Bison News
----------
-Changes in version 2.3a+ (????-??-??):
+* Changes in version 2.5.1 (????-??-??):
+
+** Some portability problems in the test suite have been fixed.
+
+** Minor improvements have been made to the manual.
-* The quotes around NAME that used to be required in the following directive
+* Changes in version 2.5 (2011-05-14):
+
+** Grammar symbol names can now contain non-initial dashes:
+
+ Consistently with directives (such as %error-verbose) and with
+ %define variables (e.g. push-pull), grammar symbol names may contain
+ dashes in any position except the beginning. This is a GNU
+ extension over POSIX Yacc. Thus, use of this extension is reported
+ by -Wyacc and rejected in Yacc mode (--yacc).
+
+** Named references:
+
+ Historically, Yacc and Bison have supported positional references
+ ($n, $$) to allow access to symbol values from inside of semantic
+ actions code.
+
+ Starting from this version, Bison can also accept named references.
+ When no ambiguity is possible, original symbol names may be used
+ as named references:
+
+ if_stmt : "if" cond_expr "then" then_stmt ';'
+ { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
+
+ In the more common case, explicit names may be declared:
+
+ stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
+ { $res = mk_if_stmt($cond, $then, $else); }
+
+ Location information is also accessible using @name syntax. When
+ accessing symbol names containing dots or dashes, explicit bracketing
+ ($[sym.1]) must be used.
+
+ These features are experimental in this version. More user feedback
+ will help to stabilize them.
+
+** IELR(1) and canonical LR(1):
+
+ IELR(1) is a minimal LR(1) parser table generation algorithm. That
+ is, given any context-free grammar, IELR(1) generates parser tables
+ with the full language-recognition power of canonical LR(1) but with
+ nearly the same number of parser states as LALR(1). This reduction
+ in parser states is often an order of magnitude. More importantly,
+ because canonical LR(1)'s extra parser states may contain duplicate
+ conflicts in the case of non-LR(1) grammars, the number of conflicts
+ for IELR(1) is often an order of magnitude less as well. This can
+ significantly reduce the complexity of developing of a grammar.
+
+ Bison can now generate IELR(1) and canonical LR(1) parser tables in
+ place of its traditional LALR(1) parser tables, which remain the
+ default. You can specify the type of parser tables in the grammar
+ file with these directives:
+
+ %define lr.type lalr
+ %define lr.type ielr
+ %define lr.type canonical-lr
+
+ The default-reduction optimization in the parser tables can also be
+ adjusted using `%define lr.default-reductions'. For details on both
+ of these features, see the new section `Tuning LR' in the Bison
+ manual.
+
+ These features are experimental. More user feedback will help to
+ stabilize them.
+
+** LAC (Lookahead Correction) for syntax error handling:
+
+ Canonical LR, IELR, and LALR can suffer from a couple of problems
+ upon encountering a syntax error. First, the parser might perform
+ additional parser stack reductions before discovering the syntax
+ error. Such reductions can perform user semantic actions that are
+ unexpected because they are based on an invalid token, and they
+ cause error recovery to begin in a different syntactic context than
+ the one in which the invalid token was encountered. Second, when
+ verbose error messages are enabled (with %error-verbose or the
+ obsolete `#define YYERROR_VERBOSE'), the expected token list in the
+ syntax error message can both contain invalid tokens and omit valid
+ tokens.
+
+ The culprits for the above problems are %nonassoc, default
+ reductions in inconsistent states, and parser state merging. Thus,
+ IELR and LALR suffer the most. Canonical LR can suffer only if
+ %nonassoc is used or if default reductions are enabled for
+ inconsistent states.
+
+ LAC is a new mechanism within the parsing algorithm that solves
+ these problems for canonical LR, IELR, and LALR without sacrificing
+ %nonassoc, default reductions, or state merging. When LAC is in
+ use, canonical LR and IELR behave almost exactly the same for both
+ syntactically acceptable and syntactically unacceptable input.
+ While LALR still does not support the full language-recognition
+ power of canonical LR and IELR, LAC at least enables LALR's syntax
+ error handling to correctly reflect LALR's language-recognition
+ power.
+
+ Currently, LAC is only supported for deterministic parsers in C.
+ You can enable LAC with the following directive:
+
+ %define parse.lac full
+
+ See the new section `LAC' in the Bison manual for additional
+ details including a few caveats.
+
+ LAC is an experimental feature. More user feedback will help to
+ stabilize it.
