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[bison.git] / NEWS

Bison News
----------

Changes in version 1.49b:

* GLR parsing
  The declaration
     %glr-parser
  causes Bison to produce a Generalized LR (GLR) parser, capable of handling
  almost any context-free grammar, ambiguous or not.  The new declarations
  %dprec and %merge on grammar rules allow parse-time resolution of
  ambiguities.  Contributed by Paul Hilfinger.

* Output Directory
  When not in Yacc compatibility mode, when the output file was not
  specified, runnning `bison foo/bar.y' created `foo/bar.c'.  It
  now creates `bar.c'.

* Undefined token
  The undefined token was systematically mapped to 2 which prevented
  the use of 2 from the user.  This is no longer the case.

* Unknown token numbers
  If yylex returned a code out of range, yyparse could die.  This is
  no longer the case.

* Error token
  According to POSIX, the error token should be numbered as 256.
  Bison extends this requirement by making it a preference: *if* the
  user specified that one of her tokens is numbered 256, then error
  will be mapped onto another number.

* Verbose error messages
  They no longer report `..., expecting error or...' for state where
  error recovery is possible.

* End token
  Defaults to `$end' instead of `$'.

* Error recovery now conforms to documentation and to POSIX
  When a Bison-generated parser encounters a syntax error, it now pops
  the stack until it finds a state that allows shifting the error
  token.  Formerly, it popped the stack until it found a state that
  allowed some non-error action other than a default reduction on the
  error token.  The new behavior has long been the documented behavior,
  and has long been required by POSIX.  For more details, please see
  <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.

* Traces
  Popped tokens and nonterminals are now reported.

* Large grammars
  Large grammars are now supported (large token numbers, large grammar
  size (= sum of the LHS and RHS lengths), large LALR tables).

* Explicit initial rule
  Bison used to play hacks with the initial rule, which the user does
  not write.  It is now explicit, and visible in the reports and
  graphs as rule 0.

* Useless rules
  Before, Bison reported the useless rules, but, although not used,
  included them in the parsers.  They are now actually removed.

* Useless rules, useless nonterminals
  They are now reported, as a warning, with their locations.

* Rules never reduced
  Rules that can never be reduced because of conflicts are now
  reported.

* Incorrect `Token not used'
  On a grammar such as

           %token useless useful
           %%
           exp: '0' %prec useful;

  where a token was used to set the precedence of the last rule,
  bison reported both `useful' and `useless' as useless tokens.

* Revert the C++ namespace changes introduced in 1.31
  as they caused too many portability hassles.

* Default locations
  By an accident of design, the default computation of @$ was
  performed after another default computation was performed: @$ = @1.
  The latter is now removed: YYLLOC_DEFAULT is fully responsible of
  the computation of @$.

* Token end-of-file
  The token end of file may be specified by the user, in which case,
  the user symbol is used in the reports, the graphs, and the verbose
  error messages instead of `$end', which remains being the defaults.
  For instance
     %token YYEOF 0
  or
     %token YYEOF 0 "end of file"

* Semantic parser
  This old option, which has been broken for ages, is removed.

* New translation
  Croatian, thanks to Denis Lackovic.

* Incorrect token definitions
  When fed with `%token 'a' "A"', Bison used to output `#define 'a' 65'.

* Token definitions as enums
  Tokens are output both as the traditional #define's, and, provided
  the compiler supports ANSI C or is a C++ compiler, as enums.
  This helps debuggers producing symbols instead of values.

* Reports
  In addition to --verbose, bison supports --report=THINGS, which
  produces additional information:
  - itemset
    complete the core item sets with their closure
  - lookahead
    explicitly associate lookaheads to items
  - solved
    describe shift/reduce conflicts solving.
    Bison used to systematically output this information on top of
    the report.  Solved conflicts are now attached to their states.

* Type clashes
  Previous versions don't complain when there is a type clash on
  the default action if the rule has a mid-rule action, such as in:

      %type <foo> bar
      %%
      bar: '0' {} '0';

  This is fixed.
\f
Changes in version 1.35, 2002-03-25:

* C Skeleton
  Some projects use Bison's C parser with C++ compilers, and define
  YYSTYPE as a class.  The recent adjustment of C parsers for data
  alignment and 64 bit architectures made this impossible.

  Because for the time being no real solution for C++ parser
  generation exists, kludges were implemented in the parser to
  maintain this use.  In the future, when Bison has C++ parsers, this
  kludge will be disabled.

  This kludge also addresses some C++ problems when the stack was
  extended.

\f
Changes in version 1.34, 2002-03-12:

* File name clashes are detected
  $ bison foo.y -d -o foo.x
  fatal error: header and parser would both be named `foo.x'

* A missing `;' at the end of a rule triggers a warning
  In accordance with POSIX, and in agreement with other
  Yacc implementations, Bison will mandate this semicolon in the near
  future.  This eases the implementation of a Bison parser of Bison
  grammars by making this grammar LALR(1) instead of LR(2).  To
  facilitate the transition, this release introduces a warning.

* Revert the C++ namespace changes introduced in 1.31, as they caused too
  many portability hassles.

* DJGPP support added.

* Fix test suite portability problems.
\f
Changes in version 1.33, 2002-02-07:

* Fix C++ issues
  Groff could not be compiled for the definition of size_t was lacking
  under some conditions.

