Code cleanup.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 1a98c191d4ff23407c4d3104d220759cc708f3b4..a4d9b45b5cd5336025101c336e74b347cc937e11 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,22 +3,202 @@ Bison News
 
 * Changes in version 2.5 (????-??-??):
 
 
 * Changes in version 2.5 (????-??-??):
 

-** %define can now be invoked via the command line.
+** Named References Support

 
 

-  Each of these bison command-line options
+  Historically, Yacc and Bison have supported positional references
+  ($n, $$) to allow access to symbol values from inside of semantic
+  actions code.

 
 

-    -D NAME=VALUE
-    --define=NAME=VALUE
+  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) Support
+
+  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,
+  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
+  significantly reduce the complexity of developing of a grammar.
+
+  Bison can now generate IELR(1) and canonical LR(1) parser tables in
+  place of its traditional LALR(1) parser tables, which remain the
+  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
+
+  The default reduction optimization in the parser tables can also be
+  adjusted using `%define lr.default-reductions'.  See the documentation
+  for `%define lr.type' and `%define lr.default-reductions' in the
+  section `Bison Declaration Summary' in the Bison manual for the
+  details.
+
+  These features are experimental.  More user feedback will help to
+  stabilize them.
+
+** Unrecognized %code qualifiers are now an error not a warning.
+
+** %define improvements.
+
+*** Unrecognized variables are now an error not a warning.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+*** Can now be invoked via the command line.
+
+  Each of these command-line options
+
+    -D NAME[=VALUE]
+    --define=NAME[=VALUE]
+
+    -F NAME[=VALUE]
+    --force-define=NAME[=VALUE]

 
   is equivalent to this grammar file declaration
 
 
   is equivalent to this grammar file declaration
 

-    %define NAME "VALUE"
+    %define NAME ["VALUE"]
+
+  except that the manner in which Bison processes multiple definitions
+  for the same NAME differs.  Most importantly, -F and --force-define
+  quietly override %define, but -D and --define do not.  For further
+  details, see the section "Bison Options" in the Bison manual.
+
+*** Variables renamed.
+
+  The following %define variables
+
+    api.push_pull
+    lr.keep_unreachable_states
+
+  have been renamed to
+
+    api.push-pull
+    lr.keep-unreachable-states
+
+  The old names are now deprecated but will be maintained indefinitely
+  for backward compatibility.
+
+*** Values no longer need to be quoted in grammar file.
+
+  If a %define value is an identifier, it no longer needs to be placed
+  within quotations marks.  For example,
+
+    %define api.push-pull "push"

 
 

-  for any NAME and VALUE.  Omitting `=VALUE' on the command line is
-  equivalent to omitting `"VALUE"' in the declaration.
+  can be rewritten as
+
+    %define api.push-pull push
+
+** Symbol names.
+
+  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).
+
+** 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
+  neither %yacc, %language, %skeleton, or equivalent command-line
+  options were specified).  This allowed actions such as
+
+    exp: exp "+" exp { $$ = $1 + $3 };
+
+  instead of
+
+    exp: exp "+" exp { $$ = $1 + $3; };
+
+  As a first step in removing this misfeature, Bison now issues a
+  warning when it appends a semicolon.  Moreover, in cases where Bison
+  cannot easily determine whether a semicolon is needed (for example, an
+  action ending with a cpp directive or a braced compound initializer),
+  it no longer appends one.  Thus, the C compiler might now complain
+  about a missing semicolon where it did not before.  Future releases of
+  Bison will cease to append semicolons entirely.
+
+** 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 report an error instead.
+
+** Verbose error messages fixed for nonassociative tokens.
+
+  When %error-verbose is specified, syntax error messages produced by
+  the generated parser include the unexpected token as well as a list of
+  expected tokens.  Previously, this list erroneously included tokens
+  that would actually induce a syntax error because conflicts for them
+  were resolved with %nonassoc.  Such tokens are now properly omitted
+  from the list.

 
 * Changes in version 2.4.2 (????-??-??):
 
 
 * Changes in version 2.4.2 (????-??-??):
 

+** 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.
+
+  A traditional Yacc prologue directive is written in the form:
+
+    %{CODE%}
+
+  To provide a more flexible alternative, Bison 2.3b introduced the
+  %code directive with the following forms for C/C++:
+
+    %code          {CODE}
+    %code requires {CODE}
+    %code provides {CODE}
+    %code top      {CODE}
+
+  These forms are now considered permanent features of Bison.  See the
+  %code entries in the section "Bison Declaration Summary" in the Bison
+  manual for a summary of their functionality.  See the section
+  "Prologue Alternatives" for a detailed discussion including the
+  advantages of %code over the traditional Yacc prologue directive.
+
+  Bison's Java feature as a whole including its current usage of %code
+  is still considered experimental.
+
+** 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