* 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:
%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
See the section `Freeing Discarded Symbols' in the Bison manual for further
details.
-* The Yacc prologue alternatives from Bison 2.3a have been rewritten as the
- following directives:
-
- 1. %code {CODE}
-
- Other than semantic actions, this is probably the most common place you
- should write verbatim code for the parser implementation. It replaces
- the traditional Yacc prologue, `%{CODE%}', for most purposes. Compare
- with:
-
- - `%{CODE%}' appearing after the first `%union {CODE}' in a grammar
- file. While Bison will continue to support `%{CODE%}' for backward
- compatibility, `%code {CODE}' is cleaner as its functionality does
- not depend on its position in the grammar file relative to any
- `%union {CODE}'. Specifically, `%code {CODE}' always inserts your
- CODE into the parser code file after the usual contents of the
- parser header file.
- - `%after-header {CODE}', which only Bison 2.3a supported.
-
- 2. %requires {CODE}
-
- This is the right place to write dependency code for externally exposed
- definitions required by Bison. Such exposed definitions are those
- usually appearing in the parser header file. Thus, this is the right
- place to define types referenced in `%union {CODE}' directives, and it
- is the right place to override Bison's default YYSTYPE and YYLTYPE
- definitions. Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
- file. Unlike `%{CODE%}', `%requires {CODE}' inserts your CODE both
- into the parser code file and into the parser header file since
- Bison's required definitions should depend on it in both places.
- - `%start-header {CODE}', which only Bison 2.3a supported.
-
- 3. %provides {CODE}
-
- This is the right place to write additional definitions you would like
- Bison to expose externally. That is, this directive inserts your CODE
- both into the parser header file and into the parser code file after
- Bison's required definitions. Compare with:
-
- - `%end-header {CODE}', which only Bison 2.3a supported.
-
- 4. %code-top {CODE}
-
- Occasionally it is desirable to insert code near the top of the parser
- code file. For example:
-
- %code-top {
- #define _GNU_SOURCE
- #include <stdio.h>
- }
-
- Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
- file. `%code-top {CODE}' is cleaner as its functionality does not
- depend on its position in the grammar file relative to any
- `%union {CODE}'.
- - `%before-header {CODE}', which only Bison 2.3a supported.
-
- If you have multiple occurrences of any one of the above four directives,
- Bison will concatenate the contents in the order they appear in the grammar
- file.
-
- The prologue alternatives are experimental. More user feedback will help to
- determine whether they should become permanent features.
-
- Also see the new section `Prologue Alternatives' in the Bison manual.
-
Changes in version 2.3a, 2006-09-13:
* Instead of %union, you can define and use your own union type
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