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GNU Bison NEWS * Noteworthy changes in release 3.7.4 (2020-11-14) [stable] ** Bug fixes *** Bug fixes in yacc.c In Yacc mode, all the tokens are defined twice: once as an enum, and then as a macro. YYEMPTY was missing its macro. *** Bug fixes in lalr1.cc The lalr1.cc skeleton used to emit internal assertions (using YY_ASSERT) even when the `parse.assert` %define variable is not enabled. It no longer does. The private internal macro YY_ASSERT now obeys the `api.prefix` %define variable. When there is a very large number of tokens, some assertions could be long enough to hit arbitrary limits in Visual C++. They have been rewritten to work around this limitation. ** Changes The YYBISON macro in generated "regular C parsers" (from the "yacc.c" skeleton) used to be defined to 1. It is now defined to the version of Bison as an integer (e.g., 30704 for version 3.7.4). * Noteworthy changes in release 3.7.3 (2020-10-13) [stable] ** Bug fixes Fix concurrent build issues. The bison executable is no longer linked uselessly against libreadline. Fix incorrect use of yytname in glr.cc. * Noteworthy changes in release 3.7.2 (2020-09-05) [stable] This release of Bison fixes all known bugs reported for Bison in MITRE's Common Vulnerabilities and Exposures (CVE) system. These vulnerabilities are only about bison-the-program itself, not the generated code. Although these bugs are typically irrelevant to how Bison is used, they are worth fixing if only to give users peace of mind. There is no known vulnerability in the generated parsers. ** Bug fixes Fix concurrent build issues (introduced in Bison 3.5). Push parsers always use YYMALLOC/YYFREE (no direct calls to malloc/free). Fix portability issues of the test suite, and of bison itself. Some unlikely crashes found by fuzzing have been fixed. This is only about bison itself, not the generated parsers. * Noteworthy changes in release 3.7.1 (2020-08-02) [stable] ** Bug fixes Crash when a token alias contains a NUL byte. Portability issues with libtextstyle. Portability issues of Bison itself with MSVC. ** Changes Improvements and fixes in the documentation. More precise location about symbol type redefinitions. * Noteworthy changes in release 3.7 (2020-07-23) [stable] ** Deprecated features The YYPRINT macro, which works only with yacc.c and only for tokens, was obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002). It is deprecated and its support will be removed eventually. In conformance with the recommendations of the Graphviz team, in the next version Bison the option `--graph` will generate a *.gv file by default, instead of *.dot. A transition started in Bison 3.4. ** New features *** Counterexample Generation Contributed by Vincent Imbimbo. When given `-Wcounterexamples`/`-Wcex`, bison will now output counterexamples for conflicts. **** Unifying Counterexamples Unifying counterexamples are strings which can be parsed in two ways due to the conflict. For example on a grammar that contains the usual "dangling else" ambiguity: $ bison else.y else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr] else.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples $ bison else.y -Wcex else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr] else.y: warning: shift/reduce conflict on token "else" [-Wcounterexamples] Example: "if" exp "then" "if" exp "then" exp • "else" exp Shift derivation exp ↳ "if" exp "then" exp ↳ "if" exp "then" exp • "else" exp Example: "if" exp "then" "if" exp "then" exp • "else" exp Reduce derivation exp ↳ "if" exp "then" exp "else" exp ↳ "if" exp "then" exp • When text styling is enabled, colors are used in the examples and the derivations to highlight the structure of both analyses. In this case, "if" exp "then" [ "if" exp "then" exp • ] "else" exp vs. "if" exp "then" [ "if" exp "then" exp • "else" exp ] The counterexamples are "focused", in two different ways. First, they do not clutter the output with all the derivations from the start symbol, rather they start on the "conflicted nonterminal". They go straight to the point. Second, they don't "expand" nonterminal symbols uselessly. **** Nonunifying Counterexamples In the case of the dangling else, Bison found an example that can be parsed in two ways (therefore proving that the grammar is ambiguous). When it cannot find such an example, it instead generates two examples that are the same up until the dot: $ bison foo.y foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr] foo.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother] 4 | a: expr | ^~~~ $ bison -Wcex foo.y foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr] foo.y: warning: shift/reduce conflict on token ID [-Wcounterexamples] First example: expr • ID ',' ID $end Shift derivation $accept ↳ s $end ↳ a ID ↳ expr ↳ expr • ID ',' Second example: expr • ID $end Reduce derivation $accept ↳ s $end ↳ a ID ↳ expr • foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother] 4 | a: expr | ^~~~ In these cases, the parser usually doesn't have enough lookahead to differentiate the two given examples. **** Reports Counterexamples are also included in the report when given `--report=counterexamples`/`-rcex` (or `--report=all`), with more technical details: State 7 1 exp: "if" exp "then" exp • [$end, "then", "else"] 2 | "if" exp "then" exp • "else" exp "else" shift, and go to state 8 "else" [reduce using rule 1 (exp)] $default reduce using rule 1 (exp) shift/reduce conflict on token "else": 1 exp: "if" exp "then" exp • 2 exp: "if" exp "then" exp • "else" exp Example: "if" exp "then" "if" exp "then" exp • "else" exp Shift derivation exp ↳ "if" exp "then" exp ↳ "if" exp "then" exp • "else" exp Example: "if" exp "then" "if" exp "then" exp • "else" exp Reduce derivation exp ↳ "if" exp "then" exp "else" exp ↳ "if" exp "then" exp • *** File prefix mapping Contributed by Joshua Watt. Bison learned a new argument, `--file-prefix-map OLD=NEW`. Any file path in the output (specifically `#line` directives and `#ifdef` header guards) that begins with the prefix OLD will have it replaced with the prefix NEW, similar to the `-ffile-prefix-map` in GCC. This option can be used to make bison output reproducible. ** Changes *** Diagnostics When text styling is enabled and the terminal supports it, the warnings now include hyperlinks to the documentation. *** Relocatable installation When installed to be relocatable (via `configure --enable-relocatable`), bison will now also look for a relocated m4. *** C++ file names The `filename_type` %define variable was renamed `api.filename.type`. Instead of %define filename_type "symbol" write %define api.filename.type {symbol} (Or let `bison --update` do it for you). It now defaults to `const std::string` instead of `std::string`. *** Deprecated %define variable names The following variables have been renamed for consistency. Backward compatibility is ensured, but upgrading is recommended. filename_type -> api.filename.type package -> api.package *** Push parsers no longer clear their state when parsing is finished Previously push-parsers cleared their state when parsing was finished (on success and on failure). This made it impossible to check if there were parse errors, since `yynerrs` was also reset. This can be especially troublesome when used in autocompletion, since a parser with error recovery would suggest (irrelevant) expected tokens even if there were failure. Now the parser state can be examined when parsing is finished. The parser state is reset when starting a new parse. ** Documentation *** Examples The bistromathic demonstrates %param and how to quote sources in the error messages: > 123 456 1.5-7: syntax error: expected end of file or + or - or * or / or ^ before number 1 | 123 456 | ^~~ ** Bug fixes *** Include the generated header (yacc.c) Historically, when --defines was used, bison generated a header and pasted an exact copy of it into the generated parser implementation file. Since Bison 3.4 it is possible to specify that the header should be `#include`d, and how. For instance %define api.header.include {"parse.h"} or %define api.header.include {<parser/parse.h>} Now api.header.include defaults to `"header-basename"`, as was intended in Bison 3.4, where `header-basename` is the basename of the generated header. This is disabled when the generated header is `y.tab.h`, to comply with Automake's ylwrap. *** String aliases are faithfully propagated Bison used to interpret user strings (i.e., decoding backslash escapes) when reading them, and to escape them (i.e., issue non-printable characters as backslash escapes, taking the locale into account) when