* Catch invalid @n
  As is done with $n.
\f
Changes in version 1.32, 2002-01-23:

* Fix Yacc output file names

* Portability fixes

* Italian, Dutch translations
\f
Changes in version 1.31, 2002-01-14:

* Many Bug Fixes

* GNU Gettext and %expect
  GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
  Bison dies on incorrect %expectations, we fear there will be
  too many bug reports for Gettext, so _for the time being_, %expect
  does not trigger an error when the input file is named `plural.y'.

* Use of alloca in parsers
  If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
  malloc exclusively.  Since 1.29, but was not NEWS'ed.

  alloca is used only when compiled with GCC, to avoid portability
  problems as on AIX.

* When the generated parser lacks debugging code, YYDEBUG is now 0
  (as POSIX requires) instead of being undefined.

* User Actions
  Bison has always permitted actions such as { $$ = $1 }: it adds the
  ending semicolon.  Now if in Yacc compatibility mode, the semicolon
  is no longer output: one has to write { $$ = $1; }.

* Better C++ compliance
  The output parsers try to respect C++ namespaces.
  [This turned out to be a failed experiment, and it was reverted later.]

* Reduced Grammars
  Fixed bugs when reporting useless nonterminals.

* 64 bit hosts
  The parsers work properly on 64 bit hosts.

* Error messages
  Some calls to strerror resulted in scrambled or missing error messages.

* %expect
  When the number of shift/reduce conflicts is correct, don't issue
  any warning.

* The verbose report includes the rule line numbers.

* Rule line numbers are fixed in traces.

* Swedish translation

* Parse errors
  Verbose parse error messages from the parsers are better looking.
  Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
     Now: parse error: unexpected '/', expecting "number" or '-' or '('

* Fixed parser memory leaks.
  When the generated parser was using malloc to extend its stacks, the
  previous allocations were not freed.

* Fixed verbose output file.
  Some newlines were missing.
  Some conflicts in state descriptions were missing.

* Fixed conflict report.
  Option -v was needed to get the result.

* %expect
  Was not used.
  Mismatches are errors, not warnings.

* Fixed incorrect processing of some invalid input.

* Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.

* Fixed some typos in the documentation.

* %token MY_EOF 0 is supported.
  Before, MY_EOF was silently renumbered as 257.

* doc/refcard.tex is updated.

* %output, %file-prefix, %name-prefix.
  New.

* --output
  New, aliasing `--output-file'.
\f
Changes in version 1.30, 2001-10-26:

* `--defines' and `--graph' have now an optionnal argument which is the
  output file name. `-d' and `-g' do not change, they do not take any
  argument.

* `%source_extension' and `%header_extension' are removed, failed
  experiment.

* Portability fixes.
\f
Changes in version 1.29, 2001-09-07:

* The output file does not define const, as this caused problems when used
  with common autoconfiguration schemes.  If you still use ancient compilers
  that lack const, compile with the equivalent of the C compiler option
  `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.

* Added `-g' and `--graph'.

* The Bison manual is now distributed under the terms of the GNU FDL.

* The input and the output files has automatically a similar extension.

* Russian translation added.

* NLS support updated; should hopefully be less troublesome.

* Added the old Bison reference card.

* Added `--locations' and `%locations'.

* Added `-S' and `--skeleton'.

* `%raw', `-r', `--raw' is disabled.

* Special characters are escaped when output.  This solves the problems
  of the #line lines with path names including backslashes.

* New directives.
  `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
  `%debug', `%source_extension' and `%header_extension'.

* @$
  Automatic location tracking.
\f
Changes in version 1.28, 1999-07-06:

* Should compile better now with K&R compilers.

* Added NLS.

* Fixed a problem with escaping the double quote character.

* There is now a FAQ.
\f
Changes in version 1.27:

* The make rule which prevented bison.simple from being created on
  some systems has been fixed.
\f
Changes in version 1.26:

* Bison now uses automake.

* New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.

* Token numbers now start at 257 as previously documented, not 258.

* Bison honors the TMPDIR environment variable.

* A couple of buffer overruns have been fixed.

* Problems when closing files should now be reported.

* Generated parsers should now work even on operating systems which do
  not provide alloca().
\f
Changes in version 1.25, 1995-10-16:

* Errors in the input grammar are not fatal; Bison keeps reading
the grammar file, and reports all the errors found in it.

* Tokens can now be specified as multiple-character strings: for
example, you could use "<=" for a token which looks like <=, instead
of chosing a name like LESSEQ.

* The %token_table declaration says to write a table of tokens (names
and numbers) into the parser file.  The yylex function can use this
table to recognize multiple-character string tokens, or for other
purposes.

* The %no_lines declaration says not to generate any #line preprocessor
directives in the parser file.

* The %raw declaration says to use internal Bison token numbers, not
Yacc-compatible token numbers, when token names are defined as macros.

* The --no-parser option produces the parser tables without including
the parser engine; a project can now use its own parser engine.
The actions go into a separate file called NAME.act, in the form of
a switch statement body.
\f
Changes in version 1.23:

The user can define YYPARSE_PARAM as the name of an argument to be
passed into yyparse.  The argument should have type void *.  It should
actually point to an object.  Grammar actions can access the variable
by casting it to the proper pointer type.

Line numbers in output file corrected.
\f
Changes in version 1.22:

--help option added.
\f
Changes in version 1.20:

Output file does not redefine const for C++.

Local Variables:
mode: outline
End:

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