Bison test version 2.1a released

[Paul Eggert]

Bison test version 2.1a is now available.  It contains mostly bug
fixes for Bison 2.1, but there are few new features, notably in the
area of better support for destructors.  Our intention is to generate
a new official release soon, based on feedback from this test version.

Here is the URL:

ftp://alpha.gnu.org/gnu/bison/bison-2.1a.tar.gz

Here is the MD5 checksum:

021d6072cf0dea923b54d19ab3c2ced0  bison-2.1a.tar.gz

To try this test version, please make sure you have GNU m4 1.4.4
<ftp://ftp.gnu.org/gnu/m4/m4-1.4.4.tar.gz> installed, and then execute
the following shell commands or their equivalents:

   wget ftp://alpha.gnu.org/gnu/bison/bison-2.1a.tar.gz
   gunzip <bison-2.1a.tar.gz | tar xf -
   cd bison-2.1a
   ./configure
   make
   make check

We particularly appreciate tests on unusual hosts.

Please report bugs to <address@hidden>.

Bison is a parser generator that is compatible with Yacc.
Please see <http://www.gnu.org/software/bison/> for more info about Bison.

Here is a list of user-visible changes in version 2.1a, compared to 2.1:

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

* New warning: unused values
  Typed right-hand side symbols whose values are not used are reported,
  if the associated types 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.

* lalr1.cc: 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 "2.1a"'.

* DJGPP support added.