X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/34f98f46ee16dd3719d19e002dc27b2665a2514f..31283fc38a9168a3d191f1db5ff3a76bc3c4ccbf:/NEWS diff --git a/NEWS b/NEWS index dd36e633..c3fe6d03 100644 --- a/NEWS +++ b/NEWS @@ -1,7 +1,132 @@ 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. + +* 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. + + 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. 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. + +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 tag. + Your YYSTYPE need not be a macro; it can be a typedef. + This change is for compatibility with other Yacc implementations, + and is required by POSIX. + +* Locations columns and lines start at 1. + In accordance with the GNU Coding Standards and Emacs. + +* You may now declare per-type and default %destructor's and %printer's: + + For example: + + %union { char *string; } + %token STRING1 + %token STRING2 + %type string1 + %type string2 + %union { char character; } + %token CHR + %type chr + %destructor { free ($$); } %symbol-default + %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 + %destructor { } + + guarantees that, when the parser discards any user-defined symbol that has a + semantic type tag other than `', it passes its semantic value to + `free'. However, when the parser discards a `STRING1' or a `string1', it + also prints its line number to `stdout'. It performs only the second + `%destructor' in this case, so it invokes `free' only once. * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y', `--yacc', or `%yacc'), Bison no longer generates #define statements for @@ -16,7 +141,7 @@ Changes in version 2.3+: `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all prologue blocks that you've declared before the first %union. To generate the post-prologue, Bison concatenates all prologue blocks that you've - declared after the first %union. + declared after the first %union. Previous releases of Bison inserted the pre-prologue into both the header file and the code file in all cases except for LALR(1) parsers in C. In the