X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/a501eca911c81bd7875633ff1d9734e1fb4a3fe3..d3b129885fc028cf5388841536ad9274af93d61a:/NEWS diff --git a/NEWS b/NEWS index 75e0284f..68fb66f0 100644 --- a/NEWS +++ b/NEWS @@ -6,78 +6,95 @@ Changes in version 2.3a+ (????-??-??): * The -g and --graph options now output graphs in Graphviz DOT format, not VCG format. -* 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. 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. - - `%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. - - `%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 - 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: - - - `%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: - - %code-top { - #define _GNU_SOURCE - #include - } - - For Java, `%code-top {CODE}' is currently unused. 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}'. - - `%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. - - Also see the new section `Prologue Alternatives' in the Bison manual. +* 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 directives is now + deprecated: + + %file-prefix "parser" + %name-prefix "c_" + %output "parser.c" + +* The quotes around NAME that used to be required in the following directive + are now deprecated: + + %define NAME "VALUE" + +* 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: +* Bison now supports generating Java parsers. Grammars written for + the Java language should include the `%language "Java"' directive. + * Instead of %union, you can define and use your own union type YYSTYPE if your grammar contains at least one tag. Your YYSTYPE need not be a macro; it can be a typedef. @@ -109,6 +126,10 @@ 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 @@ -179,6 +200,9 @@ Changes in version 2.3a, 2006-09-13: 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. @@ -893,7 +917,7 @@ End: ----- Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, -2004, 2005, 2006 Free Software Foundation, Inc. +2004, 2005, 2006, 2007 Free Software Foundation, Inc. This file is part of Bison, the GNU Compiler Compiler.