* 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:
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.
1. %code {CODE}
Other than semantic actions, this is probably the most common place you
- should write verbatim code for the parser implementation. For C/C++, it
- replaces the traditional Yacc prologue, `%{CODE%}', for most purposes.
- For Java, it inserts your CODE into the parser class. Compare with:
-
- - `%{CODE%}' appearing after the first `%union {CODE}' in a C/C++
- based 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.
+ 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. For C/C++, 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. For Java, this is the right place to write import
- directives. Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a C/C++
- based 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.
+ 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. For C/C++, this directive inserts your CODE
+ 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. For Java, it inserts your CODE into the
- parser java file after the parser class. Compare with:
+ Bison's required definitions. Compare with:
- `%end-header {CODE}', which only Bison 2.3a supported.
4. %code-top {CODE}
- Occasionally for C/C++ it is desirable to insert code near the top of
- the parser code file. For example:
+ 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>
}
- For Java, `%code-top {CODE}' is currently unused. Compare with:
+ Compare with:
- - `%{CODE%}' appearing before the first `%union {CODE}' in a C/C++
- based 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}'.
+ - `%{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:
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.
projects / bison.git / blobdiff