Bison News ---------- Changes in version 1.49b: * GLR parsing The declaration %glr-parser causes Bison to produce a Generalized LR (GLR) parser, capable of handling almost any context-free grammar, ambiguous or not. The new declarations %dprec and %merge on grammar rules allow parse-time resolution of ambiguities. Contributed by Paul Hilfinger. * Output Directory When not in Yacc compatibility mode, when the output file was not specified, runnning `bison foo/bar.y' created `foo/bar.c'. It now creates `bar.c'. * Undefined token The undefined token was systematically mapped to 2 which prevented the use of 2 from the user. This is no longer the case. * Unknown token numbers If yylex returned a code out of range, yyparse could die. This is no longer the case. * Error token According to POSIX, the error token should be numbered as 256. Bison extends this requirement by making it a preference: *if* the user specified that one of her tokens is numbered 256, then error will be mapped onto another number. * Error recovery now conforms to documentation and to POSIX When a Bison-generated parser encounters a syntax error, it now pops the stack until it finds a state that allows shifting the error token. Formerly, it popped the stack until it found a state that allowed some non-error action other than a default reduction on the error token. The new behavior has long been the documented behavior, and has long been required by POSIX. For more details, please see . * Traces Popped tokens and nonterminals are now reported. * Large grammars Large grammars are now supported (large token numbers, large grammar size (= sum of the LHS and RHS lengths), large LALR tables). * Explicit initial rule Bison used to play hacks with the initial rule, which the user does not write. It is now explicit, and visible in the reports and graphs as rule 0. * Useless rules Before, Bison reported the useless rules, but, although not used, included them in the parsers. They are now actually removed. * Useless rules, useless nonterminals They are now reported, as a warning, with their locations. * Rules never reduced Rules that can never be reduced because of conflicts are now reported. * Incorrect `Token not used' On a grammar such as %token useless useful %% exp: '0' %prec useful; where a token was used to set the precedence of the last rule, bison reported both `useful' and `useless' as useless tokens. * Revert the C++ namespace changes introduced in 1.31 as they caused too many portability hassles. * Default locations By an accident of design, the default computation of @$ was performed after another default computation was performed: @$ = @1. The latter is now removed: YYLLOC_DEFAULT is fully responsible of the computation of @$. * Token end-of-file The token end of file may be specified by the user, in which case, the user symbol is used in the reports, the graphs, and the verbose error messages instead of `$', which remains being the defaults. For instance %token YYEOF 0 or %token YYEOF 0 "end of file" * Semantic parser This old option, which has been broken for ages, is removed. * New translation Croatian, thanks to Denis Lackovic. * Incorrect token definitions When fed with `%token 'a' "A"', Bison used to output `#define 'a' 65'. * Token definitions as enums Tokens are output both as the traditional #define's, and, provided the compiler supports ANSI C or is a C++ compiler, as enums. This helps debuggers producing symbols instead of values. * Reports In addition to --verbose, bison supports --report=THINGS, which produces additional information: - itemset complete the core item sets with their closure - lookahead explicitly associate lookaheads to items - solved describe shift/reduce conflicts solving. Bison used to systematically output this information on top of the report. Solved conflicts are now attached to their states. * Type clashes Previous versions don't complain when there is a type clash on the default action if the rule has a mid-rule action, such as in: %type bar %% bar: '0' {} '0'; This is fixed. Changes in version 1.35, 2002-03-25: * C Skeleton Some projects use Bison's C parser with C++ compilers, and define YYSTYPE as a class. The recent adjustment of C parsers for data alignment and 64 bit architectures made this impossible. Because for the time being no real solution for C++ parser generation exists, kludges were implemented in the parser to maintain this use. In the future, when Bison has C++ parsers, this kludge will be disabled. This kludge also addresses some C++ problems when the stack was extended. Changes in version 1.34, 2002-03-12: * File name clashes are detected $ bison foo.y -d -o foo.x fatal error: header and parser would both be named `foo.x' * A missing `;' at the end of a rule triggers a warning In accordance with POSIX, and in agreement with other Yacc implementations, Bison will mandate this semicolon in the near future. This eases the implementation of a Bison parser of Bison grammars by making this grammar LALR(1) instead of LR(2). To facilitate the transition, this release introduces a warning. * Revert the C++ namespace changes introduced in 1.31, as they caused too many portability hassles. * DJGPP support added. * Fix test suite portability problems. Changes in version 1.33, 2002-02-07: * Fix C++ issues Groff could not be compiled for the definition of size_t was lacking under some conditions. * Catch invalid @n As is done with $n. Changes in version 1.32, 2002-01-23: * Fix Yacc output file names * Portability fixes * Italian, Dutch translations Changes in version 1.31, 2002-01-14: * Many Bug Fixes * GNU Gettext and %expect GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that Bison dies on incorrect %expectations, we fear there will be too many bug reports for Gettext, so _for