doc: don't use @acronym.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 3d5a561b09ecfb3af4603ca88a3b314aa8f0e903..593807c7987c6552ce16bc7d5c59eca72c306c0b 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,7 +3,22 @@ Bison News
 
 * Changes in version ?.? (????-??-??):
 
 
 * Changes in version ?.? (????-??-??):
 

-** Java skeleton improvements:
+** Additional yylex/yyparse arguments
+
+  The new directive %param declare additional argument to both yylex
+  and yyparse.  The %lex-param, %parse-param, and %param directives
+  support one or more arguments.  Instead of
+
+      %lex-param   {arg1_type *arg1}
+      %lex-param   {arg2_type *arg2}
+      %parse-param {arg1_type *arg1}
+      %parse-param {arg2_type *arg2}
+
+  one may now declare
+
+      %param {arg1_type *arg1} {arg2_type *arg2}
+
+** Java skeleton improvements

 
   The constants for token names were moved to the Lexer interface.
   Also, it is possible to add code to the parser's constructors using
 
   The constants for token names were moved to the Lexer interface.
   Also, it is possible to add code to the parser's constructors using


@@ -25,15 +40,60 @@ Bison News
   use these prefixed token names, although the grammar itself still
   uses the short names (as in the sample rule given above).
 
   use these prefixed token names, although the grammar itself still
   uses the short names (as in the sample rule given above).
 

+** Variable api.namespace
+
+  The "namespace" variable is renamed "api.namespace".  Backward
+  compatibility is ensured, but upgrading is recommended.
+
+** Variable parse.error
+
+  The variable error controls the verbosity of error messages.  The
+  use of the %error-verbose directive is deprecated in favor of
+  %define parse.error "verbose".
+
+** Semantic predicates
+
+  The new, experimental, semantic-predicate feature allows actions of
+  the form %?{ BOOLEAN-EXPRESSION }, which cause syntax errors (as for
+  YYERROR) if the expression evaluates to 0, and are evaluated immediately
+  in GLR parsers, rather than being deferred.  The result is that they
+  allow the programmer to prune possible parses based on the values of
+  runtime expressions.
+

 * Changes in version 2.5 (????-??-??):
 
 * Changes in version 2.5 (????-??-??):
 

-** IELR(1) and Canonical LR(1) Support
+** Named references:
+
+  Historically, Yacc and Bison have supported positional references
+  ($n, $$) to allow access to symbol values from inside of semantic
+  actions code.
+
+  Starting from this version, Bison can also accept named references.
+  When no ambiguity is possible, original symbol names may be used
+  as named references:
+
+    if_stmt : 'if' cond_expr 'then' then_stmt ';'
+    { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
+
+  In the more common case, explicit names may be declared:
+
+    stmt[res] : 'if' expr[cond] 'then' stmt[then] 'else' stmt[else] ';'
+    { $res = mk_if_stmt($cond, $then, $else); }
+
+  Location information is also accessible using @name syntax.  When
+  accessing symbol names containing dots or dashes, explicit bracketing
+  ($[sym.1]) must be used.
+
+  These features are experimental in this version.  More user feedback
+  will help to stabilize them.
+
+** IELR(1) and canonical LR(1):

 
   IELR(1) is a minimal LR(1) parser table generation algorithm.  That
   is, given any context-free grammar, IELR(1) generates parser tables
   with the full language recognition power of canonical LR(1) but with
 
   IELR(1) is a minimal LR(1) parser table generation algorithm.  That
   is, given any context-free grammar, IELR(1) generates parser tables
   with the full language recognition power of canonical LR(1) but with

-  nearly the same number of parser states as LALR(1).  This reduction in
-  parser states is often an order of magnitude.  More importantly,
+  nearly the same number of parser states as LALR(1).  This reduction
+  in parser states is often an order of magnitude.  More importantly,

   because canonical LR(1)'s extra parser states may contain duplicate
   conflicts in the case of non-LR(1) grammars, the number of conflicts
   for IELR(1) is often an order of magnitude less as well.  This can
   because canonical LR(1)'s extra parser states may contain duplicate
   conflicts in the case of non-LR(1) grammars, the number of conflicts
   for IELR(1) is often an order of magnitude less as well.  This can


@@ -44,9 +104,9 @@ Bison News
   default.  You can specify the type of parser tables in the grammar
   file with these directives:
 
   default.  You can specify the type of parser tables in the grammar
   file with these directives:
 

-    %define lr.type "LALR"
-    %define lr.type "IELR"
-    %define lr.type "canonical LR"
+    %define lr.type lalr
+    %define lr.type ielr
+    %define lr.type canonical-lr

 
   The default reduction optimization in the parser tables can also be
   adjusted using `%define lr.default-reductions'.  See the documentation
 
   The default reduction optimization in the parser tables can also be
   adjusted using `%define lr.default-reductions'.  See the documentation


@@ -57,7 +117,57 @@ Bison News
   These features are experimental.  More user feedback will help to
   stabilize them.
 