outputting them. As a consequence non-ASCII strings (say in UTF-8) ended up "ciphered" as sequences of backslash escapes. This happened not only in the generated sources (where the compiler will reinterpret them), but also in all the generated reports (text, xml, html, dot, etc.). Reports were therefore not readable when string aliases were not pure ASCII. Worse yet: the output depended on the user's locale. Now Bison faithfully treats the string aliases exactly the way the user spelled them. This fixes all the aforementioned problems. However, now, string aliases semantically equivalent but syntactically different (e.g., "A", "\x41", "\101") are considered to be different. *** Crash when generating IELR An old, well hidden, bug in the generation of IELR parsers was fixed. * Noteworthy changes in release 3.6.4 (2020-06-15) [stable] ** Bug fixes In glr.cc some internal macros leaked in the user's code, and could damage access to the token kinds. * Noteworthy changes in release 3.6.3 (2020-06-03) [stable] ** Bug fixes Incorrect comments in the generated parsers. Warnings in push parsers (yacc.c). Incorrect display of gotos in LAC traces (lalr1.cc). * Noteworthy changes in release 3.6.2 (2020-05-17) [stable] ** Bug fixes Some tests were fixed. When token aliases contain comment delimiters: %token FOO "/* foo */" bison used to emit "nested" comments, which is invalid C. * Noteworthy changes in release 3.6.1 (2020-05-10) [stable] ** Bug fixes Restored ANSI-C compliance in yacc.c. GNU readline portability issues. In C++, yy::parser::symbol_name is now a public member, as was intended. ** New features In C++, yy::parser::symbol_type now has a public name() member function. * Noteworthy changes in release 3.6 (2020-05-08) [stable] ** Backward incompatible changes TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose". The YYERROR_VERBOSE macro is no longer supported; the parsers that still depend on it will now produce Yacc-like error messages (just "syntax error"). It was superseded by the "%error-verbose" directive in Bison 1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that support for YYERROR_VERBOSE would be removed. Note that since Bison 3.0 (2013-07-25), "%error-verbose" is deprecated in favor of "%define parse.error verbose". ** Deprecated features The YYPRINT macro, which works only with yacc.c and only for tokens, was obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002). It is deprecated and its support will be removed eventually. ** New features *** Improved syntax error messages Two new values for the %define parse.error variable offer more control to the user. Available in all the skeletons (C, C++, Java). **** %define parse.error detailed The behavior of "%define parse.error detailed" is closely resembling that of "%define parse.error verbose" with a few exceptions. First, it is safe to use non-ASCII characters in token aliases (with 'verbose', the result depends on the locale with which bison was run). Second, a yysymbol_name function is exposed to the user, instead of the yytnamerr function and the yytname table. Third, token internationalization is supported (see below). **** %define parse.error custom With this directive, the user forges and emits the syntax error message herself by defining the yyreport_syntax_error function. A new type, yypcontext_t, captures the circumstances of the error, and provides the user with functions to get details, such as yypcontext_expected_tokens to get the list of expected token kinds. A possible implementation of yyreport_syntax_error is: int yyreport_syntax_error (const yypcontext_t *ctx) { int res = 0; YY_LOCATION_PRINT (stderr, *yypcontext_location (ctx)); fprintf (stderr, ": syntax error"); // Report the tokens expected at this point. { enum { TOKENMAX = 10 }; yysymbol_kind_t expected[TOKENMAX]; int n = yypcontext_expected_tokens (ctx, expected, TOKENMAX); if (n < 0) // Forward errors to yyparse. res = n; else for (int i = 0; i < n; ++i) fprintf (stderr, "%s %s", i == 0 ? ": expected" : " or", yysymbol_name (expected[i])); } // Report the unexpected token. { yysymbol_kind_t lookahead = yypcontext_token (ctx); if (lookahead != YYSYMBOL_YYEMPTY) fprintf (stderr, " before %s", yysymbol_name (lookahead)); } fprintf (stderr, "\n"); return res; } **** Token aliases internationalization When the %define variable parse.error is set to `custom` or `detailed`, one may specify which token aliases are to be translated using _(). For instance %token PLUS "+" MINUS "-" <double> NUM _("number") <symrec*> FUN _("function") VAR _("variable") In that case the user must define _() and N_(), and yysymbol_name returns the translated symbol (i.e., it returns '_("variable")' rather that '"variable"'). In Java, the user must provide an i18n() function. *** List of expected tokens (yacc.c) Push parsers may invoke yypstate_expected_tokens at any point during parsing (including even before submitting the first token) to get the list of possible tokens. This feature can be used to propose autocompletion (see below the "bistromathic" example). It makes little sense to use this feature without enabling LAC (lookahead correction). *** Returning the error token When the scanner returns an invalid token or the undefined token (YYUNDEF), the parser generates an error message and enters error recovery. Because of that error message, most scanners that find lexical errors generate an error message, and then ignore the invalid input without entering the error-recovery. The scanners may now return YYerror, the error token, to enter the error-recovery mode without triggering an additional error message. See the bistromathic for an example. *** Deep overhaul of the symbol and token kinds To avoid the confusion with types in programming languages, we now refer to token and symbol "kinds" instead of token and symbol "types". The documentation and error messages have been revised. All the skeletons have been updated to use dedicated enum types rather than integral types. Special symbols are now regular citizens, instead of being declared in ad hoc ways. **** Token kinds The "token kind" is what is returned by the scanner, e.g., PLUS, NUMBER, LPAREN, etc. While backward compatibility is of course ensured, users are nonetheless invited to replace their uses of "enum yytokentype" by "yytoken_kind_t". This type now also includes tokens that were previously hidden: YYEOF (end of input), YYUNDEF (undefined token), and YYerror (error token). They now have string aliases, internationalized when internationalization is enabled. Therefore, by default, error messages now refer to "end of file" (internationalized) rather than the cryptic "$end", or to "invalid token" rather than "$undefined". Therefore in most cases it is now useless to define the end-of-line token as follows: %token T_EOF 0 "end of file" Rather simply use "YYEOF" in your scanner. **** Symbol kinds The "symbol kinds" is what the parser actually uses. (Unless the api.token.raw %define variable is used, the symbol kind of a terminal differs from the corresponding token kind.) They are now exposed as a enum, "yysymbol_kind_t". This allows users to tailor the error messages the way they want, or to process some symbols in a specific way in autocompletion (see the bistromathic example below). *** Modernize display of explanatory statements in diagnostics Since Bison 2.7, output was indented four spaces for explanatory statements. For example: input.y:2.7-13: error: %type redeclaration for exp input.y:1.7-11: previous declaration Since the introduction of caret-diagnostics, it became less clear. This indentation has been removed and submessages are displayed similarly as in GCC: input.y:2.7-13: error: %type redeclaration for exp 2 | %type <float> exp | ^~~~~~~ input.y:1.7-11: note: previous declaration 1 | %type <int> exp | ^~~~~ Contributed by Victor Morales Cayuela. *** C++ The token and symbol kinds are yy::parser::token_kind_type and yy::parser::symbol_kind_type. The symbol_type::kind() member function allows to get the kind of a symbol. This can be used to write unit tests for scanners, e.g., yy::parser::symbol_type t = make_NUMBER ("123"); assert (t.kind () == yy::parser::symbol_kind::S_NUMBER); assert (t.value.as<int> () == 123); ** Documentation *** User Manual In order to avoid ambiguities with "type" as in "typing", we now refer to the "token kind" (e.g., `PLUS`, `NUMBER`, etc.) rather than the "token type". We now also refer to the "symbol type" (e.g., `PLUS`, `expr`, etc.). *** Examples There are now examples/java: a very simple calculator, and a more complete one (push-parser, location tracking, and debug traces). The lexcalc