the time being_, %expect does not trigger an error when the input file is named `plural.y'. * Use of alloca in parsers If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use malloc exclusively. Since 1.29, but was not NEWS'ed. alloca is used only when compiled with GCC, to avoid portability problems as on AIX. * When the generated parser lacks debugging code, YYDEBUG is now 0 (as POSIX requires) instead of being undefined. * User Actions Bison has always permitted actions such as { $$ = $1 }: it adds the ending semicolon. Now if in Yacc compatibility mode, the semicolon is no longer output: one has to write { $$ = $1; }. * Better C++ compliance The output parsers try to respect C++ namespaces. [This turned out to be a failed experiment, and it was reverted later.] * Reduced Grammars Fixed bugs when reporting useless nonterminals. * 64 bit hosts The parsers work properly on 64 bit hosts. * Error messages Some calls to strerror resulted in scrambled or missing error messages. * %expect When the number of shift/reduce conflicts is correct, don't issue any warning. * The verbose report includes the rule line numbers. * Rule line numbers are fixed in traces. * Swedish translation * Parse errors Verbose parse error messages from the parsers are better looking. Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'('' Now: parse error: unexpected '/', expecting "number" or '-' or '(' * Fixed parser memory leaks. When the generated parser was using malloc to extend its stacks, the previous allocations were not freed. * Fixed verbose output file. Some newlines were missing. Some conflicts in state descriptions were missing. * Fixed conflict report. Option -v was needed to get the result. * %expect Was not used. Mismatches are errors, not warnings. * Fixed incorrect processing of some invalid input. * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H. * Fixed some typos in the documentation. * %token MY_EOF 0 is supported. Before, MY_EOF was silently renumbered as 257. * doc/refcard.tex is updated. * %output, %file-prefix, %name-prefix. New. * --output New, aliasing `--output-file'. Changes in version 1.30, 2001-10-26: * `--defines' and `--graph' have now an optionnal argument which is the output file name. `-d' and `-g' do not change, they do not take any argument. * `%source_extension' and `%header_extension' are removed, failed experiment. * Portability fixes. Changes in version 1.29, 2001-09-07: * The output file does not define const, as this caused problems when used with common autoconfiguration schemes. If you still use ancient compilers that lack const, compile with the equivalent of the C compiler option `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this. * Added `-g' and `--graph'. * The Bison manual is now distributed under the terms of the GNU FDL. * The input and the output files has automatically a similar extension. * Russian translation added. * NLS support updated; should hopefully be less troublesome. * Added the old Bison reference card. * Added `--locations' and `%locations'. * Added `-S' and `--skeleton'. * `%raw', `-r', `--raw' is disabled. * Special characters are escaped when output. This solves the problems of the #line lines with path names including backslashes. * New directives. `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose', `%debug', `%source_extension' and `%header_extension'. * @$ Automatic location tracking. Changes in version 1.28, 1999-07-06: * Should compile better now with K&R compilers. * Added NLS. * Fixed a problem with escaping the double quote character. * There is now a FAQ. Changes in version 1.27: * The make rule which prevented bison.simple from being created on some systems has been fixed. Changes in version 1.26: * Bison now uses automake. * New mailing lists: and . * Token numbers now start at 257 as previously documented, not 258. * Bison honors the TMPDIR environment variable. * A couple of buffer overruns have been fixed. * Problems when closing files should now be reported. * Generated parsers should now work even on operating systems which do not provide alloca(). Changes in version 1.25, 1995-10-16: * Errors in the input grammar are not fatal; Bison keeps reading the grammar file, and reports all the errors found in it. * Tokens can now be specified as multiple-character strings: for example, you could use "<=" for a token which looks like <=, instead of chosing a name like LESSEQ. * The %token_table declaration says to write a table of tokens (names and numbers) into the parser file. The yylex function can use this table to recognize multiple-character string tokens, or for other purposes. * The %no_lines declaration says not to generate any #line preprocessor directives in the parser file. * The %raw declaration says to use internal Bison token numbers, not Yacc-compatible token numbers, when token names are defined as macros. * The --no-parser option produces the parser tables without including the parser engine; a project can now use its own parser engine. The actions go into a separate file called NAME.act, in the form of a switch statement body. Changes in version 1.23: The user can define YYPARSE_PARAM as the name of an argument to be passed into yyparse. The argument should have type void *. It should actually point to an object. Grammar actions can access the variable by casting it to the proper pointer type. Line numbers in output file corrected. Changes in version 1.22: --help option added. Changes in version 1.20: Output file does not redefine const for C++. Local Variables: mode: outline End: ----- Copyright (C) 2001, 2002 Free Software Foundation, Inc. This file is part of GNU Autoconf. GNU Autoconf is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. 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