   These features are experimental.  More user feedback will help to
   stabilize them.
 

-** %define can now be invoked via the command line.
+** LAC (lookahead correction) for syntax error handling:
+
+  Canonical LR, IELR, and LALR can suffer from a couple of problems
+  upon encountering a syntax error.  First, the parser might perform
+  additional parser stack reductions before discovering the syntax
+  error.  Such reductions perform user semantic actions that are
+  unexpected because they are based on an invalid token, and they
+  cause error recovery to begin in a different syntactic context than
+  the one in which the invalid token was encountered.  Second, when
+  verbose error messages are enabled (with %error-verbose or `#define
+  YYERROR_VERBOSE'), the expected token list in the syntax error
+  message can both contain invalid tokens and omit valid tokens.
+
+  The culprits for the above problems are %nonassoc, default
+  reductions in inconsistent states, and parser state merging.  Thus,
+  IELR and LALR suffer the most.  Canonical LR can suffer only if
+  %nonassoc is used or if default reductions are enabled for
+  inconsistent states.
+
+  LAC is a new mechanism within the parsing algorithm that completely
+  solves these problems for canonical LR, IELR, and LALR without
+  sacrificing %nonassoc, default reductions, or state mering.  When
+  LAC is in use, canonical LR and IELR behave exactly the same for
+  both syntactically acceptable and syntactically unacceptable input.
+  While LALR still does not support the full language-recognition
+  power of canonical LR and IELR, LAC at least enables LALR's syntax
+  error handling to correctly reflect LALR's language-recognition
+  power.
+
+  Currently, LAC is only supported for deterministic parsers in C.
+  You can enable LAC with the following directive:
+
+    %define parse.lac full
+
+  See the documentation for `%define parse.lac' in the section `Bison
+  Declaration Summary' in the Bison manual for additional details.
+
+  LAC is an experimental feature.  More user feedback will help to
+  stabilize it.
+
+** Grammar symbol names can now contain dashes:
+
+  Consistently with directives (such as %error-verbose) and variables
+  (e.g. push-pull), grammar symbol names may include dashes in any
+  position, similarly to periods and underscores.  This is GNU
+  extension over POSIX Yacc whose use is reported by -Wyacc, and
+  rejected in Yacc mode (--yacc).
+
+** %define improvements:
+
+*** Can now be invoked via the command line:

 
   Each of these command-line options
 
 
   Each of these command-line options
 


@@ -76,7 +186,7 @@ Bison News
   quietly override %define, but -D and --define do not.  For further
   details, see the section "Bison Options" in the Bison manual.
 
   quietly override %define, but -D and --define do not.  For further
   details, see the section "Bison Options" in the Bison manual.
 

-** %define variables renamed.
+*** Variables renamed:

 
   The following %define variables
 
 
   The following %define variables
 


@@ -91,15 +201,97 @@ Bison News
   The old names are now deprecated but will be maintained indefinitely
   for backward compatibility.
 
   The old names are now deprecated but will be maintained indefinitely
   for backward compatibility.
 

-** Symbols names
+*** Values no longer need to be quoted in grammar file:

 
 

-  Consistently with directives (such as %error-verbose) and variables
-  (e.g. push-pull), symbol names may include dashes in any position,
-  similarly to periods and underscores.  This is GNU extension over
-  POSIX Yacc whose use is reported by -Wyacc, and rejected in Yacc
-  mode (--yacc).
+  If a %define value is an identifier, it no longer needs to be placed
+  within quotations marks.  For example,

 
 