example (a simple example in C based on Flex and Bison) now also demonstrates location tracking. A new C example, bistromathic, is a fully featured interactive calculator using many Bison features: pure interface, push parser, autocompletion based on the current parser state (using yypstate_expected_tokens), location tracking, internationalized custom error messages, lookahead correction, rich debug traces, etc. It shows how to depend on the symbol kinds to tailor autocompletion. For instance it recognizes the symbol kind "VARIABLE" to propose autocompletion on the existing variables, rather than of the word "variable". * Noteworthy changes in release 3.5.4 (2020-04-05) [stable] ** WARNING: Future backward-incompatibilities! TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose". Bison 3.6 will no longer support the YYERROR_VERBOSE macro; the parsers that still depend on it will produce Yacc-like error messages (just "syntax error"). It was superseded by the "%error-verbose" directive in Bison 1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that support for YYERROR_VERBOSE would be removed. Note that since Bison 3.0 (2013-07-25), "%error-verbose" is deprecated in favor of "%define parse.error verbose". ** Bug fixes Fix portability issues of the package itself on old compilers. Fix api.token.raw support in Java. * Noteworthy changes in release 3.5.3 (2020-03-08) [stable] ** Bug fixes Error messages could quote lines containing zero-width characters (such as \005) with incorrect styling. Fixes for similar issues with unexpectedly short lines (e.g., the file was changed between parsing and diagnosing). Some unlikely crashes found by fuzzing have been fixed. This is only about bison itself, not the generated parsers. * Noteworthy changes in release 3.5.2 (2020-02-13) [stable] ** Bug fixes Portability issues and minor cosmetic issues. The lalr1.cc skeleton properly rejects unsupported values for parse.lac (as yacc.c does). * Noteworthy changes in release 3.5.1 (2020-01-19) [stable] ** Bug fixes Portability fixes. Fix compiler warnings. * Noteworthy changes in release 3.5 (2019-12-11) [stable] ** Backward incompatible changes Lone carriage-return characters (aka \r or ^M) in the grammar files are no longer treated as end-of-lines. This changes the diagnostics, and in particular their locations. In C++, line numbers and columns are now represented as 'int' not 'unsigned', so that integer overflow on positions is easily checkable via 'gcc -fsanitize=undefined' and the like. This affects the API for positions. The default position and location classes now expose 'counter_type' (int), used to define line and column numbers. ** Deprecated features The YYPRINT macro, which works only with yacc.c and only for tokens, was obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002). It is deprecated and its support will be removed eventually. ** New features *** Lookahead correction in C++ Contributed by Adrian Vogelsgesang. The C++ deterministic skeleton (lalr1.cc) now supports LAC, via the %define variable parse.lac. *** Variable api.token.raw: Optimized token numbers (all skeletons) In the generated parsers, tokens have two numbers: the "external" token number as returned by yylex (which starts at 257), and the "internal" symbol number (which starts at 3). Each time yylex is called, a table lookup maps the external token number to the internal symbol number. When the %define variable api.token.raw is set, tokens are assigned their internal number, which saves one table lookup per token, and also saves the generation of the mapping table. The gain is typically moderate, but in extreme cases (very simple user actions), a 10% improvement can be observed. *** Generated parsers use better types for states Stacks now use the best integral type for state numbers, instead of always using 15 bits. As a result "small" parsers now have a smaller memory footprint (they use 8 bits), and there is support for large automata (16 bits), and extra large (using int, i.e., typically 31 bits). *** Generated parsers prefer signed integer types Bison skeletons now prefer signed to unsigned integer types when either will do, as the signed types are less error-prone and allow for better checking with 'gcc -fsanitize=undefined'. Also, the types chosen are now portable to unusual machines where char, short and int are all the same width. On non-GNU platforms this may entail including <limits.h> and (if available) <stdint.h> to define integer types and constants. *** A skeleton for the D programming language For the last few releases, Bison has shipped a stealth experimental skeleton: lalr1.d. It was first contributed by Oliver Mangold, based on Paolo Bonzini's lalr1.java, and was cleaned and improved thanks to H. S. Teoh. However, because nobody has committed to improving, testing, and documenting this skeleton, it is not clear that it will be supported in the future. The lalr1.d skeleton *is functional*, and works well, as demonstrated in examples/d/calc.d. Please try it, enjoy it, and... commit to support it. *** Debug traces in Java The Java backend no longer emits code and data for parser tracing if the %define variable parse.trace is not defined. ** Diagnostics *** New diagnostic: -Wdangling-alias String literals, which allow for better error messages, are (too) liberally accepted by Bison, which might result in silent errors. For instance %type <exVal> cond "condition" does not define "condition" as a string alias to 'cond' (nonterminal symbols do not have string aliases). It is rather equivalent to %nterm <exVal> cond %token <exVal> "condition" i.e., it gives the type 'exVal' to the "condition" token, which was clearly not the intention. Also, because string aliases need not be defined, typos such as "baz" instead of "bar" will be not reported. The option -Wdangling-alias catches these situations. On %token BAR "bar" %type <ival> foo "foo" %% foo: "baz" {} bison -Wdangling-alias reports warning: string literal not attached to a symbol | %type <ival> foo "foo" | ^~~~~ warning: string literal not attached to a symbol | foo: "baz" {} | ^~~~~ The -Wall option does not (yet?) include -Wdangling-alias. *** Better POSIX Yacc compatibility diagnostics POSIX Yacc restricts %type to nonterminals. This is now diagnosed by -Wyacc. %token TOKEN1 %type <ival> TOKEN1 TOKEN2 't' %token TOKEN2 %% expr: gives with -Wyacc input.y:2.15-20: warning: POSIX yacc reserves %type to nonterminals [-Wyacc] 2 | %type <ival> TOKEN1 TOKEN2 't' | ^~~~~~ input.y:2.29-31: warning: POSIX yacc reserves %type to nonterminals [-Wyacc] 2 | %type <ival> TOKEN1 TOKEN2 't' | ^~~ input.y:2.22-27: warning: POSIX yacc reserves %type to nonterminals [-Wyacc] 2 | %type <ival> TOKEN1 TOKEN2 't' | ^~~~~~ *** Diagnostics with insertion The diagnostics now display the suggestion below the underlined source. Replacement for undeclared symbols are now also suggested. $ cat /tmp/foo.y %% list: lis '.' | $ bison -Wall foo.y foo.y:2.7-9: error: symbol 'lis' is used, but is not defined as a token and has no rules; did you mean 'list'? 2 | list: lis '.' | | ^~~ | list foo.y:2.16: warning: empty rule without %empty [-Wempty-rule] 2 | list: lis '.' | | ^ | %empty foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother] *** Diagnostics about long lines Quoted sources may now be truncated to fit the screen. For instance, on a 30-column wide terminal: $ cat foo.y %token FOO FOO FOO %% exp: FOO $ bison foo.y foo.y:1.34-36: warning: symbol FOO redeclared [-Wother] 1 | … FOO … | ^~~ foo.y:1.8-10: previous declaration 1 | %token FOO … | ^~~ foo.y:1.62-64: warning: symbol FOO redeclared [-Wother] 1 | … FOO | ^~~ foo.y:1.8-10: previous declaration 1 | %token FOO … | ^~~ ** Changes *** Debugging glr.c and glr.cc The glr.c skeleton always had asserts to check its own behavior (not the user's). These assertions are now under the control of the parse.assert %define variable (disabled by default). *** Clean up Several new compiler warnings in the generated output have been avoided. Some unused features are no longer emitted. Cleaner generated code in general. ** Bug Fixes Portability issues in the test suite. In theory, parsers using %nonassoc could crash when reporting verbose error messages. This unlikely bug has been fixed. In Java, %define api.prefix was ignored. It now behaves as expected. * Noteworthy changes in release 3.4.2 (2019-09-12) [stable] ** Bug fixes In some cases, when warnings are disabled, bison could emit tons of white spaces as diagnostics. When running out of memory, bison could crash (found by fuzzing). When defining twice the EOF token, bison would crash. New warnings from recent compilers