use of the %error-verbose directive is deprecated in favor of
%define parse.error "verbose".
+** Semantic predicates
+
+ The new, experimental, semantic-predicate feature allows actions of
+ the form %?{ BOOLEAN-EXPRESSION }, which cause syntax errors (as for
+ YYERROR) if the expression evaluates to 0, and are evaluated immediately
+ in GLR parsers, rather than being deferred. The result is that they
+ allow the programmer to prune possible parses based on the values of
+ runtime expressions.
+
* Changes in version 2.5 (????-??-??):
** Named References Support
Bison now warns when a character literal is not of length one. In
some future release, Bison will report an error instead.
-** Verbose error messages fixed for nonassociative tokens.
-
- When %error-verbose is specified, syntax error messages produced by
- the generated parser include the unexpected token as well as a list of
- expected tokens. Previously, this list erroneously included tokens
- that would actually induce a syntax error because conflicts for them
- were resolved with %nonassoc. Such tokens are now properly omitted
- from the list.
+** Verbose syntax error message fixes:
+
+ When %error-verbose or `#define YYERROR_VERBOSE' is specified, syntax
+ error messages produced by the generated parser include the unexpected
+ token as well as a list of expected tokens. The effect of %nonassoc
+ on these verbose messages has been corrected in two ways, but
+ additional fixes are still being implemented:
+
+*** When %nonassoc is used, there can exist parser states that accept no
+ tokens, and so the parser does not always require a lookahead token
+ in order to detect a syntax error. Because no unexpected token or
+ expected tokens can then be reported, the verbose syntax error
+ message described above is suppressed, and the parser instead
+ reports the simpler message, "syntax error". Previously, this
+ suppression was sometimes erroneously triggered by %nonassoc when a
+ lookahead was actually required. Now verbose messages are
+ suppressed only when all previous lookaheads have already been
+ shifted or discarded.
+
+*** Previously, the list of expected tokens erroneously included tokens
+ that would actually induce a syntax error because conflicts for them
+ were resolved with %nonassoc in the current parser state. Such
+ tokens are now properly omitted from the list.
+
+*** Expected token lists are still often wrong due to state merging
+ (from LALR or IELR) and default reductions, which can both add and
+ subtract valid tokens. Canonical LR almost completely fixes this
+ problem by eliminating state merging and default reductions.
+ However, there is one minor problem left even when using canonical
+ LR and even after the fixes above. That is, if the resolution of a
+ conflict with %nonassoc appears in a later parser state than the one
+ at which some syntax error is discovered, the conflicted token is
+ still erroneously included in the expected token list. We are
+ currently working on a fix to eliminate this problem and to
+ eliminate the need for canonical LR.
** Destructor calls fixed for lookaheads altered in semantic actions.
the user %code sections so that its #ifndef guard does not try to
override the user's YYLLOC_DEFAULT if provided.
-* Changes in version 2.4.3 (????-??-??):
+* Changes in version 2.4.3 (2010-08-05):
+
+** Bison now obeys -Werror and --warnings=error for warnings about
+ grammar rules that are useless in the parser due to conflicts.
** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
been fixed.
errors in Bison 2.5. They will remain warnings, which should be
sufficient for POSIX while avoiding backward compatibility issues.
+** Minor documentation fixes.
+
* Changes in version 2.4.2 (2010-03-20):
** Some portability problems that resulted in failures and livelocks
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