-** Temporary hack for adding a semicolon to the user action.
+    %define api.push-pull "push"
+
+  can be rewritten as
+
+    %define api.push-pull push
+
+*** Unrecognized variables are now errors not warnings.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+** Unrecognized %code qualifiers are now errors not warnings.
+
+** Character literals not of length one:
+
+  Previously, Bison quietly converted all character literals to length
+  one.  For example, without warning, Bison interpreted the operators in
+  the following grammar to be the same token:
+
+    exp: exp '++'
+       | exp '+' exp
+       ;
+
+  Bison now warns when a character literal is not of length one.  In
+  some future release, Bison will start reporting an error instead.
+
+** Destructor calls fixed for lookaheads altered in semantic actions:
+
+  Previously for deterministic parsers in C, if a user semantic action
+  altered yychar, the parser in some cases used the old yychar value to
+  determine which destructor to call for the lookahead upon a syntax
+  error or upon parser return.  This bug has been fixed.
+
+** C++ parsers use YYRHSLOC:
+
+  Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
+  macro and use it in the default YYLLOC_DEFAULT.  You are encouraged
+  to use it.  If, for instance, your location structure has "first"
+  and "last" members, instead of
+
+      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+        do                                                                 \
+          if (N)                                                           \
+            {                                                              \
+              (Current).first = (Rhs)[1].location.first;                   \
+              (Current).last  = (Rhs)[N].location.last;                    \
+            }                                                              \
+          else                                                             \
+            {                                                              \
+              (Current).first = (Current).last = (Rhs)[0].location.last;   \
+            }                                                              \
+        while (false)
+
+  use:
+
+      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+        do                                                                 \
+          if (N)                                                           \
+            {                                                              \
+              (Current).first = YYRHSLOC (Rhs, 1).first;                   \
+              (Current).last  = YYRHSLOC (Rhs, N).last;                    \
+            }                                                              \
+          else                                                             \
+            {                                                              \
+              (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last;   \
+            }                                                              \
+        while (false)
+
+** YYLLOC_DEFAULT in C++:
+
+  The default implementation of YYLLOC_DEFAULT used to be issued in
+  the header file.  It is now output in the implementation file, after
+  the user %code sections so that its #ifndef guard does not try to
+  override the user's YYLLOC_DEFAULT if provided.
+
+** YYFAIL now produces warnings and Java parsers no longer implement it:
+
+  YYFAIL has existed for many years as an undocumented feature of
+  deterministic parsers in C generated by Bison.  More recently, it was
+  a documented feature of Bison's experimental Java parsers.  As
+  promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
+  semantic action now produces a deprecation warning, and Java parsers
+  no longer implement YYFAIL at all.  For further details, including a
+  discussion of how to suppress C preprocessor warnings about YYFAIL
+  being unused, see the Bison 2.4.2 NEWS entry.
+
+** Temporary hack for adding a semicolon to the user action:

 
   Previously, Bison appended a semicolon to every user action for
   reductions when the output language defaulted to C (specifically, when
 
   Previously, Bison appended a semicolon to every user action for
   reductions when the output language defaulted to C (specifically, when


@@ -120,7 +312,89 @@ Bison News
   about a missing semicolon where it did not before.  Future releases of
   Bison will cease to append semicolons entirely.
 
   about a missing semicolon where it did not before.  Future releases of
   Bison will cease to append semicolons entirely.
 