+
+** %define improvements:
+
+*** Can now be invoked via the command line:
+
+ Each of these command-line options
+
+ -D NAME[=VALUE]
+ --define=NAME[=VALUE]
+
+ -F NAME[=VALUE]
+ --force-define=NAME[=VALUE]
+
+ is equivalent to this grammar file declaration
+
+ %define NAME ["VALUE"]
+
+ except that the manner in which Bison processes multiple definitions
+ for the same NAME differs. Most importantly, -F and --force-define
+ quietly override %define, but -D and --define do not. For further
+ details, see the section `Bison Options' in the Bison manual.
+
+*** Variables renamed:
+
+ The following %define variables
+
+ api.push_pull
+ lr.keep_unreachable_states
+
+ have been renamed to
+
+ api.push-pull
+ lr.keep-unreachable-states
+
+ The old names are now deprecated but will be maintained indefinitely
+ for backward compatibility.
+
+*** Values no longer need to be quoted in the grammar file:
+
+ If a %define value is an identifier, it no longer needs to be placed
+ within quotations marks. For example,
+
+ %define api.push-pull "push"
+
+ can be rewritten as
+
+ %define api.push-pull push
+
+*** Unrecognized variables are now errors not warnings.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+** Unrecognized %code qualifiers are now errors not warnings.
+
+** Character literals not of length one:
+
+ Previously, Bison quietly converted all character literals to length
+ one. For example, without warning, Bison interpreted the operators in
+ the following grammar to be the same token:
+
+ exp: exp '++'
+ | exp '+' exp
+ ;
+
+ Bison now warns when a character literal is not of length one. In
+ some future release, Bison will start reporting an error instead.
+
+** Destructor calls fixed for lookaheads altered in semantic actions:
+
+ Previously for deterministic parsers in C, if a user semantic action
+ altered yychar, the parser in some cases used the old yychar value to
+ determine which destructor to call for the lookahead upon a syntax
+ error or upon parser return. This bug has been fixed.
+
+** C++ parsers use YYRHSLOC:
+
+ Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
+ macro and use it in the default YYLLOC_DEFAULT. You are encouraged
+ to use it. If, for instance, your location structure has `first'
+ and `last' members, instead of
+
+ # define YYLLOC_DEFAULT(Current, Rhs, N) \
+ do \
+ if (N) \
+ { \
+ (Current).first = (Rhs)[1].location.first; \
+ (Current).last = (Rhs)[N].location.last; \
+ } \
+ else \
+ { \
+ (Current).first = (Current).last = (Rhs)[0].location.last; \
+ } \
+ while (false)
+
+ use:
+
+ # define YYLLOC_DEFAULT(Current, Rhs, N) \
+ do \
+ if (N) \
+ { \
+ (Current).first = YYRHSLOC (Rhs, 1).first; \
+ (Current).last = YYRHSLOC (Rhs, N).last; \
+ } \
+ else \
+ { \
+ (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
+ } \
+ while (false)
+
+** YYLLOC_DEFAULT in C++:
+
+ The default implementation of YYLLOC_DEFAULT used to be issued in
+ the header file. It is now output in the implementation file, after
+ the user %code sections so that its #ifndef guard does not try to
+ override the user's YYLLOC_DEFAULT if provided.
+
+** YYFAIL now produces warnings and Java parsers no longer implement it:
+
+ YYFAIL has existed for many years as an undocumented feature of
+ deterministic parsers in C generated by Bison. More recently, it was
+ a documented feature of Bison's experimental Java parsers. As
+ promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
+ semantic action now produces a deprecation warning, and Java parsers
+ no longer implement YYFAIL at all. For further details, including a
+ discussion of how to suppress C preprocessor warnings about YYFAIL
+ being unused, see the Bison 2.4.2 NEWS entry.
+
+** Temporary hack for adding a semicolon to the user action:
+
+ Previously, Bison appended a semicolon to every user action for
+ reductions when the output language defaulted to C (specifically, when
+ neither %yacc, %language, %skeleton, or equivalent command-line
+ options were specified). This allowed actions such as
+
+ exp: exp "+" exp { $$ = $1 + $3 };
+
+ instead of
+
+ exp: exp "+" exp { $$ = $1 + $3; };
+
+ As a first step in removing this misfeature, Bison now issues a
+ warning when it appends a semicolon. Moreover, in cases where Bison
+ cannot easily determine whether a semicolon is needed (for example, an
+ action ending with a cpp directive or a braced compound initializer),
+ it no longer appends one. Thus, the C compiler might now complain
+ about a missing semicolon where it did not before. Future releases of
+ Bison will cease to append semicolons entirely.
+
+** Verbose syntax error message fixes:
+
+ When %error-verbose or the obsolete `#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 a more complete fix requires LAC, described above:
+
+*** 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
+ invalid tokens 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. Bison's new LAC implementation,
+ described above, eliminates this problem and the need for
+ canonical LR. However, LAC is still experimental and is disabled
+ by default.
