+* 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 ($3); sum (); };
+
+ The warning is intended to help catching lost values and memory leaks.
+ If a value is ignored, its associated memory typically is not reclaimed.
+
+* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
+ Destructors are now called when user code invokes YYABORT, YYACCEPT,
+ and YYERROR, for all objects on the stack, other than objects
+ corresponding to the right-hand side of the current rule.
+
+* %expect, %expect-rr
+ Incorrect numbers of expected conflicts are now actual errors,
+ instead of warnings.
+
+* GLR, YACC parsers.
+ The %parse-params are available in the destructors (and the
+ experimental printers) as per the documentation.
+
+* Bison now warns if it finds a stray `$' or `@' in an action.
+
+* %require "VERSION"
+ 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 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.
+
+ If you do not want or can update to this scheme, the directive
+ `%define "global_tokens_and_yystype" "1"' triggers the global
+ definition of tokens and YYSTYPE. This change is suitable both
+ 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"'.
+
+* 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
+ Internationalization section of the Bison manual. Software
+ distributors should also see the new PACKAGING file. Thanks to
+ Bruno Haible for this new feature.
+
+* Wording in the Bison-generated parsers has been changed slightly to
+ simplify translation. In particular, the message "memory exhausted"
+ has replaced "parser stack overflow", as the old message was not
+ always accurate for modern Bison-generated parsers.
+
+* Destructors are now called when the parser aborts, for all symbols left
+ behind on the stack. Also, the start symbol is now destroyed after a
+ successful parse. In both cases, the behavior was formerly inconsistent.
+
+* When generating verbose diagnostics, Bison-generated parsers no longer
+ quote the literal strings associated with tokens. For example, for
+ 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
+
+ - Bison-generated parsers no longer default to using the alloca function
+ (when available) to extend the parser stack, due to widespread
+ problems in unchecked stack-overflow detection. You can "#define
+ YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
+ the manual to determine safe values for YYMAXDEPTH in that case.
+
+ - Error token location.
+ During error recovery, the location of the syntax error is updated
+ to cover the whole sequence covered by the error token: it includes
+ the shifted symbols thrown away during the first part of the error
+ recovery, and the lookahead rejected during the second part.
+
+ - Semicolon changes:
+ . Stray semicolons are no longer allowed at the start of a grammar.
+ . Semicolons are now required after in-grammar declarations.
+
+ - Unescaped newlines are no longer allowed in character constants or
+ string literals. They were never portable, and GCC 3.4.0 has
+ dropped support for them. Better diagnostics are now generated if
+ forget a closing quote.
+
+ - NUL bytes are no longer allowed in Bison string literals, unfortunately.
+
+* New features
+
+ - GLR grammars now support locations.
+
+ - New directive: %initial-action.
+ This directive allows the user to run arbitrary code (including
+ initializing @$) from yyparse before parsing starts.
+
+ - A new directive "%expect-rr N" specifies the expected number of
+ reduce/reduce conflicts in GLR parsers.
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