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(1). 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(1) emit code in different
  order, and in particular bison(1)
  makes forward reference to common functions such as
  yylex(), yyparse() and
  yyerror() without providing prototypes.
bison(1) support for “%expect” is broken in more than one release. For best results using bison(1), delete that directive.
bison(1) no
    equivalent for some of 's command-line options,
    relying on directives embedded in the grammar file.
bison(1)
    -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(1) accepts the latter (though undocumented), but depending on the release may generate bad code.
Like bison(1),
    yacc will add parameters specified via
    “%parse-param” to yyparse(),
    yyerror() and (if configured for back-tracking) to
    the destructor declared using “%destructor”.
bison(1) puts the
    additional parameters first for
    yyparse() and yyerror() but
    last for destructors. yacc
    matches this behavior.
yacc:
TMPDIRTMPDIR is set, the
      string denoted by TMPDIR will be used as the name
      of the directory where the temporary files are created.yacc are “yylhs”, “yylen”,
  “yydefred”, “yydgoto”, “yysindex”,
  “yyrindex”, “yygindex”, “yytable”,
  and “yycheck”. Two additional tables, “yyname” and
  “yyrule”, are created if YYDEBUG is
  defined and non-zero.
yacc utility conforms to IEEE Std
  1003.2 (“POSIX.2”).
| October 5, 2014 | NetBSD 9.4 |