+
+** Java skeleton fixes:
+
+*** A location handling bug has been fixed.
+
+*** The top element of each of the value stack and location stack is now
+ cleared when popped so that it can be garbage collected.
+
+*** Parser traces now print the top element of the stack.
+
+** -W/--warnings fixes:
+
+*** Bison now properly recognizes the `no-' versions of categories:
+
+ For example, given the following command line, Bison now enables all
+ warnings except warnings for incompatibilities with POSIX Yacc:
+
+ bison -Wall,no-yacc gram.y
+
+*** Bison now treats S/R and R/R conflicts like other warnings:
+
+ Previously, conflict reports were independent of Bison's normal
+ warning system. Now, Bison recognizes the warning categories
+ `conflicts-sr' and `conflicts-rr'. This change has important
+ consequences for the -W and --warnings command-line options. For
+ example:
+
+ bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
+ bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
+ bison -Wnone gram.y # no conflicts are reported
+ bison -Werror gram.y # any conflict is an error
+
+ However, as before, if the %expect or %expect-rr directive is
+ specified, an unexpected number of conflicts is an error, and an
+ expected number of conflicts is not reported, so -W and --warning
+ then have no effect on the conflict report.
+
+*** The `none' category no longer disables a preceding `error':
+
+ For example, for the following command line, Bison now reports
+ errors instead of warnings for incompatibilities with POSIX Yacc:
+
+ bison -Werror,none,yacc gram.y
+
+*** The `none' category now disables all Bison warnings:
+
+ Previously, the `none' category disabled only Bison warnings for
+ which there existed a specific -W/--warning category. However,
+ given the following command line, Bison is now guaranteed to
+ suppress all warnings:
+
+ bison -Wnone gram.y
+
+** Precedence directives can now assign token number 0:
+
+ Since Bison 2.3b, which restored the ability of precedence
+ directives to assign token numbers, doing so for token number 0 has
+ produced an assertion failure. For example:
+
+ %left END 0
+
+ This bug has been fixed.
+
+* 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.
+
+** Failures in the test suite for GCC 4.5 have been fixed.
+
+** Failures in the test suite for some versions of Sun Studio C++ have
+ been fixed.
+
+** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
+ warnings about undefined %prec identifiers will not be converted to
+ 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
+ in the test suite on some versions of at least Solaris, AIX, HP-UX,
+ RHEL4, and Tru64 have been addressed. As a result, fatal Bison
+ errors should no longer cause M4 to report a broken pipe on the
+ affected platforms.
+
+** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
+
+ POSIX specifies that an error be reported for any identifier that does
+ not appear on the LHS of a grammar rule and that is not defined by
+ %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
+ error report for the case when an identifier appears only after a
+ %prec directive. It is now restored. However, for backward
+ compatibility with recent Bison releases, it is only a warning for
+ now. In Bison 2.5 and later, it will return to being an error.
+ [Between the 2.4.2 and 2.4.3 releases, it was decided that this
+ warning will not be converted to an error in Bison 2.5.]
+
+** Detection of GNU M4 1.4.6 or newer during configure is improved.
+
+** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
+ YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
+ avoided.
+
+** %code is now a permanent feature.
+
+ A traditional Yacc prologue directive is written in the form:
+
+ %{CODE%}
+
+ To provide a more flexible alternative, Bison 2.3b introduced the
+ %code directive with the following forms for C/C++:
+
+ %code {CODE}
+ %code requires {CODE}
+ %code provides {CODE}
+ %code top {CODE}
+
+ These forms are now considered permanent features of Bison. See the
+ %code entries in the section "Bison Declaration Summary" in the Bison
+ manual for a summary of their functionality. See the section
+ "Prologue Alternatives" for a detailed discussion including the
+ advantages of %code over the traditional Yacc prologue directive.
+
+ Bison's Java feature as a whole including its current usage of %code
+ is still considered experimental.
+
+** YYFAIL is deprecated and will eventually be removed.
+
+ YYFAIL has existed for many years as an undocumented feature of
+ deterministic parsers in C generated by Bison. Previously, it was
+ documented for Bison's experimental Java parsers. YYFAIL is no longer
+ documented for Java parsers and is formally deprecated in both cases.
+ Users are strongly encouraged to migrate to YYERROR, which is
+ specified by POSIX.