have been addressed in the generated parsers (yacc.c, glr.c, glr.cc). When lone carriage-return characters appeared in the input file, diagnostics could hang forever. * Noteworthy changes in release 3.4.1 (2019-05-22) [stable] ** Bug fixes Portability fixes. * Noteworthy changes in release 3.4 (2019-05-19) [stable] ** Deprecated features The %pure-parser directive is deprecated in favor of '%define api.pure' since Bison 2.3b (2008-05-27), but no warning was issued; there is one now. Note that since Bison 2.7 you are strongly encouraged to use '%define api.pure full' instead of '%define api.pure'. ** New features *** Colored diagnostics As an experimental feature, diagnostics are now colored, controlled by the new options --color and --style. To use them, install the libtextstyle library before configuring Bison. It is available from https://alpha.gnu.org/gnu/gettext/ for instance https://alpha.gnu.org/gnu/gettext/libtextstyle-0.8.tar.gz The option --color supports the following arguments: - always, yes: Enable colors. - never, no: Disable colors. - auto, tty (default): Enable colors if the output device is a tty. To customize the styles, create a CSS file similar to /* bison-bw.css */ .warning { } .error { font-weight: 800; text-decoration: underline; } .note { } then invoke bison with --style=bison-bw.css, or set the BISON_STYLE environment variable to "bison-bw.css". *** Disabling output When given -fsyntax-only, the diagnostics are reported, but no output is generated. The name of this option is somewhat misleading as bison does more than just checking the syntax: every stage is run (including checking for conflicts for instance), except the generation of the output files. *** Include the generated header (yacc.c) Before, when --defines is used, bison generated a header, and pasted an exact copy of it into the generated parser implementation file. If the header name is not "y.tab.h", it is now #included instead of being duplicated. To use an '#include' even if the header name is "y.tab.h" (which is what happens with --yacc, or when using the Autotools' ylwrap), define api.header.include to the exact argument to pass to #include. For instance: %define api.header.include {"parse.h"} or %define api.header.include {<parser/parse.h>} *** api.location.type is now supported in C (yacc.c, glr.c) The %define variable api.location.type defines the name of the type to use for locations. When defined, Bison no longer defines YYLTYPE. This can be used in programs with several parsers to factor their definition of locations: let one of them generate them, and the others just use them. ** Changes *** Graphviz output In conformance with the recommendations of the Graphviz team, if %require "3.4" (or better) is specified, the option --graph generates a *.gv file by default, instead of *.dot. *** Diagnostics overhaul Column numbers were wrong with multibyte characters, which would also result in skewed diagnostics with carets. Beside, because we were indenting the quoted source with a single space, lines with tab characters were incorrectly underlined. To address these issues, and to be clearer, Bison now issues diagnostics as GCC9 does. For instance it used to display (there's a tab before the opening brace): foo.y:3.37-38: error: $2 of ‘expr’ has no declared type expr: expr '+' "number" { $$ = $1 + $2; } ^~ It now reports foo.y:3.37-38: error: $2 of ‘expr’ has no declared type 3 | expr: expr '+' "number" { $$ = $1 + $2; } | ^~ Other constructs now also have better locations, resulting in more precise diagnostics. *** Fix-it hints for %empty Running Bison with -Wempty-rules and --update will remove incorrect %empty annotations, and add the missing ones. *** Generated reports The format of the reports (parse.output) was improved for readability. *** Better support for --no-line. When --no-line is used, the generated files are now cleaner: no lines are generated instead of empty lines. Together with using api.header.include, that should help people saving the generated files into version control systems get smaller diffs. ** Documentation A new example in C shows an simple infix calculator with a hand-written scanner (examples/c/calc). A new example in C shows a reentrant parser (capable of recursive calls) built with Flex and Bison (examples/c/reccalc). There is a new section about the history of Yaccs and Bison. ** Bug fixes A few obscure bugs were fixed, including the second oldest (known) bug in Bison: it was there when Bison was entered in the RCS version control system, in December 1987. See the NEWS of Bison 3.3 for the previous oldest bug. * Noteworthy changes in release 3.3.2 (2019-02-03) [stable] ** Bug fixes Bison 3.3 failed to generate parsers for grammars with unused nonterminal symbols. * Noteworthy changes in release 3.3.1 (2019-01-27) [stable] ** Changes The option -y/--yacc used to imply -Werror=yacc, which turns uses of Bison extensions into errors. It now makes them simple warnings (-Wyacc). * Noteworthy changes in release 3.3 (2019-01-26) [stable] A new mailing list was created, Bison Announce. It is low traffic, and is only about announcing new releases and important messages (e.g., polls about major decisions to make). https://lists.gnu.org/mailman/listinfo/bison-announce ** Backward incompatible changes Support for DJGPP, which has been unmaintained and untested for years, is removed. ** Deprecated features A new feature, --update (see below) helps adjusting existing grammars to deprecations. *** Deprecated directives The %error-verbose directive is deprecated in favor of '%define parse.error verbose' since Bison 3.0, but no warning was issued. The '%name-prefix "xx"' directive is deprecated in favor of '%define api.prefix {xx}' since Bison 3.0, but no warning was issued. These directives are slightly different, you might need to adjust your code. %name-prefix renames only symbols with external linkage, while api.prefix also renames types and macros, including YYDEBUG, YYTOKENTYPE, yytokentype, YYSTYPE, YYLTYPE, etc. Users of Flex that move from '%name-prefix "xx"' to '%define api.prefix {xx}' will typically have to update YY_DECL from #define YY_DECL int xxlex (YYSTYPE *yylval, YYLTYPE *yylloc) to #define YY_DECL int xxlex (XXSTYPE *yylval, XXLTYPE *yylloc) *** Deprecated %define variable names The following variables, mostly related to parsers in Java, have been renamed for consistency. Backward compatibility is ensured, but upgrading is recommended. abstract -> api.parser.abstract annotations -> api.parser.annotations extends -> api.parser.extends final -> api.parser.final implements -> api.parser.implements parser_class_name -> api.parser.class public -> api.parser.public strictfp -> api.parser.strictfp ** New features *** Generation of fix-its for IDEs/Editors When given the new option -ffixit (aka -fdiagnostics-parseable-fixits), bison now generates machine readable editing instructions to fix some issues. Currently, this is mostly limited to updating deprecated directives and removing duplicates. For instance: $ cat foo.y %error-verbose %define parser_class_name "Parser" %define api.parser.class "Parser" %% exp:; See the "fix-it:" lines below: $ bison -ffixit foo.y foo.y:1.1-14: warning: deprecated directive, use '%define parse.error verbose' [-Wdeprecated] %error-verbose ^~~~~~~~~~~~~~ fix-it:"foo.y":{1:1-1:15}:"%define parse.error verbose" foo.y:2.1-34: warning: deprecated directive, use '%define api.parser.class {Parser}' [-Wdeprecated] %define parser_class_name "Parser" ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ fix-it:"foo.y":{2:1-2:35}:"%define api.parser.class {Parser}" foo.y:3.1-33: error: %define variable 'api.parser.class' redefined %define api.parser.class "Parser" ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ foo.y:2.1-34: previous definition %define parser_class_name "Parser" ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ fix-it:"foo.y":{3:1-3:34}:"" foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother] This uses the same output format as GCC and Clang. *** Updating grammar files Fixes can be applied on the fly. The previous example ends with the suggestion to re-run bison with the option -u/--update, which results in a cleaner grammar file. $ bison --update foo.y [...] bison: file 'foo.y' was updated (backup: 'foo.y~') $ cat foo.y %define parse.error verbose %define api.parser.class {Parser} %% exp:; *** Bison is now relocatable If you pass '--enable-relocatable' to 'configure', Bison is relocatable. A relocatable program can be moved or copied to a different location on the file system. It can also be used through mount points for network sharing. It is