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Bison News
----------
* 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:
%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
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
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:
%define api.push_pull "push" // Just push; does not require yylex.
%define api.push_pull "both" // Push and pull; requires yylex.
See the new section `A Push Parser' in the Bison manual for details.
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.
The current Java interface is experimental and may evolve. More user
feedback will help to stabilize it.
** %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"
** 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
disables a shift action leading to it from a predecessor state. Bison now:
1. Removes unreachable states.
2. Does not report any conflicts that appeared in unreachable states.
WARNING: As a result, you may need to update %expect and %expect-rr
directives in existing grammar files.
3. For any rule used only in such states, Bison now reports the rule as
"useless in parser due to conflicts".
This feature can be disabled with the following directive:
%define lr.keep_unreachable_states
See the %define entry in the `Bison Declaration Summary' in the Bison manual
for further discussion.
** 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
associated with the same rule as the reduction and (2) has its dot at the end
of its RHS. Previously, Bison also erroneously printed the lookahead set
next to all of the state's other items associated with the same rule. This
bug affected only the `.output' file and not the generated parser source
code.
** --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}'
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
a single %code directive with an optional qualifier field, which identifies
the purpose of the code and thus the location(s) where Bison should generate
it:
1. `%code {CODE}' replaces `%after-header {CODE}'
2. `%code requires {CODE}' replaces `%start-header {CODE}'
3. `%code provides {CODE}' replaces `%end-header {CODE}'
4. `%code top {CODE}' replaces `%before-header {CODE}'
See the %code entries in section `Bison Declaration Summary' in the Bison
manual for a summary of the new functionality. See the new section `Prologue
Alternatives' for a detailed discussion including the advantages of %code
over the traditional Yacc prologues.
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
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
about unused $2 in:
exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
Now, Bison also warns about mid-rule values that are used but not set. For
example, Bison warns about unset $$ in the mid-rule action in:
exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
However, Bison now disables both of these warnings by default since they
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 option `--warnings=midrule-values' or
`-W', which is a synonym for `--warnings=all'.
** Default %destructor or %printer with `<*>' or `<>'
Bison now recognizes two separate kinds of default %destructor's and
%printer's:
1. Place `<*>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols for which you have formally
declared semantic type tags.
2. Place `<>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols without declared semantic
type tags.
Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
`<*>' and `<>' combined achieve the same effect with one exception: Bison no
longer applies any %destructor to a mid-rule value if that mid-rule value is
not actually ever referenced using either $$ or $n in a semantic action.
The default %destructor's and %printer's are experimental. More user
feedback will help to determine whether they should become permanent
features.
See the section `Freeing Discarded Symbols' in the Bison manual for further
details.
** %left, %right, and %nonassoc can now declare token numbers. This is required
by POSIX. However, see the end of section `Operator Precedence' in the Bison
manual for a caveat concerning the treatment of literal strings.
** The nonfunctional --no-parser, -n, and %no-parser options have been
completely removed from Bison.
* Changes in version 2.3a, 2006-09-13:
** Instead of %union, you can define and use your own union type
YYSTYPE if your grammar contains at least one <type> tag.
Your YYSTYPE need not be a macro; it can be a typedef.
This change is for compatibility with other Yacc implementations,
and is required by POSIX.
** Locations columns and lines start at 1.
In accordance with the GNU Coding Standards and Emacs.
** You may now declare per-type and default %destructor's and %printer's:
For example:
%union { char *string; }
%token <string> STRING1
%token <string> STRING2
%type <string> string1
%type <string> string2
%union { char character; }
%token <character> CHR
%type <character> chr
%destructor { free ($$); } %symbol-default
%destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
%destructor { } <character>
guarantees that, when the parser discards any user-defined symbol that has a
semantic type tag other than `<character>', 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.
[Although we failed to mention this here in the 2.3a release, the default
%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',
`--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.
[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 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 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 "2.2"'.
** 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
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.
- %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
This is a GNU extension.
- The option `--report=lookahead' was changed to `--report=look-ahead'.
[However, this was changed back after 2.3.]
- Experimental %destructor support has been added to lalr1.cc.
- New configure option --disable-yacc, to disable installation of the
yacc command and -ly library introduced in 1.875 for POSIX conformance.