+
+ Like YYERROR, you can invoke YYFAIL from a semantic action in order to
+ induce a syntax error. The most obvious difference from YYERROR is
+ that YYFAIL will automatically invoke yyerror to report the syntax
+ error so that you don't have to. However, there are several other
+ subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
+ inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
+ used. For a more detailed discussion, see:
+
+ http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
+
+ The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
+ deterministic parsers in C will continue to implement it. However,
+ because YYFAIL is already flawed, it seems futile to try to make new
+ Bison features compatible with it. Thus, during parser generation,
+ Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
+ rule action. In a later release, YYFAIL will be disabled for
+ %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will
+ be removed altogether.
+
+ There exists at least one case where Bison 2.5's YYFAIL warning will
+ be a false positive. Some projects add phony uses of YYFAIL and other
+ Bison-defined macros for the sole purpose of suppressing C
+ preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
+ To avoid Bison's future warning, such YYFAIL uses can be moved to the
+ epilogue (that is, after the second `%%') in the Bison input file. In
+ this release (2.4.2), Bison already generates its own code to suppress
+ C preprocessor warnings for YYFAIL, so projects can remove their own
+ phony uses of YYFAIL if compatibility with Bison releases prior to
+ 2.4.2 is not necessary.
+
+** Internationalization.
+
+ Fix a regression introduced in Bison 2.4: Under some circumstances,
+ message translations were not installed although supported by the
+ host system.
+
+* Changes in version 2.4.1 (2008-12-11):
+
+** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
+ declarations have been fixed.
+
+** Temporary hack for adding a semicolon to the user action.
+
+ Bison used to prepend a trailing semicolon at the end of the user
+ action for reductions. This allowed actions such as
+
+ exp: exp "+" exp { $$ = $1 + $3 };
+
+ instead of
+
+ exp: exp "+" exp { $$ = $1 + $3; };
+
+ Some grammars still depend on this `feature'. Bison 2.4.1 restores
+ the previous behavior in the case of C output (specifically, when
+ neither %language or %skeleton or equivalent command-line options
+ are used) to leave more time for grammars depending on the old
+ behavior to be adjusted. Future releases of Bison will disable this
+ feature.
+
+** A few minor improvements to the Bison manual.
+
+* Changes in version 2.4 (2008-11-02):
+
+** %language is an experimental feature.
+
+ We first introduced this feature in test release 2.3b as a cleaner
+ alternative to %skeleton. Since then, we have discussed the possibility of
+ modifying its effect on Bison's output file names. Thus, in this release,
+ we consider %language to be an experimental feature that will likely evolve
+ in future releases.
+
+** Forward compatibility with GNU M4 has been improved.
+
+** Several bugs in the C++ skeleton and the experimental Java skeleton have been
+ fixed.
+
+* Changes in version 2.3b (2008-05-27):
+
+** The quotes around NAME that used to be required in the following directive
are now deprecated:
%define NAME "VALUE"
-* The directive `%pure-parser' is now deprecated in favor of:
+** The directive `%pure-parser' is now deprecated in favor of:
%define api.pure
which has the same effect except that Bison is more careful to warn about
unreasonable usage in the latter case.
-* Push Parsing
+** Push Parsing
Bison can now generate an LALR(1) parser in C with a push interface. That
- is, instead of invoking yyparse, which pulls tokens from `yylex', you can
+ is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
push one token at a time to the parser using `yypush_parse', which will
return to the caller after processing each token. By default, the push
interface is disabled. Either of the following directives will enable it:
See the new section `A Push Parser' in the Bison manual for details.
-* The -g and --graph options now output graphs in Graphviz DOT format,
- not VCG format.
+ The current push parsing interface is experimental and may evolve. More user
+ feedback will help to stabilize it.
+
+** The -g and --graph options now output graphs in Graphviz DOT format,
+ not VCG format. Like --graph, -g now also takes an optional FILE argument
+ and thus cannot be bundled with other short options.
+
+** Java
+
+ Bison can now generate an LALR(1) parser in Java. The skeleton is
+ `data/lalr1.java'. Consider using the new %language directive instead of
+ %skeleton to select it.
+
+ See the new section `Java Parsers' in the Bison manual for details.
-* An experimental directive %language specifies the language of the
- generated parser, which can be C (the default) or C++. This
- directive affects the skeleton used, and the names of the generated
- files if the grammar file's name ends in ".y".
+ The current Java interface is experimental and may evolve. More user
+ feedback will help to stabilize it.
-* The grammar file may now specify the name of the parser header file using
+** %language
+
+ This new directive specifies the programming language of the generated
+ parser, which can be C (the default), C++, or Java. Besides the skeleton
+ that Bison uses, the directive affects the names of the generated files if
+ the grammar file's name ends in ".y".