-* Changes in version 2.4.2 (????-??-??):
+** Verbose syntax error message fixes:
+
+  When %error-verbose or `#define YYERROR_VERBOSE' is specified,
+  syntax error messages produced by the generated parser include the
+  unexpected token as well as a list of expected tokens.  The effect
+  of %nonassoc on these verbose messages has been corrected in two
+  ways, but a complete fix requires LAC, described above:
+
+*** When %nonassoc is used, there can exist parser states that accept no
+    tokens, and so the parser does not always require a lookahead token
+    in order to detect a syntax error.  Because no unexpected token or
+    expected tokens can then be reported, the verbose syntax error
+    message described above is suppressed, and the parser instead
+    reports the simpler message, "syntax error".  Previously, this
+    suppression was sometimes erroneously triggered by %nonassoc when a
+    lookahead was actually required.  Now verbose messages are
+    suppressed only when all previous lookaheads have already been
+    shifted or discarded.
+
+*** Previously, the list of expected tokens erroneously included tokens
+    that would actually induce a syntax error because conflicts for them
+    were resolved with %nonassoc in the current parser state.  Such
+    tokens are now properly omitted from the list.
+
+*** Expected token lists are still often wrong due to state merging
+    (from LALR or IELR) and default reductions, which can both add
+    invalid tokens and subtract valid tokens.  Canonical LR almost
+    completely fixes this problem by eliminating state merging and
+    default reductions.  However, there is one minor problem left even
+    when using canonical LR and even after the fixes above.  That is,
+    if the resolution of a conflict with %nonassoc appears in a later
+    parser state than the one at which some syntax error is
+    discovered, the conflicted token is still erroneously included in
+    the expected token list.  Bison's new LAC implementation,
+    described above, eliminates this problem and the need for
+    canonical LR.  However, LAC is still experimental and is disabled
+    by default.
+
+* Changes in version 2.4.3 (2010-08-05):
+
+** Bison now obeys -Werror and --warnings=error for warnings about
+   grammar rules that are useless in the parser due to conflicts.
+
+** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
+   been fixed.
+
+** Failures in the test suite for GCC 4.5 have been fixed.
+
+** Failures in the test suite for some versions of Sun Studio C++ have
+   been fixed.
+
+** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
+   warnings about undefined %prec identifiers will not be converted to
+   errors in Bison 2.5.  They will remain warnings, which should be
+   sufficient for POSIX while avoiding backward compatibility issues.
+
+** Minor documentation fixes.
+
+* Changes in version 2.4.2 (2010-03-20):
+
+** Some portability problems that resulted in failures and livelocks
+   in the test suite on some versions of at least Solaris, AIX, HP-UX,
+   RHEL4, and Tru64 have been addressed.  As a result, fatal Bison
+   errors should no longer cause M4 to report a broken pipe on the
+   affected platforms.
+
+** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
+
+  POSIX specifies that an error be reported for any identifier that does
+  not appear on the LHS of a grammar rule and that is not defined by
+  %token, %left, %right, or %nonassoc.  Bison 2.3b and later lost this
+  error report for the case when an identifier appears only after a
+  %prec directive.  It is now restored.  However, for backward
+  compatibility with recent Bison releases, it is only a warning for
+  now.  In Bison 2.5 and later, it will return to being an error.
+  [Between the 2.4.2 and 2.4.3 releases, it was decided that this
+  warning will not be converted to an error in Bison 2.5.]
+
+** Detection of GNU M4 1.4.6 or newer during configure is improved.
+
+** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
+   YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
+   avoided.

 
 ** %code is now a permanent feature.
 
 
 ** %code is now a permanent feature.
 


@@ -145,6 +419,51 @@ Bison News
   Bison's Java feature as a whole including its current usage of %code
   is still considered experimental.
 
   Bison's Java feature as a whole including its current usage of %code
   is still considered experimental.
 

+** YYFAIL is deprecated and will eventually be removed.
+
+  YYFAIL has existed for many years as an undocumented feature of
+  deterministic parsers in C generated by Bison.  Previously, it was
+  documented for Bison's experimental Java parsers.  YYFAIL is no longer
+  documented for Java parsers and is formally deprecated in both cases.
+  Users are strongly encouraged to migrate to YYERROR, which is
+  specified by POSIX.
+
+  Like YYERROR, you can invoke YYFAIL from a semantic action in order to
+  induce a syntax error.  The most obvious difference from YYERROR is
+  that YYFAIL will automatically invoke yyerror to report the syntax
+  error so that you don't have to.  However, there are several other
+  subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
+  inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
+  used.  For a more detailed discussion, see:
+
+    http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
+
+  The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
+  deterministic parsers in C will continue to implement it.  However,
+  because YYFAIL is already flawed, it seems futile to try to make new
+  Bison features compatible with it.  Thus, during parser generation,
+  Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
+  rule action.  In a later release, YYFAIL will be disabled for
+  %error-verbose and `#define YYERROR_VERBOSE'.  Eventually, YYFAIL will
+  be removed altogether.
+
+  There exists at least one case where Bison 2.5's YYFAIL warning will
+  be a false positive.  Some projects add phony uses of YYFAIL and other
+  Bison-defined macros for the sole purpose of suppressing C
+  preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
+  To avoid Bison's future warning, such YYFAIL uses can be moved to the
+  epilogue (that is, after the second `%%') in the Bison input file.  In
+  this release (2.4.2), Bison already generates its own code to suppress
+  C preprocessor warnings for YYFAIL, so projects can remove their own
+  phony uses of YYFAIL if compatibility with Bison releases prior to
+  2.4.2 is not necessary.
+
+** Internationalization.
+
+  Fix a regression introduced in Bison 2.4: Under some circumstances,
+  message translations were not installed although supported by the
+  host system.
+

 * Changes in version 2.4.1 (2008-12-11):
 
 ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
 * Changes in version 2.4.1 (2008-12-11):
 
 ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc


@@ -1192,8 +1511,7 @@ End:
 
 -----
 
 
 -----
 

-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+Copyright (C) 1995-2011 Free Software Foundation, Inc.

 
 This file is part of Bison, the GNU Parser Generator.
 
 
 This file is part of Bison, the GNU Parser Generator.