** 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
reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
are too many or too few shift/reduce conflicts). However, in future
versions of Bison we plan to improve the %expect machinery so that
these violations will become errors again.
- Within Bison itself, numbers (e.g., goto numbers) are no longer
arbitrarily limited to 16-bit counts.
- Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
* Changes in version 1.875, 2003-01-01:
** The documentation license has been upgraded to version 1.2
of the GNU Free Documentation License.
** syntax error processing
- In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
locations too. This fixes bugs in error-location computation.
- %destructor
It is now possible to reclaim the memory associated to symbols
discarded during error recovery. This feature is still experimental.
- %error-verbose
This new directive is preferred over YYERROR_VERBOSE.
- #defining yyerror to steal internal variables is discouraged.
It is not guaranteed to work forever.
** 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
compatibility with Yacc.
- `parse error' -> `syntax error'
Bison now uniformly uses the term `syntax error'; formerly, the code
and manual sometimes used the term `parse error' instead. POSIX
requires `syntax error' in diagnostics, and it was thought better to
be consistent.
- The documentation now emphasizes that yylex and yyerror must be
declared before use. C99 requires this.
- Bison now parses C99 lexical constructs like UCNs and
backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
- File names are properly escaped in C output. E.g., foo\bar.y is
output as "foo\\bar.y".
- Yacc command and library now available
The Bison distribution now installs a `yacc' command, as POSIX requires.
Also, Bison now installs a small library liby.a containing
implementations of Yacc-compatible yyerror and main functions.
This library is normally not useful, but POSIX requires it.
- Type clashes now generate warnings, not errors.
- If the user does not define YYSTYPE as a macro, Bison now declares it
using typedef instead of defining it as a macro.
For consistency, YYLTYPE is also declared instead of defined.
** Other compatibility issues
- %union directives can now have a tag before the `{', e.g., the
directive `%union foo {...}' now generates the C code
`typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
This is for compatibility with both Yacc and Bison 1.35.
- `;' is output before the terminating `}' of an action, for
compatibility with Bison 1.35.
- Bison now uses a Yacc-style format for conflict reports, e.g.,
`conflicts: 2 shift/reduce, 1 reduce/reduce'.
- `yystype' and `yyltype' are now obsolescent macros instead of being
typedefs or tags; they are no longer documented and are planned to be
withdrawn in a future release.
** GLR parser notes
- GLR and inline
Users of Bison have to decide how they handle the portability of the
C keyword `inline'.
- `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,
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
- --no-line works properly.
** 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.
* Changes in version 1.75, 2002-10-14:
** Bison should now work on 64-bit hosts.
** Indonesian translation thanks to Tedi Heriyanto.
** GLR parsers
Fix spurious parse errors.
** Pure parsers
Some people redefine yyerror to steal yyparse' private variables.
Reenable this trick until an official feature replaces it.
** Type Clashes
In agreement with POSIX and with other Yaccs, leaving a default
action is valid when $$ is untyped, and $1 typed:
untyped: ... typed;
but the converse remains an error:
typed: ... untyped;
** 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.
* Changes in version 1.50, 2002-10-04:
** 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.
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
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
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
If yylex returned an out of range value, yyparse could die. This is
no longer the case.
** 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
They no longer report `..., expecting error or...' for states where
error recovery is possible.
** End token
Defaults to `$end' instead of `$'.
** 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
Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
<http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
** Traces
Popped tokens and nonterminals are now reported.
** 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
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 @$.
** Token end-of-file
The token end of file may be specified by the user, in which case,
the user symbol is used in the reports, the graphs, and the verbose
error messages instead of `$end', which remains being the default.
For instance
%token MYEOF 0
or
%token MYEOF 0 "end of file"
** Semantic parser
This old option, which has been broken for ages, is removed.
** New translations
Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
Croatian, thanks to Denis Lackovic.
** Incorrect token definitions
When given `%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 lets debuggers display names instead of integers.
** Reports
In addition to --verbose, bison supports --report=THINGS, which
produces additional information:
- itemset
complete the core item sets with their closure
- 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
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 <foo> bar
%%
bar: '0' {} '0';
This is fixed.
** GNU M4 is now required when using Bison.
* 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.
** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
** 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 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
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: <bug-bison@gnu.org> and <help-bison@gnu.org>.
** 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) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
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
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
Copyright 2K16 - 2K18 Indonesian Hacker Rulez
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