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Bison 2.2 released

From: Paul Eggert
Subject: Bison 2.2 released
Date: Fri, 19 May 2006 16:18:16 -0700

Bison version 2.2 has been released.

Aside from bug fixes, the most important changes in Bison 2.2 are in
the new parser skeletons, used to generate parsers other than the
traditional Yacc-like parsers.  Among other things, the distribution
terms now permit using Bison-generated parsers in nonfree programs;
previously this was allowed only for Yacc-like parsers.  For more
details please see the end of this message.

Bison is a parser generator that is compatible with Yacc.
Please see <> for more info.

Here are the URLs for the gzip and bzip2 compressed tar images:

Here are their MD5 and SHA1 checksums, respectively:

4b0ebf57fe935d7d5cc01907d1400b8b  bison-2.2.tar.gz
e345a5d021db850f06ce49eba78af027  bison-2.2.tar.bz2
5dfad03a9c651c4d24a4a389af3549dd52ef0f6f  bison-2.2.tar.gz
b01691c83cc0d08d3c03e32c494f6b03381ecd21  bison-2.2.tar.bz2

To try this version, please make sure you have GNU m4 1.4.4 installed.
Then obtain the file bison-2.2.tar.gz, and execute the following shell
commands or their equivalents:

   gunzip <bison-2.2.tar.gz | tar xf -
   cd bison-2.2
   make check

We particularly appreciate tests on unusual hosts.
Please report bugs to <address@hidden>.

As usual, thanks to everyone who has contributed bug reports and
improvements to Bison.

Here is a list of user-visible changes in version 2.2, as compared to 2.1.

* The distribution terms for all Bison-generated parsers now permit
  using the parsers in nonfree programs.  Previously, this permission
  was granted only for Bison-generated LALR(1) parsers in C.

* %name-prefix changes the namespace name in C++ outputs.

* The C++ parsers export their token_type.

* Bison now allows multiple %union declarations, and concatenates
  their contents together.

* New warning: unused values
  Right-hand side symbols whose values are not used are reported,
  if the symbols have destructors.  For instance:

     exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
        | exp "+" exp

  will trigger a warning about $$ and $5 in the first rule, and $3 in
  the second ($1 is copied to $$ by the default rule).  This example
  most likely contains three errors, and could be rewritten as:

     exp: exp "?" exp ":" exp
            { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
        | exp "+" exp
            { $$ = $1 ? $1 : $3; if ($1) free ($3); }

  However, if the original actions were really intended, memory leaks
  and all, the warnings can be suppressed by letting Bison believe the
  values are used, e.g.:

     exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
        | exp "+" exp         { $$ = $1; (void) $3; }

  If there are mid-rule actions, the warning is issued if no action
  uses it.  The following triggers no warning: $1 and $3 are used.

     exp: exp { push ($1); } '+' exp { push ($3); sum (); };

  The warning is intended to help catching lost values and memory leaks.
  If a value is ignored, its associated memory typically is not reclaimed.

* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
  Destructors are now called when user code invokes YYABORT, YYACCEPT,
  and YYERROR, for all objects on the stack, other than objects
  corresponding to the right-hand side of the current rule.

* %expect, %expect-rr
  Incorrect numbers of expected conflicts are now actual errors,
  instead of warnings.

* GLR, YACC parsers.
  The %parse-params are available in the destructors (and the
  experimental printers) as per the documentation.

* Bison now warns if it finds a stray `$' or `@' in an action.

* %require "VERSION"
  This specifies that the grammar file depends on features implemented
  in Bison version VERSION or higher.

* The token and value types are now class members.
  The tokens were defined as free form enums and cpp macros.  YYSTYPE
  was defined as a free form union.  They are now class members:
  tokens are enumerations of the `yy::parser::token' struct, and the
  semantic values have the `yy::parser::semantic_type' type.

  If you do not want or can update to this scheme, the directive
  `%define "global_tokens_and_yystype" "1"' triggers the global
  definition of tokens and YYSTYPE.  This change is suitable both
  for previous releases of Bison, and this one.

  If you wish to update, then make sure older version of Bison will
  fail using `%require "2.2"'.

* DJGPP support added.

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