[ANNOUNCEMENT] Updated: bison-2.4.1-1

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

I've made a new version of 'bison' available for download.  This updates
the package to the latest version available from ftp.gnu.org.  I've included
the relevant portions of the Bison NEWS file at the end of this message.

For a brief description of this package, see http://cygwin.com/packages/ .

To update your installation, click on the "Install Cygwin now" link on
the http://cygwin.com/ web page.  This downloads setup.exe to your
system.  Run setup.exe to install or update the bison package.

If you have questions or comments, please send them to the Cygwin
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Bison News
----------

* Changes in version 2.4.1 (2008-12-11):

** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
   declarations have been fixed.

** Temporary hack for adding a semicolon to the user action.

  Bison used to prepend a trailing semicolon at the end of the user
  action for reductions.  This allowed actions such as

    exp: exp "+" exp { $$ = $1 + $3 };

  instead of

    exp: exp "+" exp { $$ = $1 + $3; };

  Some grammars still depend on this `feature'.  Bison 2.4.1 restores
  the previous behavior in the case of C output (specifically, when
  neither %language or %skeleton or equivalent command-line options
  are used) to leave more time for grammars depending on the old
  behavior to be adjusted.  Future releases of Bison will disable this
  feature.

** A few minor improvements to the Bison manual.

* Changes in version 2.4 (2008-11-02):

** %language is an experimental feature.

  We first introduced this feature in test release 2.3b as a cleaner
  alternative to %skeleton.  Since then, we have discussed the possibility of
  modifying its effect on Bison's output file names.  Thus, in this release,
  we consider %language to be an experimental feature that will likely evolve
  in future releases.

** Forward compatibility with GNU M4 has been improved.

** Several bugs in the C++ skeleton and the experimental Java skeleton have been
  fixed.

* Changes in version 2.3b (2008-05-27):

** The quotes around NAME that used to be required in the following directive
  are now deprecated:

    %define NAME "VALUE"

** The directive `%pure-parser' is now deprecated in favor of:

    %define api.pure

  which has the same effect except that Bison is more careful to warn about
  unreasonable usage in the latter case.

** Push Parsing

  Bison can now generate an LALR(1) parser in C with a push interface.  That
  is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
  push one token at a time to the parser using `yypush_parse', which will
  return to the caller after processing each token.  By default, the push
  interface is disabled.  Either of the following directives will enable it:

    %define api.push_pull "push" // Just push; does not require yylex.
    %define api.push_pull "both" // Push and pull; requires yylex.

  See the new section `A Push Parser' in the Bison manual for details.

  The current push parsing interface is experimental and may evolve.  More user
  feedback will help to stabilize it.

** The -g and --graph options now output graphs in Graphviz DOT format,
  not VCG format.  Like --graph, -g now also takes an optional FILE argument
  and thus cannot be bundled with other short options.

** Java

  Bison can now generate an LALR(1) parser in Java.  The skeleton is
  `data/lalr1.java'.  Consider using the new %language directive instead of
  %skeleton to select it.

  See the new section `Java Parsers' in the Bison manual for details.

  The current Java interface is experimental and may evolve.  More user
  feedback will help to stabilize it.

** %language

  This new directive specifies the programming language of the generated
  parser, which can be C (the default), C++, or Java.  Besides the skeleton
  that Bison uses, the directive affects the names of the generated files if
  the grammar file's name ends in ".y".

** XML Automaton Report

  Bison can now generate an XML report of the LALR(1) automaton using the new
  `--xml' option.  The current XML schema is experimental and may evolve.  More
  user feedback will help to stabilize it.

** The grammar file may now specify the name of the parser header file using
  %defines.  For example:

    %defines "parser.h"

** When reporting useless rules, useless nonterminals, and unused terminals,
  Bison now employs the terms "useless in grammar" instead of "useless",
  "useless in parser" instead of "never reduced", and "unused in grammar"
  instead of "unused".

