X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/6deb44470e47bb02f0ca3ea630408d013e128710..4586c8cdb7c018de9cd16fdd0faa8ff749e69876:/NEWS diff --git a/NEWS b/NEWS index 8fbadf4e..2a0592a1 100644 --- a/NEWS +++ b/NEWS @@ -1,78 +1,1365 @@ Bison News ---------- -Changes in version 1.28a: +* Changes in version ?.? (????-??-??): -* Russian translation added. +** Additional yylex/yyparse arguments -* NLS support updated; should hopefully be less troublesome. + The new directive %param declare additional argument to both yylex + and yyparse. The %lex-param, %parse-param, and %param directive + support one or more arguments. Instead of -* Added the old Bison reference card. + %lex-param {arg1_type *arg1} + %lex-param {arg2_type *arg2} + %parse-param {arg1_type *arg1} + %parse-param {arg2_type *arg2} -* Added `--locations' and `%locations'. + one may now declare -* New directives. - `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose', and - `%debug'. + %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). + +** YYFAIL now produces warnings and Java parsers no longer implement it. + + YYFAIL has existed for many years as an undocumented feature of + deterministic parsers in C generated by Bison. More recently, it was + a documented feature of Bison's experimental Java parsers. As + promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a + semantic action now produces a deprecation warning, and Java parsers + no longer implement YYFAIL at all. For further details, including a + discussion of how to suppress C preprocessor warnings about YYFAIL + being unused, see the Bison 2.4.2 NEWS entry. + +** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately. + + As promised in Bison 2.4.2's NEWS entry, it is now an error if a token + that appears after a %prec directive is not defined by %token, %left, + %right, or %nonassoc. This is required by POSIX. + +** 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. + +** Destructor calls fixed for lookaheads altered in semantic actions. + + Previously for deterministic parsers in C, if a user semantic action + altered yychar, the parser in some cases used the old yychar value to + determine which destructor to call for the lookahead upon a syntax + error or upon parser return. This bug has been fixed. + +* Changes in version 2.4.3 (????-??-??): + +** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have + been fixed. + +** Failures in the test suite for GCC 4.5 have been fixed. + +* Changes in version 2.4.2 (2010-03-20): + +** Some portability problems that resulted in failures and livelocks + in the test suite on some versions of at least Solaris, AIX, HP-UX, + RHEL4, and Tru64 have been addressed. As a result, fatal Bison + errors should no longer cause M4 to report a broken pipe on the + affected platforms. + +** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately. + + POSIX specifies that an error be reported for any identifier that does + not appear on the LHS of a grammar rule and that is not defined by + %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this + error report for the case when an identifier appears only after a + %prec directive. It is now restored. However, for backward + compatibility with recent Bison releases, it is only a warning for + now. In Bison 2.5 and later, it will return to being an error. + +** Detection of GNU M4 1.4.6 or newer during configure is improved. + +** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS, + YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now + avoided. + +** %code is now a permanent feature. + + A traditional Yacc prologue directive is written in the form: + + %{CODE%} + + To provide a more flexible alternative, Bison 2.3b introduced the + %code directive with the following forms for C/C++: + + %code {CODE} + %code requires {CODE} + %code provides {CODE} + %code top {CODE} + + These forms are now considered permanent features of Bison. See the + %code entries in the section "Bison Declaration Summary" in the Bison + manual for a summary of their functionality. See the section + "Prologue Alternatives" for a detailed discussion including the + advantages of %code over the traditional Yacc prologue directive. + + Bison's Java feature as a whole including its current usage of %code + is still considered experimental. + +** YYFAIL is deprecated and will eventually be removed. + + YYFAIL has existed for many years as an undocumented feature of + deterministic parsers in C generated by Bison. Previously, it was + documented for Bison's experimental Java parsers. YYFAIL is no longer + documented for Java parsers and is formally deprecated in both cases. + Users are strongly encouraged to migrate to YYERROR, which is + specified by POSIX. + + Like YYERROR, you can invoke YYFAIL from a semantic action in order to + induce a syntax error. The most obvious difference from YYERROR is + that YYFAIL will automatically invoke yyerror to report the syntax + error so that you don't have to. However, there are several other + subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from + inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is + used. For a more detailed discussion, see: + + http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html + + The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but + deterministic parsers in C will continue to implement it. However, + because YYFAIL is already flawed, it seems futile to try to make new + Bison features compatible with it. Thus, during parser generation, + Bison 2.5 will produce a warning whenever it discovers YYFAIL in a + rule action. In a later release, YYFAIL will be disabled for + %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will + be removed altogether. + + There exists at least one case where Bison 2.5's YYFAIL warning will + be a false positive. Some projects add phony uses of YYFAIL and other + Bison-defined macros for the sole purpose of suppressing C + preprocessor warnings (from GCC cpp's -Wunused-macros, for example). + To avoid Bison's future warning, such YYFAIL uses can be moved to the + epilogue (that is, after the second `%%') in the Bison input file. In + this release (2.4.2), Bison already generates its own code to suppress + C preprocessor warnings for