+
+** XML Automaton Report
+
+ Bison can now generate an XML report of the LALR(1) automaton using the new
+ `--xml' option. The current XML schema is experimental and may evolve. More
+ user feedback will help to stabilize it.
+
+** The grammar file may now specify the name of the parser header file using
%defines. For example:
%defines "parser.h"
-* Unreachable State Removal
+** When reporting useless rules, useless nonterminals, and unused terminals,
+ Bison now employs the terms "useless in grammar" instead of "useless",
+ "useless in parser" instead of "never reduced", and "unused in grammar"
+ instead of "unused".
+
+** Unreachable State Removal
Previously, Bison sometimes generated parser tables containing unreachable
states. A state can become unreachable during conflict resolution if Bison
directives in existing grammar files.
3. For any rule used only in such states, Bison now reports the rule as
- "never reduced because of conflicts".
+ "useless in parser due to conflicts".
This feature can be disabled with the following directive:
See the %define entry in the `Bison Declaration Summary' in the Bison manual
for further discussion.
-* Lookahead Set Correction in the `.output' Report
-
+** Lookahead Set Correction in the `.output' Report
+
When instructed to generate a `.output' file including lookahead sets
(using `--report=lookahead', for example), Bison now prints each reduction's
lookahead set only next to the associated state's one item that (1) is
bug affected only the `.output' file and not the generated parser source
code.
-* The `=' that used to be required in the following directives is now
+** --report-file=FILE is a new option to override the default `.output' file
+ name.
+
+** The `=' that used to be required in the following directives is now
deprecated:
%file-prefix "parser"
%name-prefix "c_"
%output "parser.c"
-* An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
+** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
Bison 2.3a provided a new set of directives as a more flexible alternative to
the traditional Yacc prologue blocks. Those have now been consolidated into
The prologue alternatives are experimental. More user feedback will help to
determine whether they should become permanent features.
-* Revised warning: unset or unused mid-rule values
+** Revised warning: unset or unused mid-rule values
Since Bison 2.2, Bison has warned about mid-rule values that are set but not
used within any of the actions of the parent rule. For example, Bison warns
sometimes prove to be false alarms in existing grammars employing the Yacc
constructs $0 or $-N (where N is some positive integer).
- To enable these warnings, specify the flag `--warnings=midrule-values' or
+ To enable these warnings, specify the option `--warnings=midrule-values' or
`-W', which is a synonym for `--warnings=all'.
-* Default %destructor or %printer with `<*>' or `<>'
+** Default %destructor or %printer with `<*>' or `<>'
Bison now recognizes two separate kinds of default %destructor's and
%printer's:
See the section `Freeing Discarded Symbols' in the Bison manual for further
details.
-Changes in version 2.3a, 2006-09-13:
+** %left, %right, and %nonassoc can now declare token numbers. This is required
+ by POSIX. However, see the end of section `Operator Precedence' in the Bison
+ manual for a caveat concerning the treatment of literal strings.
+
+** The nonfunctional --no-parser, -n, and %no-parser options have been
+ completely removed from Bison.
+
+* Changes in version 2.3a, 2006-09-13:
-* Instead of %union, you can define and use your own union type
+** Instead of %union, you can define and use your own union type
YYSTYPE if your grammar contains at least one <type> 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.
+** 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:
+** You may now declare per-type and default %destructor's and %printer's:
For example:
%destructor's and %printer's were experimental, and they were rewritten in
future versions.]
-* Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
+** 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
+** 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
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
+** Bison now provides a more flexible alternative to the traditional Yacc
prologue blocks: %before-header, %start-header, %end-header, and
%after-header.
[Although we failed to mention this here in the 2.3a release, the prologue
alternatives were experimental, and they were rewritten in future versions.]
-* The option `--report=look-ahead' has been changed to `--report=lookahead'.
+** 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:
+* Changes in version 2.3, 2006-06-05:
-* GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
+** 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
+** 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:
+* Changes in version 2.2, 2006-05-19:
-* The distribution terms for all Bison-generated parsers now permit
+** 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.
+** %name-prefix changes the namespace name in C++ outputs.
-* The C++ parsers export their token_type.
+** The C++ parsers export their token_type.
-* Bison now allows multiple %union declarations, and concatenates
+** Bison now allows multiple %union declarations, and concatenates
their contents together.
-* New warning: unused values
+** New warning: unused values
Right-hand side symbols whose values are not used are reported,
if the symbols have destructors. For instance:
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.
+** %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
+** %expect, %expect-rr
Incorrect numbers of expected conflicts are now actual errors,
instead of warnings.
-* GLR, YACC parsers.
+** 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.
+** Bison now warns if it finds a stray `$' or `@' in an action.