** Unreachable State Removal

  Previously, Bison sometimes generated parser tables containing unreachable
  states.  A state can become unreachable during conflict resolution if Bison
  disables a shift action leading to it from a predecessor state.  Bison now:

    1. Removes unreachable states.

    2. Does not report any conflicts that appeared in unreachable states.
       WARNING: As a result, you may need to update %expect and %expect-rr
       directives in existing grammar files.

    3. For any rule used only in such states, Bison now reports the rule as
       "useless in parser due to conflicts".

  This feature can be disabled with the following directive:

    %define lr.keep_unreachable_states

  See the %define entry in the `Bison Declaration Summary' in the Bison manual
  for further discussion.

** Lookahead Set Correction in the `.output' Report

  When instructed to generate a `.output' file including lookahead sets
  (using `--report=lookahead', for example), Bison now prints each reduction's
  lookahead set only next to the associated state's one item that (1) is
  associated with the same rule as the reduction and (2) has its dot at the end
  of its RHS.  Previously, Bison also erroneously printed the lookahead set
  next to all of the state's other items associated with the same rule.  This
  bug affected only the `.output' file and not the generated parser source
  code.

** --report-file=FILE is a new option to override the default `.output' file
  name.

** The `=' that used to be required in the following directives is now
  deprecated:

    %file-prefix "parser"
    %name-prefix "c_"
    %output "parser.c"

** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'

  Bison 2.3a provided a new set of directives as a more flexible alternative to
  the traditional Yacc prologue blocks.  Those have now been consolidated into
  a single %code directive with an optional qualifier field, which identifies
  the purpose of the code and thus the location(s) where Bison should generate
  it:

    1. `%code          {CODE}' replaces `%after-header  {CODE}'
    2. `%code requires {CODE}' replaces `%start-header  {CODE}'
    3. `%code provides {CODE}' replaces `%end-header    {CODE}'
    4. `%code top      {CODE}' replaces `%before-header {CODE}'

  See the %code entries in section `Bison Declaration Summary' in the Bison
  manual for a summary of the new functionality.  See the new section `Prologue
  Alternatives' for a detailed discussion including the advantages of %code
  over the traditional Yacc prologues.

  The prologue alternatives are experimental.  More user feedback will help to
  determine whether they should become permanent features.

** Revised warning: unset or unused mid-rule values

  Since Bison 2.2, Bison has warned about mid-rule values that are set but not
  used within any of the actions of the parent rule.  For example, Bison warns
  about unused $2 in:

    exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };

  Now, Bison also warns about mid-rule values that are used but not set.  For
  example, Bison warns about unset $$ in the mid-rule action in:

    exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };

  However, Bison now disables both of these warnings by default since they
  sometimes prove to be false alarms in existing grammars employing the Yacc
  constructs $0 or $-N (where N is some positive integer).

  To enable these warnings, specify the option `--warnings=midrule-values' or
  `-W', which is a synonym for `--warnings=all'.

** Default %destructor or %printer with `<*>' or `<>'

  Bison now recognizes two separate kinds of default %destructor's and
  %printer's:

    1. Place `<*>' in a %destructor/%printer symbol list to define a default
       %destructor/%printer for all grammar symbols for which you have formally
       declared semantic type tags.

    2. Place `<>' in a %destructor/%printer symbol list to define a default
       %destructor/%printer for all grammar symbols without declared semantic
       type tags.

  Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
  `<*>' and `<>' combined achieve the same effect with one exception: Bison no
  longer applies any %destructor to a mid-rule value if that mid-rule value is
  not actually ever referenced using either $$ or $n in a semantic action.

  The default %destructor's and %printer's are experimental.  More user
  feedback will help to determine whether they should become permanent
  features.

  See the section `Freeing Discarded Symbols' in the Bison manual for further
  details.

** %left, %right, and %nonassoc can now declare token numbers.  This is required
  by POSIX.  However, see the end of section `Operator Precedence' in the Bison
  manual for a caveat concerning the treatment of literal strings.

** The nonfunctional --no-parser, -n, and %no-parser options have been
  completely removed from Bison.

* Changes in version 2.3a, 2006-09-13:

** Instead of %union, you can define and use your own union type
  YYSTYPE if your grammar contains at least one <type> tag.
  Your YYSTYPE need not be a macro; it can be a typedef.
  This change is for compatibility with other Yacc implementations,
  and is required by POSIX.