YYFAIL, so projects can remove their own + phony uses of YYFAIL if compatibility with Bison releases prior to + 2.4.2 is not necessary. + +** Internationalization. + + Fix a regression introduced in Bison 2.4: Under some circumstances, + message translations were not installed although supported by the + host system. + +* Changes in version 2.4.1 (2008-12-11): + +** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc + declarations have been fixed. + +** Temporary hack for adding a semicolon to the user action. + + Bison used to prepend a trailing semicolon at the end of the user + action for reductions. This allowed actions such as + + exp: exp "+" exp { $$ = $1 + $3 }; + + instead of + + exp: exp "+" exp { $$ = $1 + $3; }; + + Some grammars still depend on this `feature'. Bison 2.4.1 restores + the previous behavior in the case of C output (specifically, when + neither %language or %skeleton or equivalent command-line options + are used) to leave more time for grammars depending on the old + behavior to be adjusted. Future releases of Bison will disable this + feature. + +** A few minor improvements to the Bison manual. + +* Changes in version 2.4 (2008-11-02): + +** %language is an experimental feature. + + We first introduced this feature in test release 2.3b as a cleaner + alternative to %skeleton. Since then, we have discussed the possibility of + modifying its effect on Bison's output file names. Thus, in this release, + we consider %language to be an experimental feature that will likely evolve + in future releases. + +** Forward compatibility with GNU M4 has been improved. + +** Several bugs in the C++ skeleton and the experimental Java skeleton have been + fixed. + +* Changes in version 2.3b (2008-05-27): + +** The quotes around NAME that used to be required in the following directive + are now deprecated: + + %define NAME "VALUE" + +** The directive `%pure-parser' is now deprecated in favor of: + + %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 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 STRING1 + %token STRING2 + %type string1 + %type string2 + %union { char character; } + %token CHR + %type chr + %destructor { free ($$); } %symbol-default + %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 + %destructor { } + + guarantees that, when the parser discards any user-defined symbol that has a + semantic type tag other than `', 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) + . + +** 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 bar + %% + bar: '0' {} '0'; + + This is fixed. + +** GNU M4 is now required when using Bison. -Changes in version 1.28: +* Changes in version 1.35, 2002-03-25: -* Should compile better now with K&R compilers. +** 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. -* Added NLS. + 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. -* Fixed a problem with escaping the double quote character. + This kludge also addresses some C++ problems when the stack was + extended. + +* Changes in version 1.34, 2002-03-12: -* There is now a FAQ. +** 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 1.27: +* 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 make rule which prevented bison.simple from being created on +** 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: +* Changes in version 1.26: -* Bison now uses automake. +** Bison now uses automake. -* New mailing lists: and . +** New mailing lists: and . -* Token numbers now start at 257 as previously documented, not 258. +** Token numbers now start at 257 as previously documented, not 258. -* Bison honors the TMPDIR environment variable. +** Bison honors the TMPDIR environment variable. -* A couple of buffer overruns have been fixed. +** A couple of buffer overruns have been fixed. -* Problems when closing files should now be reported. +** Problems when closing files should now be reported. -* Generated parsers should now work even on operating systems which do +** Generated parsers should now work even on operating systems which do not provide alloca(). -Changes in version 1.25: +* Changes in version 1.25, 1995-10-16: -* Errors in the input grammar are not fatal; Bison keeps reading +** Errors in the input grammar are not fatal; Bison keeps reading the grammar file, and reports all the errors found in it. -* Tokens can now be specified as multiple-character strings: for +** Tokens can now be specified as multiple-character strings: for example, you could use "<=" for a token which looks like <=, instead of chosing a name like LESSEQ. -* The %token_table declaration says to write a table of tokens (names +** The %token_table declaration says to write a table of tokens (names and numbers) into the parser file. The yylex function can use this table to recognize multiple-character string tokens, or for other purposes. -* The %no_lines declaration says not to generate any #line preprocessor +** The %no_lines declaration says not to generate any #line preprocessor directives in the parser file. -* The %raw declaration says to use internal Bison token numbers, not +** The %raw declaration says to use internal Bison token numbers, not Yacc-compatible token numbers, when token names are defined as macros. -* The --no-parser option produces the parser tables without including +** The --no-parser option produces the parser tables without including the parser engine; a project can now use its own parser engine. The actions go into a separate file called NAME.act, in the form of a switch statement body. -Changes in version 1.23: +* Changes in version 1.23: The user can define YYPARSE_PARAM as the name of an argument to be passed into yyparse. The argument should have type void *. It should @@ -81,10 +1368,33 @@ by casting it to the proper pointer type. Line numbers in output file corrected. -Changes in version 1.22: +* Changes in version 1.22: --help option added. -Changes in version 1.20: +* Changes in version 1.20: Output file does not redefine const for C++. + +Local Variables: +mode: outline +End: + +----- + +Copyright (C) 1995-2010 Free Software Foundation, Inc. + +This file is part of Bison, the GNU Parser Generator. + +This program is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +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 .