Bison News
----------
-Changes in version 2.3+:
+Changes in version 2.3a+ (????-??-??):
+
+* The -g and --graph options now output graphs in Graphviz DOT format,
+ not VCG format.
+
+* An experimental directive %language specifies the language of the
+ generated parser, which can be C (the default) or C++. This
+ directive affects the skeleton used, and the names of the generated
+ files if the grammar file's name ends in ".y".
+
+* The grammar file may now specify the name of the parser header file using
+ %defines. For example:
+
+ %defines "parser.h"
+
+* The `=' that used to be required in the following declarations is now
+ deprecated:
+
+ %file-prefix "parser"
+ %name-prefix "c_"
+ %output "parser.c"
+
+* Bison 2.3a provided a new set of directives as a more flexible alternative to
+ the traditional Yacc prologue blocks. Those have now been consolidated into
+ a single %code directive with an optional qualifier field, which identifies
+ the purpose of the code and thus the location(s) where Bison should generate
+ it:
+
+ 1. `%code {CODE}' replaces `%after-header {CODE}'
+ 2. `%code "requires" {CODE}' replaces `%start-header {CODE}'
+ 3. `%code "provides" {CODE}' replaces `%end-header {CODE}'
+ 4. `%code "top" {CODE}' replaces `%before-header {CODE}'
+
+ See the %code entries in `Appendix A Bison Symbols' in the Bison manual for a
+ summary of the new functionality. See the new section `Prologue
+ Alternatives' for a detailed discussion including the advantages of %code
+ over the traditional Yacc prologues.
+
+ The prologue alternatives are experimental. More user feedback will help to
+ determine whether they should become permanent features.
+
+* Revised warning: unset or unused mid-rule values
+
+ Since Bison 2.2, Bison has warned about mid-rule values that are set but not
+ used within any of the actions of the parent rule. For example, Bison warns
+ about unused $2 in:
+
+ exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
+
+ Now, Bison also warns about mid-rule values that are used but not set. For
+ example, Bison warns about unset $$ in the mid-rule action in:
+
+ exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
+
+ However, Bison now disables both of these warnings by default since they
+ sometimes prove to be false alarms in existing grammars employing the Yacc
+ constructs $0 or $-N (where N is some positive integer).
+
+ To enable these warnings, specify the flag `--warnings=midrule-values' or
+ `-W', which is a synonym for `--warnings=all'.
+
+* Bison now recognizes two separate kinds of default %destructor's and
+ %printer's:
+
+ 1. Place `<*>' in a %destructor/%printer symbol list to define a default
+ %destructor/%printer for all grammar symbols for which you have formally
+ declared semantic type tags.
+
+ 2. Place `<>' in a %destructor/%printer symbol list to define a default
+ %destructor/%printer for all grammar symbols without declared semantic
+ type tags.
+
+ Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
+ `<*>' and `<>' combined achieve the same effect with one exception: Bison no
+ longer applies any %destructor to a mid-rule value if that mid-rule value is
+ not actually ever referenced using either $$ or $n in a semantic action.
+
+ The default %destructor's and %printer's are experimental. More user
+ feedback will help to determine whether they should become permanent
+ features.
+
+ See the section `Freeing Discarded Symbols' in the Bison manual for further
+ details.
+
+Changes in version 2.3a, 2006-09-13:
* Instead of %union, you can define and use your own union type
YYSTYPE if your grammar contains at least one <type> tag.
also prints its line number to `stdout'. It performs only the second
`%destructor' in this case, so it invokes `free' only once.
+ [Although we failed to mention this here in the 2.3a release, the default
+ %destructor's and %printer's were experimental, and they were rewritten in
+ future versions.]
+
* Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
`--yacc', or `%yacc'), Bison no longer generates #define statements for
associating token numbers with token names. Removing the #define statements
If you have multiple occurrences of any one of the above declarations, Bison
will concatenate the contents in declaration order.
+ [Although we failed to mention this here in the 2.3a release, the prologue
+ alternatives were experimental, and they were rewritten in future versions.]
+
* The option `--report=look-ahead' has been changed to `--report=lookahead'.
The old spelling still works, but is not documented and may be removed
in a future release.
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