possible to make symbolic links to the installed and moved programs, and invoke them through the symbolic link. *** %expect and %expect-rr modifiers on individual rules One can now document (and check) which rules participate in shift/reduce and reduce/reduce conflicts. This is particularly important GLR parsers, where conflicts are a normal occurrence. For example, %glr-parser %expect 1 %% ... argument_list: arguments %expect 1 | arguments ',' | %empty ; arguments: expression | argument_list ',' expression ; ... Looking at the output from -v, one can see that the shift/reduce conflict here is due to the fact that the parser does not know whether to reduce arguments to argument_list until it sees the token _after_ the following ','. By marking the rule with %expect 1 (because there is a conflict in one state), we document the source of the 1 overall shift/reduce conflict. In GLR parsers, we can use %expect-rr in a rule for reduce/reduce conflicts. In this case, we mark each of the conflicting rules. For example, %glr-parser %expect-rr 1 %% stmt: target_list '=' expr ';' | expr_list ';' ; target_list: target | target ',' target_list ; target: ID %expect-rr 1 ; expr_list: expr | expr ',' expr_list ; expr: ID %expect-rr 1 | ... ; In a statement such as x, y = 3, 4; the parser must reduce x to a target or an expr, but does not know which until it sees the '='. So we notate the two possible reductions to indicate that each conflicts in one rule. This feature needs user feedback, and might evolve in the future. *** C++: Actual token constructors When variants and token constructors are enabled, in addition to the type-safe named token constructors (make_ID, make_INT, etc.), we now generate genuine constructors for symbol_type. For instance with these declarations %token ':' <std::string> ID <int> INT; you may use these constructors: symbol_type (int token, const std::string&); symbol_type (int token, const int&); symbol_type (int token); Correct matching between token types and value types is checked via 'assert'; for instance, 'symbol_type (ID, 42)' would abort. Named constructors are preferable, as they offer better type safety (for instance 'make_ID (42)' would not even compile), but symbol_type constructors may help when token types are discovered at run-time, e.g., [a-z]+ { if (auto i = lookup_keyword (yytext)) return yy::parser::symbol_type (i); else return yy::parser::make_ID (yytext); } *** C++: Variadic emplace If your application requires C++11 and you don't use symbol constructors, you may now use a variadic emplace for semantic values: %define api.value.type variant %token <std::pair<int, int>> PAIR in your scanner: int yylex (parser::semantic_type *lvalp) { lvalp->emplace <std::pair<int, int>> (1, 2); return parser::token::PAIR; } *** C++: Syntax error exceptions in GLR The glr.cc skeleton now supports syntax_error exceptions thrown from user actions, or from the scanner. *** More POSIX Yacc compatibility warnings More Bison specific directives are now reported with -y or -Wyacc. This change was ready since the release of Bison 3.0 in September 2015. It was delayed because Autoconf used to define YACC as `bison -y`, which resulted in numerous warnings for Bison users that use the GNU Build System. If you still experience that problem, either redefine YACC as `bison -o y.tab.c`, or pass -Wno-yacc to Bison. *** The tables yyrhs and yyphrs are back Because no Bison skeleton uses them, these tables were removed (no longer passed to the skeletons, not even computed) in 2008. However, some users have expressed interest in being able to use them in their own skeletons. ** Bug fixes *** Incorrect number of reduce/reduce conflicts On a grammar such as exp: "num" | "num" | "num" bison used to report a single RR conflict, instead of two. This is now fixed. This was the oldest (known) bug in Bison: it was there when Bison was entered in the RCS version control system, in December 1987. Some grammar files might have to adjust their %expect-rr. *** Parser directives that were not careful enough Passing invalid arguments to %nterm, for instance character literals, used to result in unclear error messages. ** Documentation The examples/ directory (installed in .../share/doc/bison/examples) has been restructured per language for clarity. The examples come with a README and a Makefile. Not only can they be used to toy with Bison, they can also be starting points for your own grammars. There is now a Java example, and a simple example in C based on Flex and Bison (examples/c/lexcalc/). ** Changes *** Parsers in C++ They now use noexcept and constexpr. Please, report missing annotations. *** Symbol Declarations The syntax of the variation directives to declare symbols was overhauled for more consistency, and also better POSIX Yacc compliance (which, for instance, allows "%type" without actually providing a type). The %nterm directive, supported by Bison since its inception, is now documented and officially supported. The syntax is now as follows: %token TAG? ( ID NUMBER? STRING? )+ ( TAG ( ID NUMBER? STRING? )+ )* %left TAG? ( ID NUMBER? )+ ( TAG ( ID NUMBER? )+ )* %type TAG? ( ID | CHAR | STRING )+ ( TAG ( ID | CHAR | STRING )+ )* %nterm TAG? ID+ ( TAG ID+ )* where TAG denotes a type tag such as ‘<ival>’, ID denotes an identifier such as ‘NUM’, NUMBER a decimal or hexadecimal integer such as ‘300’ or ‘0x12d’, CHAR a character literal such as ‘'+'’, and STRING a string literal such as ‘"number"’. The post-fix quantifiers are ‘?’ (zero or one), ‘*’ (zero or more) and ‘+’ (one or more). * Noteworthy changes in release 3.2.4 (2018-12-24) [stable] ** Bug fixes Fix the move constructor of symbol_type. Always provide a copy constructor for symbol_type, even in modern C++. * Noteworthy changes in release 3.2.3 (2018-12-18) [stable] ** Bug fixes Properly support token constructors in C++ with types that include commas (e.g., std::pair<int, int>). A regression introduced in Bison 3.2. * Noteworthy changes in release 3.2.2 (2018-11-21) [stable] ** Bug fixes C++ portability issues. * Noteworthy changes in release 3.2.1 (2018-11-09) [stable] ** Bug fixes Several portability issues have been fixed in the build system, in the test suite, and in the generated parsers in C++. * Noteworthy changes in release 3.2 (2018-10-29) [stable] ** Backward incompatible changes Support for DJGPP, which has been unmaintained and untested for years, is obsolete. Unless there is activity to revive it, it will be removed. ** Changes %printers should use yyo rather than yyoutput to denote the output stream. Variant-based symbols in C++ should use emplace() rather than build(). In C++ parsers, parser::operator() is now a synonym for the parser::parse. ** Documentation A new section, "A Simple C++ Example", is a tutorial for parsers in C++. A comment in the generated code now emphasizes that users should not depend upon non-documented implementation details, such as macros starting with YY_. ** New features *** C++: Support for move semantics (lalr1.cc) The lalr1.cc skeleton now fully supports C++ move semantics, while maintaining compatibility with C++98. You may now store move-only types when using Bison's variants. For instance: %code { #include <memory> #include <vector> } %skeleton "lalr1.cc" %define api.value.type variant %% %token <int> INT "int"; %type <std::unique_ptr<int>> int; %type <std::vector<std::unique_ptr<int>>> list; list: %empty {} | list int { $$ = std::move($1); $$.emplace_back(std::move($2)); } int: "int" { $$ = std::make_unique<int>($1); } *** C++: Implicit move of right-hand side values (lalr1.cc) In modern C++ (C++11 and later), you should always use 'std::move' with the values of the right-hand side symbols ($1, $2, etc.), as they will be popped from the stack anyway. Using 'std::move' is mandatory for move-only types such as unique_ptr, and it provides a significant speedup for large types such as std::string, or std::vector, etc. If '%define api.value.automove' is set, every occurrence '$n' is replaced by 'std::move ($n)'. The second rule in the previous grammar can be simplified to: list: list int { $$ = $1; $$.emplace_back($2); } With automove enabled, the semantic values are no longer lvalues, so do not use the swap idiom: list: list int { std::swap($$, $1); $$.emplace_back($2); } This idiom is anyway obsolete: it is preferable to move than to swap. A warning is issued when automove is enabled, and a value is used several times. input.yy:16.31-32: warning: multiple occurrences of $2 with api.value.automove enabled [-Wother] exp: "twice" exp { $$ = $2 + $2; } ^^ Enabling api.value.automove does not require support for modern C++. The