** Locations columns and lines start at 1.
  In accordance with the GNU Coding Standards and Emacs.

** You may now declare per-type and default %destructor's and %printer's:

  For example:

    %union { char *string; }
    %token <string> STRING1
    %token <string> STRING2
    %type  <string> string1
    %type  <string> string2
    %union { char character; }
    %token <character> CHR
    %type  <character> chr
    %destructor { free ($$); } %symbol-default
    %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
    %destructor { } <character>

  guarantees that, when the parser discards any user-defined symbol that has a
  semantic type tag other than `<character>', it passes its semantic value to
  `free'.  However, when the parser discards a `STRING1' or a `string1', it
  also prints its line number to `stdout'.  It performs only the second
  `%destructor' in this case, so it invokes `free' only once.

  [Although we failed to mention this here in the 2.3a release, the default
  %destructor's and %printer's were experimental, and they were rewritten in
  future versions.]

** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
  `--yacc', or `%yacc'), Bison no longer generates #define statements for
  associating token numbers with token names.  Removing the #define statements
  helps to sanitize the global namespace during preprocessing, but POSIX Yacc
  requires them.  Bison still generates an enum for token names in all cases.

** Handling of traditional Yacc prologue blocks is now more consistent but
  potentially incompatible with previous releases of Bison.

  As before, you declare prologue blocks in your grammar file with the
  `%{ ... %}' syntax.  To generate the pre-prologue, Bison concatenates all
  prologue blocks that you've declared before the first %union.  To generate
  the post-prologue, Bison concatenates all prologue blocks that you've
  declared after the first %union.

  Previous releases of Bison inserted the pre-prologue into both the header
  file and the code file in all cases except for LALR(1) parsers in C.  In the
  latter case, Bison inserted it only into the code file.  For parsers in C++,
  the point of insertion was before any token definitions (which associate
  token numbers with names).  For parsers in C, the point of insertion was
  after the token definitions.

  Now, Bison never inserts the pre-prologue into the header file.  In the code
  file, it always inserts it before the token definitions.

** Bison now provides a more flexible alternative to the traditional Yacc
  prologue blocks: %before-header, %start-header, %end-header, and
  %after-header.

  For example, the following declaration order in the grammar file reflects the
  order in which Bison will output these code blocks.  However, you are free to
  declare these code blocks in your grammar file in whatever order is most
  convenient for you:

    %before-header {
      /* Bison treats this block like a pre-prologue block: it inserts it into
       * the code file before the contents of the header file.  It does *not*
       * insert it into the header file.  This is a good place to put
       * #include's that you want at the top of your code file.  A common
       * example is `#include "system.h"'.  */
    }
    %start-header {
      /* Bison inserts this block into both the header file and the code file.
       * In both files, the point of insertion is before any Bison-generated
       * token, semantic type, location type, and class definitions.  This is a
       * good place to define %union dependencies, for example.  */
    }
    %union {
      /* Unlike the traditional Yacc prologue blocks, the output order for the
       * new %*-header blocks is not affected by their declaration position
       * relative to any %union in the grammar file.  */
    }
    %end-header {
      /* Bison inserts this block into both the header file and the code file.
       * In both files, the point of insertion is after the Bison-generated
       * definitions.  This is a good place to declare or define public
       * functions or data structures that depend on the Bison-generated
       * definitions.  */
    }
    %after-header {
      /* Bison treats this block like a post-prologue block: it inserts it into
       * the code file after the contents of the header file.  It does *not*
       * insert it into the header file.  This is a good place to declare or
       * define internal functions or data structures that depend on the
       * Bison-generated definitions.  */
    }

  If you have multiple occurrences of any one of the above declarations, Bison
  will concatenate the contents in declaration order.

  [Although we failed to mention this here in the 2.3a release, the prologue
  alternatives were experimental, and they were rewritten in future versions.]

** The option `--report=look-ahead' has been changed to `--report=lookahead'.
  The old spelling still works, but is not documented and may be removed
  in a future release.


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