-* %require "VERSION"
+** %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.
+** 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
If you wish to update, then make sure older version of Bison will
fail using `%require "2.2"'.
-* DJGPP support added.
+** DJGPP support added.
\f
-Changes in version 2.1, 2005-09-16:
+* Changes in version 2.1, 2005-09-16:
-* The C++ lalr1.cc skeleton supports %lex-param.
+** The C++ lalr1.cc skeleton supports %lex-param.
-* Bison-generated parsers now support the translation of diagnostics like
+** 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
+** 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
+** 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
+** 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"'.
\f
-Changes in version 2.0, 2004-12-25:
+* Changes in version 2.0, 2004-12-25:
-* Possibly-incompatible changes
+** Possibly-incompatible changes
- Bison-generated parsers no longer default to using the alloca function
(when available) to extend the parser stack, due to widespread
- NUL bytes are no longer allowed in Bison string literals, unfortunately.
-* New features
+** New features
- GLR grammars now support locations.
- New configure option --disable-yacc, to disable installation of the
yacc command and -ly library introduced in 1.875 for POSIX conformance.
-* Bug fixes
+** Bug fixes
- For now, %expect-count violations are now just warnings, not errors.
This is for compatibility with Bison 1.75 and earlier (when there are
- Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
\f
-Changes in version 1.875, 2003-01-01:
+* Changes in version 1.875, 2003-01-01:
-* The documentation license has been upgraded to version 1.2
+** The documentation license has been upgraded to version 1.2
of the GNU Free Documentation License.
-* syntax error processing
+** syntax error processing
- In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
locations too. This fixes bugs in error-location computation.
- #defining yyerror to steal internal variables is discouraged.
It is not guaranteed to work forever.
-* POSIX conformance
+** POSIX conformance
- Semicolons are once again optional at the end of grammar rules.
This reverts to the behavior of Bison 1.33 and earlier, and improves
using typedef instead of defining it as a macro.
For consistency, YYLTYPE is also declared instead of defined.
-* Other compatibility issues
+** Other compatibility issues
- %union directives can now have a tag before the `{', e.g., the
directive `%union foo {...}' now generates the C code
typedefs or tags; they are no longer documented and are planned to be
withdrawn in a future release.
-* GLR parser notes
+** GLR parser notes
- GLR and inline
Users of Bison have to decide how they handle the portability of the
- `parsing stack overflow...' -> `parser stack overflow'
GLR parsers now report `parser stack overflow' as per the Bison manual.
-* Bison now warns if it detects conflicting outputs to the same file,
+** Bison now warns if it detects conflicting outputs to the same file,
e.g., it generates a warning for `bison -d -o foo.h foo.y' since
that command outputs both code and header to foo.h.
-* #line in output files
+** #line in output files
- --no-line works properly.
-* Bison can no longer be built by a K&R C compiler; it requires C89 or
+** Bison can no longer be built by a K&R C compiler; it requires C89 or
later to be built. This change originally took place a few versions
ago, but nobody noticed until we recently asked someone to try
building Bison with a K&R C compiler.
\f
-Changes in version 1.75, 2002-10-14:
+* Changes in version 1.75, 2002-10-14:
-* Bison should now work on 64-bit hosts.
+** Bison should now work on 64-bit hosts.
-* Indonesian translation thanks to Tedi Heriyanto.
+** Indonesian translation thanks to Tedi Heriyanto.
-* GLR parsers
+** GLR parsers
Fix spurious parse errors.
-* Pure parsers
+** Pure parsers
Some people redefine yyerror to steal yyparse' private variables.
Reenable this trick until an official feature replaces it.
-* Type Clashes
+** Type Clashes
In agreement with POSIX and with other Yaccs, leaving a default
action is valid when $$ is untyped, and $1 typed:
typed: ... untyped;
-* Values of mid-rule actions
+** Values of mid-rule actions
The following code:
foo: { ... } { $$ = $1; } ...
was incorrectly rejected: $1 is defined in the second mid-rule
action, and is equal to the $$ of the first mid-rule action.
\f
-Changes in version 1.50, 2002-10-04:
+* Changes in version 1.50, 2002-10-04:
-* GLR parsing
+** GLR parsing
The declaration
%glr-parser
causes Bison to produce a Generalized LR (GLR) parser, capable of handling
Unfortunately Bison 1.50 does not work properly on 64-bit hosts
like the Alpha, so please stick to 32-bit hosts for now.
-* Output Directory
+** Output Directory
When not in Yacc compatibility mode, when the output file was not
specified, running `bison foo/bar.y' created `foo/bar.c'. It
now creates `bar.c'.