generated code is valid C++98/03, but will use copies instead of moves. The new examples/c++/variant-11.yy shows these features in action. *** C++: The implicit default semantic action is always run When variants are enabled, the default action was not run, so exp: "number" was equivalent to exp: "number" {} It now behaves like in all the other cases, as exp: "number" { $$ = $1; } possibly using std::move if automove is enabled. We do not expect backward compatibility issues. However, beware of forward compatibility issues: if you rely on default actions with variants, be sure to '%require "3.2"' to avoid older versions of Bison to generate incorrect parsers. *** C++: Renaming location.hh When both %defines and %locations are enabled, Bison generates a location.hh file. If you don't use locations outside of the parser, you may avoid its creation with: %define api.location.file none However this file is useful if, for instance, your parser builds an AST decorated with locations: you may use Bison's location independently of Bison's parser. You can now give it another name, for instance: %define api.location.file "my-location.hh" This name can have directory components, and even be absolute. The name under which the location file is included is controlled by api.location.include. This way it is possible to have several parsers share the same location file. For instance, in src/foo/parser.hh, generate the include/ast/loc.hh file: %locations %define api.namespace {foo} %define api.location.file "include/ast/loc.hh" %define api.location.include {<ast/loc.hh>} and use it in src/bar/parser.hh: %locations %define api.namespace {bar} %code requires {#include <ast/loc.hh>} %define api.location.type {bar::location} Absolute file names are supported, so in your Makefile, passing the flag -Dapi.location.file='"$(top_srcdir)/include/ast/location.hh"' to bison is safe. *** C++: stack.hh and position.hh are deprecated When asked to generate a header file (%defines), the lalr1.cc skeleton generates a stack.hh file. This file had no interest for users; it is now made useless: its content is included in the parser definition. It is still generated for backward compatibility. When in addition to %defines, location support is requested (%locations), the file position.hh is also generated. It is now also useless: its content is now included in location.hh. These files are no longer generated when your grammar file requires at least Bison 3.2 (%require "3.2"). ** Bug fixes Portability issues on MinGW and VS2015. Portability issues in the test suite. Portability/warning issues with Flex. * Noteworthy changes in release 3.1 (2018-08-27) [stable] ** Backward incompatible changes Compiling Bison now requires a C99 compiler---as announced during the release of Bison 3.0, five years ago. Generated parsers do not require a C99 compiler. Support for DJGPP, which has been unmaintained and untested for years, is obsolete. Unless there is activity to revive it, the next release of Bison will have it removed. ** New features *** Typed midrule actions Because their type is unknown to Bison, the values of midrule actions are not treated like the others: they don't have %printer and %destructor support. It also prevents C++ (Bison) variants to handle them properly. Typed midrule actions address these issues. Instead of: exp: { $<ival>$ = 1; } { $<ival>$ = 2; } { $$ = $<ival>1 + $<ival>2; } write: exp: <ival>{ $$ = 1; } <ival>{ $$ = 2; } { $$ = $1 + $2; } *** Reports include the type of the symbols The sections about terminal and nonterminal symbols of the '*.output' file now specify their declared type. For instance, for: %token <ival> NUM the report now shows '<ival>': Terminals, with rules where they appear NUM <ival> (258) 5 *** Diagnostics about useless rules In the following grammar, the 'exp' nonterminal is trivially useless. So, of course, its rules are useless too. %% input: '0' | exp exp: exp '+' exp | exp '-' exp | '(' exp ')' Previously all the useless rules were reported, including those whose left-hand side is the 'exp' nonterminal: warning: 1 nonterminal useless in grammar [-Wother] warning: 4 rules useless in grammar [-Wother] 2.14-16: warning: nonterminal useless in grammar: exp [-Wother] input: '0' | exp ^^^ 2.14-16: warning: rule useless in grammar [-Wother] input: '0' | exp ^^^ 3.6-16: warning: rule useless in grammar [-Wother] exp: exp '+' exp | exp '-' exp | '(' exp ')' ^^^^^^^^^^^ 3.20-30: warning: rule useless in grammar [-Wother] exp: exp '+' exp | exp '-' exp | '(' exp ')' ^^^^^^^^^^^ 3.34-44: warning: rule useless in grammar [-Wother] exp: exp '+' exp | exp '-' exp | '(' exp ')' ^^^^^^^^^^^ Now, rules whose left-hand side symbol is useless are no longer reported as useless. The locations of the errors have also been adjusted to point to the first use of the nonterminal as a left-hand side of a rule: warning: 1 nonterminal useless in grammar [-Wother] warning: 4 rules useless in grammar [-Wother] 3.1-3: warning: nonterminal useless in grammar: exp [-Wother] exp: exp '+' exp | exp '-' exp | '(' exp ')' ^^^ 2.14-16: warning: rule useless in grammar [-Wother] input: '0' | exp ^^^ *** C++: Generated parsers can be compiled with -fno-exceptions (lalr1.cc) When compiled with exceptions disabled, the generated parsers no longer uses try/catch clauses. Currently only GCC and Clang are supported. ** Documentation *** A demonstration of variants A new example was added (installed in .../share/doc/bison/examples), 'variant.yy', which shows how to use (Bison) variants in C++. The other examples were made nicer to read. *** Some features are no longer 'experimental' The following features, mature enough, are no longer flagged as experimental in the documentation: push parsers, default %printer and %destructor (typed: <*> and untyped: <>), %define api.value.type union and variant, Java parsers, XML output, LR family (lr, ielr, lalr), and semantic predicates (%?). ** Bug fixes *** GLR: Predicates support broken by #line directives Predicates (%?) in GLR such as widget: %? {new_syntax} 'w' id new_args | %?{!new_syntax} 'w' id old_args were issued with #lines in the middle of C code. *** Printer and destructor with broken #line directives The #line directives were not properly escaped when emitting the code for %printer/%destructor, which resulted in compiler errors if there are backslashes or double-quotes in the grammar file name. *** Portability on ICC The Intel compiler claims compatibility with GCC, yet rejects its _Pragma. Generated parsers now work around this. *** Various There were several small fixes in the test suite and in the build system, many warnings in bison and in the generated parsers were eliminated. The documentation also received its share of minor improvements. Useless code was removed from C++ parsers, and some of the generated constructors are more 'natural'. * Noteworthy changes in release 3.0.5 (2018-05-27) [stable] ** Bug fixes *** C++: Fix support of 'syntax_error' One incorrect 'inline' resulted in linking errors about the constructor of the syntax_error exception. *** C++: Fix warnings GCC 7.3 (with -O1 or -O2 but not -O0 or -O3) issued null-dereference warnings about yyformat being possibly null. It also warned about the deprecated implicit definition of copy constructors when there's a user-defined (copy) assignment operator. *** Location of errors In C++ parsers, out-of-bounds errors can happen when a rule with an empty ride-hand side raises a syntax error. The behavior of the default parser (yacc.c) in such a condition was undefined. Now all the parsers match the behavior of glr.c: @$ is used as the location of the error. This handles gracefully rules with and without rhs. *** Portability fixes in the test suite On some platforms, some Java and/or C++ tests were failing. * Noteworthy changes in release 3.0.4 (2015-01-23) [stable] ** Bug fixes *** C++ with Variants (lalr1.cc) Fix a compiler warning when no %destructor use $$. *** Test suites Several portability issues in tests were fixed. * Noteworthy changes in release 3.0.3 (2015-01-15) [stable] ** Bug fixes *** C++ with Variants (lalr1.cc) Problems with %destructor and '%define parse.assert' have been fixed. *** Named %union support (yacc.c, glr.c) Bison 3.0 introduced a regression on named %union such as %union foo { int ival; }; The possibility to use a name was introduced "for Yacc compatibility". It is however not required by POSIX Yacc, and its usefulness is not clear. *** %define api.value.type union with %defines (yacc.c, glr.c) The C parsers were broken when %defines was used together with "%define api.value.type union". *** Redeclarations are reported in