* m4/c-working.m4: New file.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 176ce6f27df09ec78e2954172852b64eeade8674..e982759c2a2724a709ec6d64b4866a6a32d40857 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,17 +3,20 @@ Bison News
 
 Changes in version 2.1a:
 
+* Bison now allows multiple %union declarations, and concatenates
+  their contents together.
+
 * New warning: unused values
   Typed right-hand side symbols whose value are not used are reported.
   For instance:
 
-     exp: exp "?" exp ":" exp { $$ = $1 ? $1 : $3; }
+     exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
        | exp "+" exp
        ;
 
-  will trigger a warning about $5 of the first rule, and $3 in the
-  second ($1 is copied to $$ by the default rule).  This example
-  most likely contains two errors, and should be rewritten as:
+  will trigger a warning about $$ 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 should be rewritten as:
 
      exp: exp "?" exp ":" exp { $$ = $1 ? $3 : $5; }
        | exp "+" exp         { $$ = $1 + $3; }
@@ -22,10 +25,21 @@ Changes in version 2.1a:
   However, if the original actions were really intended, the warnings
   can be suppressed by letting Bison believe the values are used, e.g.:
 
-     exp: exp "?" exp ":" exp { $$ = $1 ? $1 : $3; (void) $5; }
+     exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $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 (); };
+
+  Mid-rule actions that use $$ cause the corresponding value to be
+  set, therefore the following action must use it.  The following rule
+  triggers a warning about $2.
+
+     exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
+
   The warning is intended to help catching lost values and memory leaks.
   If a value is ignored, its associated memory typically is not reclaimed.
 
@@ -684,8 +698,8 @@ End:
 
 -----
 
-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
-Free Software Foundation, Inc.
+Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
+2004, 2005, 2006 Free Software Foundation, Inc.
 
 This file is part of Bison, the GNU Compiler Compiler.