-* Undefined token
+** Undefined token
The undefined token was systematically mapped to 2 which prevented
the use of 2 by the user. This is no longer the case.
-* Unknown token numbers
+** Unknown token numbers
If yylex returned an out of range value, yyparse could die. This is
no longer the case.
-* Error token
+** Error token
According to POSIX, the error token must be 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.
-* Verbose error messages
+** Verbose error messages
They no longer report `..., expecting error or...' for states where
error recovery is possible.
-* End token
+** End token
Defaults to `$end' instead of `$'.
-* Error recovery now conforms to documentation and to POSIX
+** 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
Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
<http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
-* Traces
+** Traces
Popped tokens and nonterminals are now reported.
-* Larger grammars
+** Larger grammars
Larger grammars are now supported (larger token numbers, larger grammar
size (= sum of the LHS and RHS lengths), larger LALR tables).
Formerly, many of these numbers ran afoul of 16-bit limits;
now these limits are 32 bits on most hosts.
-* Explicit initial rule
+** 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
+** 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
+** Useless rules, useless nonterminals
They are now reported, as a warning, with their locations.
-* Rules never reduced
+** Rules never reduced
Rules that can never be reduced because of conflicts are now
reported.
-* Incorrect `Token not used'
+** Incorrect `Token not used'
On a grammar such as
%token useless 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
+** Revert the C++ namespace changes introduced in 1.31
as they caused too many portability hassles.
-* Default locations
+** 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 @$.
-* Token end-of-file
+** Token end-of-file
The token end of file may be specified by the user, in which case,
the user symbol is used in the reports, the graphs, and the verbose
error messages instead of `$end', which remains being the default.
or
%token MYEOF 0 "end of file"
-* Semantic parser
+** Semantic parser
This old option, which has been broken for ages, is removed.
-* New translations
+** New translations
Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
Croatian, thanks to Denis Lackovic.
-* Incorrect token definitions
+** Incorrect token definitions
When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
-* Token definitions as enums
+** 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 lets debuggers display names instead of integers.
-* Reports
+** Reports
In addition to --verbose, bison supports --report=THINGS, which
produces additional information:
- itemset
Bison used to systematically output this information on top of
the report. Solved conflicts are now attached to their states.
-* Type clashes
+** 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:
This is fixed.
-* GNU M4 is now required when using Bison.
+** GNU M4 is now required when using Bison.
\f
-Changes in version 1.35, 2002-03-25:
+* Changes in version 1.35, 2002-03-25:
-* C Skeleton
+** 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.
This kludge also addresses some C++ problems when the stack was
extended.
\f
-Changes in version 1.34, 2002-03-12:
+* Changes in version 1.34, 2002-03-12:
-* File name clashes are detected
+** 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
+** 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
+** Revert the C++ namespace changes introduced in 1.31, as they caused too
many portability hassles.
-* DJGPP support added.
+** DJGPP support added.
-* Fix test suite portability problems.
+** Fix test suite portability problems.
\f
-Changes in version 1.33, 2002-02-07:
+* Changes in version 1.33, 2002-02-07:
-* Fix C++ issues
+** Fix C++ issues
Groff could not be compiled for the definition of size_t was lacking
under some conditions.
-* Catch invalid @n
+** Catch invalid @n
As is done with $n.
\f
-Changes in version 1.32, 2002-01-23:
+* Changes in version 1.32, 2002-01-23:
-* Fix Yacc output file names
+** Fix Yacc output file names
-* Portability fixes
+** Portability fixes
-* Italian, Dutch translations
+** Italian, Dutch translations
\f
-Changes in version 1.31, 2002-01-14:
+* Changes in version 1.31, 2002-01-14:
-* Many Bug Fixes
+** Many Bug Fixes
-* GNU Gettext and %expect
+** 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
+** 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.
-* yyparse now returns 2 if memory is exhausted; formerly it dumped core.
+** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
-* When the generated parser lacks debugging code, YYDEBUG is now 0
+** When the generated parser lacks debugging code, YYDEBUG is now 0
(as POSIX requires) instead of being undefined.
-* User Actions
+** 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
+** 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
+** Reduced Grammars
Fixed bugs when reporting useless nonterminals.
-* 64 bit hosts
+** 64 bit hosts
The parsers work properly on 64 bit hosts.
-* Error messages
+** Error messages
Some calls to strerror resulted in scrambled or missing error messages.
-* %expect
+** %expect
When the number of shift/reduce conflicts is correct, don't issue
any warning.
-* The verbose report includes the rule line numbers.
+** The verbose report includes the rule line numbers.
-* Rule line numbers are fixed in traces.