proper order On %token FOO "foo" %printer {} "foo" %printer {} FOO bison used to report: foo.yy:2.10-11: error: %printer redeclaration for FOO %printer {} "foo" ^^ foo.yy:3.10-11: previous declaration %printer {} FOO ^^ Now, the "previous" declaration is always the first one. ** Documentation Bison now installs various files in its docdir (which defaults to '/usr/local/share/doc/bison'), including the three fully blown examples extracted from the documentation: - rpcalc Reverse Polish Calculator, a simple introductory example. - mfcalc Multi-function Calc, a calculator with memory and functions and located error messages. - calc++ a calculator in C++ using variant support and token constructors. * Noteworthy changes in release 3.0.2 (2013-12-05) [stable] ** Bug fixes *** Generated source files when errors are reported When warnings are issued and -Werror is set, bison would still generate the source files (*.c, *.h...). As a consequence, some runs of "make" could fail the first time, but not the second (as the files were generated anyway). This is fixed: bison no longer generates this source files, but, of course, still produces the various reports (*.output, *.xml, etc.). *** %empty is used in reports Empty right-hand sides are denoted by '%empty' in all the reports (text, dot, XML and formats derived from it). *** YYERROR and variants When C++ variant support is enabled, an error triggered via YYERROR, but not caught via error recovery, resulted in a double deletion. * Noteworthy changes in release 3.0.1 (2013-11-12) [stable] ** Bug fixes *** Errors in caret diagnostics On some platforms, some errors could result in endless diagnostics. *** Fixes of the -Werror option Options such as "-Werror -Wno-error=foo" were still turning "foo" diagnostics into errors instead of warnings. This is fixed. Actually, for consistency with GCC, "-Wno-error=foo -Werror" now also leaves "foo" diagnostics as warnings. Similarly, with "-Werror=foo -Wno-error", "foo" diagnostics are now errors. *** GLR Predicates As demonstrated in the documentation, one can now leave spaces between "%?" and its "{". *** Installation The yacc.1 man page is no longer installed if --disable-yacc was specified. *** Fixes in the test suite Bugs and portability issues. * Noteworthy changes in release 3.0 (2013-07-25) [stable] ** WARNING: Future backward-incompatibilities! Like other GNU packages, Bison will start using some of the C99 features for its own code, especially the definition of variables after statements. The generated C parsers still aim at C90. ** Backward incompatible changes *** Obsolete features Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR. Support for yystype and yyltype is removed (deprecated in Bison 1.875): use YYSTYPE and YYLTYPE. Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison 1.875): use %lex-param, %parse-param, or %param. Missing semicolons at the end of actions are no longer added (as announced in the release 2.5). *** Use of YACC='bison -y' TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use Bison extensions. Traditional Yacc generates 'y.tab.c' whatever the name of the input file. Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly 'y.tab.h' and 'y.output') to be generated from 'foo.y'. To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an implementation of Yacc, was using Bison as 'bison -y'. While it does ensure compatible output file names, it also enables warnings for incompatibilities with POSIX Yacc. In other words, 'bison -y' triggers warnings for Bison extensions. Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c' (which also generates 'y.tab.h' and 'y.output' when needed). Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc flags (YFLAGS, or AM_YFLAGS with Automake). ** Bug fixes *** The epilogue is no longer affected by internal #defines (glr.c) The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in generated code. These weren't properly undefined before the inclusion of the user epilogue, so functions such as the following were butchered by the preprocessor expansion: int yylex (YYSTYPE *yylval); This is fixed: yylval, yynerrs, yychar, and yylloc are now valid identifiers for user-provided variables. *** stdio.h is no longer needed when locations are enabled (yacc.c) Changes in Bison 2.7 introduced a dependency on FILE and fprintf when locations are enabled. This is fixed. *** Warnings about useless %pure-parser/%define api.pure are restored ** Diagnostics reported by Bison Most of these features were contributed by Théophile Ranquet and Victor Santet. *** Carets Version 2.7 introduced caret errors, for a prettier output. These are now activated by default. The old format can still be used by invoking Bison with -fno-caret (or -fnone). Some error messages that reproduced excerpts of the grammar are now using the caret information only. For instance on: %% exp: 'a' | 'a'; Bison 2.7 reports: in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr] in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother] Now bison reports: in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr] in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother] exp: 'a' | 'a'; ^^^ and "bison -fno-caret" reports: in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr] in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother] *** Enhancements of the -Werror option The -Werror=CATEGORY option is now recognized, and will treat specified warnings as errors. The warnings need not have been explicitly activated using the -W option, this is similar to what GCC 4.7 does. For example, given the following command line, Bison will treat both warnings related to POSIX Yacc incompatibilities and S/R conflicts as errors (and only those): $ bison -Werror=yacc,error=conflicts-sr input.y If no categories are specified, -Werror will make all active warnings into errors. For example, the following line does the same the previous example: $ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y (By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.) Note that the categories in this -Werror option may not be prefixed with "no-". However, -Wno-error[=CATEGORY] is valid. Note that -y enables -Werror=yacc. Therefore it is now possible to require Yacc-like behavior (e.g., always generate y.tab.c), but to report incompatibilities as warnings: "-y -Wno-error=yacc". *** The display of warnings is now richer The option that controls a given warning is now displayed: foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother] In the case of warnings treated as errors, the prefix is changed from "warning: " to "error: ", and the suffix is displayed, in a manner similar to GCC, as [-Werror=CATEGORY]. For instance, where the previous version of Bison would report (and exit with failure): bison: warnings being treated as errors input.y:1.1: warning: stray ',' treated as white space it now reports: input.y:1.1: error: stray ',' treated as white space [-Werror=other] *** Deprecated constructs The new 'deprecated' warning category flags obsolete constructs whose support will be discontinued. It is enabled by default. These warnings used to be reported as 'other' warnings. *** Useless semantic types Bison now warns about useless (uninhabited) semantic types. Since semantic types are not declared to Bison (they are defined in the opaque %union structure), it is %printer/%destructor directives about useless types that trigger the warning: %token <type1> term %type <type2> nterm %printer {} <type1> <type3> %destructor {} <type2> <type4> %% nterm: term { $$ = $1; }; 3.28-34: warning: type <type3> is used, but is not associated to any symbol 4.28-34: warning: type <type4> is used, but is not associated to any symbol *** Undefined but unused symbols Bison used to raise an error for undefined symbols that are not used in the grammar. This is now only a warning. %printer {} symbol1 %destructor {} symbol2 %type <type> symbol3 %% exp: "a"; *** Useless destructors or printers Bison now warns about useless destructors or printers. In the following example, the printer for <type1>, and the destructor for <type2> are useless: all symbols of <type1> (token1) already have a printer, and all symbols of type <type2> (token2) already have a destructor. %token <type1> token1 <type2> token2 <type3> token3 <type4> token4 %printer {} token1 <type1> <type3> %destructor {} token2 <type2> <type4> *** Conflicts The warnings and error messages about shift/reduce and reduce/reduce conflicts have been normalized. For instance on the following foo.y file: %glr-parser %% exp: exp '+' exp | '0' | '0'; compare the previous version of bison: $ bison foo.y foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce $ bison -Werror foo.y bison: warnings being treated as errors foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce with the new behavior: $ bison foo.y foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr] foo.