X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/035aa4a0bbf1847843c48312d892f79599ba7d8a..3be03b13e5fd9cc9ed119f26e429e6ab1dd3568d:/NEWS diff --git a/NEWS b/NEWS index ec0a8dec..5ecabf59 100644 --- a/NEWS +++ b/NEWS @@ -1,25 +1,185 @@ Bison News ---------- -Changes in version 2.1a: +Changes in version 2.3+: + +* 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 a default %destructor and %printer: + + For example: + + %union { char *string; } + %token STRING1 + %token STRING2 + %type string1 + %type string2 + %destructor { free ($$); } %symbol-default + %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 + + guarantees that, when the parser discards any user-defined symbol, 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 + associating token numbers with token names. Removing the #define statements + helps to sanitize the global namespace during preprocessing, but POSIX Yacc + requires them. Bison still generates an enum for token names in all cases. + +* Handling of traditional Yacc prologue blocks is now more consistent but + potentially incompatible with previous releases of Bison. + + As before, you declare prologue blocks in your grammar file with the + `%{ ... %}' 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. + + 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 + latter case, Bison inserted it only into the code file. For parsers in C++, + the point of insertion was before any token definitions (which associate + token numbers with names). For parsers in C, the point of insertion was + after the token definitions. + + Now, Bison never inserts the pre-prologue into the header file. In the code + file, it always inserts it before the token definitions. + +* Bison now provides a more flexible alternative to the traditional Yacc + prologue blocks: %before-header, %start-header, %end-header, and + %after-header. + + For example, the following declaration order in the grammar file reflects the + order in which Bison will output these code blocks. However, you are free to + declare these code blocks in your grammar file in whatever order is most + convenient for you: + + %before-header { + /* Bison treats this block like a pre-prologue block: it inserts it into + * the code file before the contents of the header file. It does *not* + * insert it into the header file. This is a good place to put + * #include's that you want at the top of your code file. A common + * example is `#include "system.h"'. */ + } + %start-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is before any Bison-generated + * token, semantic type, location type, and class definitions. This is a + * good place to define %union dependencies, for example. */ + } + %union { + /* Unlike the traditional Yacc prologue blocks, the output order for the + * new %*-header blocks is not affected by their declaration position + * relative to any %union in the grammar file. */ + } + %end-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is after the Bison-generated + * definitions. This is a good place to declare or define public + * functions or data structures that depend on the Bison-generated + * definitions. */ + } + %after-header { + /* Bison treats this block like a post-prologue block: it inserts it into + * the code file after the contents of the header file. It does *not* + * insert it into the header file. This is a good place to declare or + * define internal functions or data structures that depend on the + * Bison-generated definitions. */ + } + + If you have multiple occurrences of any one of the above declarations, Bison + will concatenate the contents in declaration order. + +* 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. + +Changes in version 2.3, 2006-06-05: + +* GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING', + for compatibility with LALR(1) grammars. + +* It is now documented that any definition of YYSTYPE or YYLTYPE should + be to a type name that does not contain parentheses or brackets. + +Changes in version 2.2, 2006-05-19: + +* The distribution terms for all Bison-generated parsers now permit + using the parsers in nonfree programs. Previously, this permission + was granted only for Bison-generated LALR(1) parsers in C. + +* %name-prefix changes the namespace name in C++ outputs. + +* The C++ parsers export their token_type. + +* Bison now allows multiple %union declarations, and concatenates + their contents together. + +* New warning: unused values + Right-hand side symbols whose values are not used are reported, + if the symbols have destructors. For instance: + + exp: exp "?" exp ":" exp { $1 ? $1 : $3; } + | exp "+" exp + ; + + will trigger a warning about $$ and $5 in the first rule, and $3 in + the second ($1 is copied to $$ by the default rule). This example + most likely contains three errors, and could be rewritten as: + + exp: exp "?" exp ":" exp + { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); } + | exp "+" exp + { $$ = $1 ? $1 : $3; if ($1) free ($3); } + ; + + However, if the original actions were really intended, memory leaks + and all, the warnings can be suppressed by letting Bison believe the + values are used, e.g.: + + exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); } + | exp "+" exp { $$ = $1; (void) $3; } + ; + + If there are mid-rule actions, the warning is issued if no action + uses it. The following triggers no warning: $1 and $3 are used. + + exp: exp { push ($1); } '+' exp { push ($3); sum (); }; + + The warning is intended to help catching lost values and memory leaks. + If a value is ignored, its associated memory typically is not reclaimed. + +* %destructor vs. YYABORT, YYACCEPT, and YYERROR. + Destructors are now called when user code invokes YYABORT, YYACCEPT, + and YYERROR, for all objects on the stack, other than objects + corresponding to the right-hand side of the current rule. * %expect, %expect-rr Incorrect numbers of expected conflicts are now actual errors, instead of warnings. * GLR, YACC parsers. - The %parse-params are available in the %destructor's (and the - experimental %printer's) as per the documentation. + The %parse-params are available in the destructors (and the + experimental printers) as per the documentation. * Bison now warns if it finds a stray `$' or `@' in an action. * %require "VERSION" - To specify that the grammar file depends on features implemented in - Bison version VERSION or higher. + This specifies that the grammar file depends on features implemented + in Bison version VERSION or higher. * lalr1.cc: The token and value types are now class members. - The tokens where defined as free form enums and cpp macros. YYSTYPE - was defined as a free form union. Both are now class members: + The tokens were defined as free form enums and cpp macros. YYSTYPE + was defined as a free form union. They are now class members: tokens are enumerations of the `yy::parser::token' struct, and the semantic values have the `yy::parser::semantic_type' type. @@ -29,12 +189,14 @@ Changes in version 2.1a: for previous releases of Bison, and this one. If you wish to update, then make sure older version of Bison will - fail using `%require "2.1a"'. + fail using `%require "2.2"'. * DJGPP support added. - + Changes in version 2.1, 2005-09-16: +* The C++ lalr1.cc skeleton supports %lex-param. + * Bison-generated parsers now support the translation of diagnostics like "syntax error" into languages other than English. The default language is still English. For details, please see the new @@ -56,7 +218,7 @@ Changes in version 2.1, 2005-09-16: a syntax error associated with '%token NUM "number"' they might print 'syntax error, unexpected number' instead of 'syntax error, unexpected "number"'. - + Changes in version 2.0, 2004-12-25: * Possibly-incompatible changes @@ -99,8 +261,7 @@ Changes in version 2.0, 2004-12-25: This is a GNU extension. - The option `--report=lookahead' was changed to `--report=look-ahead'. - The old spelling still works, but is not documented and will be - removed. + [However, this was changed back after 2.3.] - Experimental %destructor support has been added to lalr1.cc. @@ -367,8 +528,8 @@ Changes in version 1.50, 2002-10-04: produces additional information: - itemset complete the core item sets with their closure - - lookahead [changed to `look-ahead' in 1.875e and later] - explicitly associate look-ahead tokens to items + - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back] + explicitly associate lookahead tokens to items - solved describe shift/reduce conflicts solving. Bison used to systematically output this information on top of @@ -651,8 +812,8 @@ End: ----- -Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 -Free Software Foundation, Inc. +Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, +2004, 2005, 2006 Free Software Foundation, Inc. This file is part of Bison, the GNU Compiler Compiler.