+ one may now declare
+
+ %param {arg1_type *arg1} {arg2_type *arg2}
+
+** Java skeleton improvements
+
+ The constants for token names were moved to the Lexer interface.
+ Also, it is possible to add code to the parser's constructors using
+ "%code init" and "%define init_throws".
+
+** Variable api.tokens.prefix
+
+ The variable api.tokens.prefix changes the way tokens are identified in
+ the generated files. This is especially useful to avoid collisions
+ with identifiers in the target language. For instance
+
+ %token FILE for ERROR
+ %define api.tokens.prefix "TOK_"
+ %%
+ start: FILE for ERROR;
+
+ will generate the definition of the symbols TOK_FILE, TOK_for, and
+ TOK_ERROR in the generated sources. In particular, the scanner must
+ use these prefixed token names, although the grammar itself still
+ uses the short names (as in the sample rule given above).
+
+** Variable api.namespace
+
+ The "namespace" variable is renamed "api.namespace". Backward
+ compatibility is ensured, but upgrading is recommended.
+
+** Variable parse.error
+
+ The variable error controls the verbosity of error messages. The
+ use of the %error-verbose directive is deprecated in favor of
+ %define parse.error "verbose".
+
+* Changes in version 2.5 (????-??-??):
+
+** Named References Support
+
+ 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) Support
+
+ 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'. See the documentation
+ for `%define lr.type' and `%define lr.default-reductions' in the
+ section `Bison Declaration Summary' in the Bison manual for the
+ details.
+
+ These features are experimental. More user feedback will help to
+ stabilize them.
+
+** Unrecognized %code qualifiers are now an error not a warning.
+
+** %define improvements.
+
+*** Unrecognized variables are now an error not a warning.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+*** 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 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
+
+** Symbol names.
+
+ Consistently with directives (such as %error-verbose) and variables
+ (e.g. push-pull), symbol names may include dashes in any position,
+ similarly to periods and underscores. This is GNU extension over
+ POSIX Yacc whose use is reported by -Wyacc, and rejected in Yacc
+ mode (--yacc).
+
+** 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.
+
+** 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 report an error instead.
+
+** Verbose error messages fixed for nonassociative tokens.
+
+ When %error-verbose is specified, syntax error messages produced by
+ the generated parser include the unexpected token as well as a list of
+ expected tokens. Previously, this list erroneously included tokens
+ that would actually induce a syntax error because conflicts for them
+ were resolved with %nonassoc. Such tokens are now properly omitted
+ from the list.
+
+* Changes in version 2.4.2 (????-??-??):
+
+** Detection of GNU M4 1.4.6 or newer during configure is improved.
+
+** %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.
+
+** 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:
+
+ %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.
+\f
+* 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"'.
+\f
+* 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.
+\f
+* 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.
+\f
+* 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.
+\f
+* 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.
+\f
+* 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.
+\f
+* 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.
+\f
+* 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.
+\f
+* Changes in version 1.32, 2002-01-23:
+
+** Fix Yacc output file names
+
+** Portability fixes
+
+** Italian, Dutch translations
+\f
+* 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'.
+\f
+* 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.
projects / bison.git / blobdiff