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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/>.