+** Rule line numbers are fixed in traces.
-* Swedish translation
+** Swedish translation
-* Parse errors
+** 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.
+** 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.
+** Fixed verbose output file.
Some newlines were missing.
Some conflicts in state descriptions were missing.
-* Fixed conflict report.
+** Fixed conflict report.
Option -v was needed to get the result.
-* %expect
+** %expect
Was not used.
Mismatches are errors, not warnings.
-* Fixed incorrect processing of some invalid input.
+** Fixed incorrect processing of some invalid input.
-* Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
+** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
-* Fixed some typos in the documentation.
+** Fixed some typos in the documentation.
-* %token MY_EOF 0 is supported.
+** %token MY_EOF 0 is supported.
Before, MY_EOF was silently renumbered as 257.
-* doc/refcard.tex is updated.
+** doc/refcard.tex is updated.
-* %output, %file-prefix, %name-prefix.
+** %output, %file-prefix, %name-prefix.
New.
-* --output
+** --output
New, aliasing `--output-file'.
\f
-Changes in version 1.30, 2001-10-26:
+* Changes in version 1.30, 2001-10-26:
-* `--defines' and `--graph' have now an optional argument which is the
+** `--defines' and `--graph' have now an optional 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
+** `%source_extension' and `%header_extension' are removed, failed
experiment.
-* Portability fixes.
+** Portability fixes.
\f
-Changes in version 1.29, 2001-09-07:
+* Changes in version 1.29, 2001-09-07:
-* The output file does not define const, as this caused problems when used
+** 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'.
+** Added `-g' and `--graph'.
-* The Bison manual is now distributed under the terms of the GNU FDL.
+** The Bison manual is now distributed under the terms of the GNU FDL.
-* The input and the output files has automatically a similar extension.
+** The input and the output files has automatically a similar extension.
-* Russian translation added.
+** Russian translation added.
-* NLS support updated; should hopefully be less troublesome.
+** NLS support updated; should hopefully be less troublesome.
-* Added the old Bison reference card.
+** Added the old Bison reference card.
-* Added `--locations' and `%locations'.
+** Added `--locations' and `%locations'.
-* Added `-S' and `--skeleton'.
+** Added `-S' and `--skeleton'.
-* `%raw', `-r', `--raw' is disabled.
+** `%raw', `-r', `--raw' is disabled.
-* Special characters are escaped when output. This solves the problems
+** Special characters are escaped when output. This solves the problems
of the #line lines with path names including backslashes.
-* New directives.
+** New directives.
`%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
`%debug', `%source_extension' and `%header_extension'.
-* @$
+** @$
Automatic location tracking.
\f
-Changes in version 1.28, 1999-07-06:
+* Changes in version 1.28, 1999-07-06:
-* Should compile better now with K&R compilers.
+** Should compile better now with K&R compilers.
-* Added NLS.
+** Added NLS.
-* Fixed a problem with escaping the double quote character.
+** Fixed a problem with escaping the double quote character.
-* There is now a FAQ.
+** There is now a FAQ.
\f
-Changes in version 1.27:
+* Changes in version 1.27:
-* The make rule which prevented bison.simple from being created on
+** The make rule which prevented bison.simple from being created on
some systems has been fixed.
\f
-Changes in version 1.26:
+* Changes in version 1.26:
-* Bison now uses automake.
+** Bison now uses automake.
-* New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
+** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
-* Token numbers now start at 257 as previously documented, not 258.
+** Token numbers now start at 257 as previously documented, not 258.
-* Bison honors the TMPDIR environment variable.
+** Bison honors the TMPDIR environment variable.
-* A couple of buffer overruns have been fixed.
+** A couple of buffer overruns have been fixed.
-* Problems when closing files should now be reported.
+** Problems when closing files should now be reported.
-* Generated parsers should now work even on operating systems which do
+** Generated parsers should now work even on operating systems which do
not provide alloca().
\f
-Changes in version 1.25, 1995-10-16:
+* Changes in version 1.25, 1995-10-16:
-* Errors in the input grammar are not fatal; Bison keeps reading
+** 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
+** 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
+** 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
+** 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
+** 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 --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.
\f
-Changes in version 1.23:
+* 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
Line numbers in output file corrected.
\f
-Changes in version 1.22:
+* Changes in version 1.22:
--help option added.
\f
-Changes in version 1.20:
+* Changes in version 1.20:
Output file does not redefine const for C++.
-----
-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+Copyright (C) 1995-2011 Free Software Foundation, Inc.
-This file is part of Bison, the GNU Compiler Compiler.
+This file is part of Bison, the GNU Parser Generator.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
projects / bison.git / blobdiff