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr] $ bison -Werror foo.y foo.y: error: 1 shift/reduce conflict [-Werror=conflicts-sr] foo.y: error: 2 reduce/reduce conflicts [-Werror=conflicts-rr] When %expect or %expect-rr is used, such as with bar.y: %expect 0 %glr-parser %% exp: exp '+' exp | '0' | '0'; Former behavior: $ bison bar.y bar.y: conflicts: 1 shift/reduce, 2 reduce/reduce bar.y: expected 0 shift/reduce conflicts bar.y: expected 0 reduce/reduce conflicts New one: $ bison bar.y bar.y: error: shift/reduce conflicts: 1 found, 0 expected bar.y: error: reduce/reduce conflicts: 2 found, 0 expected ** Incompatibilities with POSIX Yacc The 'yacc' category is no longer part of '-Wall', enable it explicitly with '-Wyacc'. ** Additional yylex/yyparse arguments The new directive %param declares additional arguments to both yylex and yyparse. The %lex-param, %parse-param, and %param directives support one or more arguments. Instead of %lex-param {arg1_type *arg1} %lex-param {arg2_type *arg2} %parse-param {arg1_type *arg1} %parse-param {arg2_type *arg2} one may now declare %param {arg1_type *arg1} {arg2_type *arg2} ** Types of values for %define variables Bison used to make no difference between '%define foo bar' and '%define foo "bar"'. The former is now called a 'keyword value', and the latter a 'string value'. A third kind was added: 'code values', such as '%define foo {bar}'. Keyword variables are used for fixed value sets, e.g., %define lr.type lalr Code variables are used for value in the target language, e.g., %define api.value.type {struct semantic_type} String variables are used remaining cases, e.g. file names. ** Variable api.token.prefix The variable api.token.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.token.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.value.type This new %define variable supersedes the #define macro YYSTYPE. The use of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either using %union or %defining api.value.type results in undefined behavior. Either define api.value.type, or use "%union": %union { int ival; char *sval; } %token <ival> INT "integer" %token <sval> STRING "string" %printer { fprintf (yyo, "%d", $$); } <ival> %destructor { free ($$); } <sval> /* In yylex(). */ yylval.ival = 42; return INT; yylval.sval = "42"; return STRING; The %define variable api.value.type supports both keyword and code values. The keyword value 'union' means that the user provides genuine types, not union member names such as "ival" and "sval" above (WARNING: will fail if -y/--yacc/%yacc is enabled). %define api.value.type union %token <int> INT "integer" %token <char *> STRING "string" %printer { fprintf (yyo, "%d", $$); } <int> %destructor { free ($$); } <char *> /* In yylex(). */ yylval.INT = 42; return INT; yylval.STRING = "42"; return STRING; The keyword value variant is somewhat equivalent, but for C++ special provision is made to allow classes to be used (more about this below). %define api.value.type variant %token <int> INT "integer" %token <std::string> STRING "string" Code values (in braces) denote user defined types. This is where YYSTYPE used to be used. %code requires { struct my_value { enum { is_int, is_string } kind; union { int ival; char *sval; } u; }; } %define api.value.type {struct my_value} %token <u.ival> INT "integer" %token <u.sval> STRING "string" %printer { fprintf (yyo, "%d", $$); } <u.ival> %destructor { free ($$); } <u.sval> /* In yylex(). */ yylval.u.ival = 42; return INT; yylval.u.sval = "42"; return STRING; ** Variable parse.error This variable controls the verbosity of error messages. The use of the %error-verbose directive is deprecated in favor of "%define parse.error verbose". ** Deprecated %define variable names The following variables have been renamed for consistency. Backward compatibility is ensured, but upgrading is recommended. lr.default-reductions -> lr.default-reduction lr.keep-unreachable-states -> lr.keep-unreachable-state namespace -> api.namespace stype -> api.value.type ** Semantic predicates Contributed by Paul Hilfinger. The new, experimental, semantic-predicate feature allows actions of the form "%?{ BOOLEAN-EXPRESSION }", which cause syntax errors (as for YYERROR) if the expression evaluates to 0, and are evaluated immediately in GLR parsers, rather than being deferred. The result is that they allow the programmer to prune possible parses based on the values of run-time expressions. ** The directive %expect-rr is now an error in non GLR mode It used to be an error only if used in non GLR mode, _and_ if there are reduce/reduce conflicts. ** Tokens are numbered in their order of appearance Contributed by Valentin Tolmer. With '%token A B', A had a number less than the one of B. However, precedence declarations used to generate a reversed order. This is now fixed, and introducing tokens with any of %token, %left, %right, %precedence, or %nonassoc yields the same result. When mixing declarations of tokens with a literal character (e.g., 'a') or with an identifier (e.g., B) in a precedence declaration, Bison numbered the literal characters first. For example %right A B 'c' 'd' would lead to the tokens declared in this order: 'c' 'd' A B. Again, the input order is now preserved. These changes were made so that one can remove useless precedence and associativity declarations (i.e., map %nonassoc, %left or %right to %precedence, or to %token) and get exactly the same output. ** Useless precedence and associativity Contributed by Valentin Tolmer. When developing and maintaining a grammar, useless associativity and precedence directives are common. They can be a nuisance: new ambiguities arising are sometimes masked because their conflicts are resolved due to the extra precedence or associativity information. Furthermore, it can hinder the comprehension of a new grammar: one will wonder about the role of a precedence, where in fact it is useless. The following changes aim at detecting and reporting these extra directives. *** Precedence warning category A new category of warning, -Wprecedence, was introduced. It flags the useless precedence and associativity directives. *** Useless associativity Bison now warns about symbols with a declared associativity that is never used to resolve conflicts. In that case, using %precedence is sufficient; the parsing tables will remain unchanged. Solving these warnings may raise useless precedence warnings, as the symbols no longer have associativity. For example: %left '+' %left '*' %% exp: "number" | exp '+' "number" | exp '*' exp ; will produce a warning: useless associativity for '+', use %precedence [-Wprecedence] %left '+' ^^^ *** Useless precedence Bison now warns about symbols with a declared precedence and no declared associativity (i.e., declared with %precedence), and whose precedence is never used. In that case, the symbol can be safely declared with %token instead, without modifying the parsing tables. For example: %precedence '=' %% exp: "var" '=' "number"; will produce a warning: useless precedence for '=' [-Wprecedence] %precedence '=' ^^^ *** Useless precedence and associativity In case of both useless precedence and associativity, the issue is flagged as follows: %nonassoc '=' %% exp: "var" '=' "number"; The warning is: warning: useless precedence and associativity for '=' [-Wprecedence] %nonassoc '=' ^^^ ** Empty rules With help from Joel E. Denny and Gabriel Rassoul. Empty rules (i.e., with an empty right-hand side) can now be explicitly marked by the new %empty directive. Using %empty on a non-empty rule is an error. The new -Wempty-rule warning reports empty rules without %empty. On the following grammar: %% s: a b c; a: ; b: %empty; c: 'a' %empty; bison reports: 3.4-5: warning: empty rule without %empty [-Wempty-rule] a: {} ^^ 5.8-13: error: %empty on non-empty rule c: 'a' %empty {}; ^^^^^^ ** 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". Contributed by Paolo Bonzini. The Java skeleton now supports push parsing. Contributed by Dennis Heimbigner. ** C++ skeletons improvements *** The parser header is no longer mandatory (lalr1.cc, glr.cc) Using %defines is now optional. Without it, the needed support classes are defined in the generated parser, instead of additional files (such as location.hh, position.hh and stack.hh). *** Locations are no longer mandatory (lalr1.cc, glr.cc) Both lalr1.cc and glr.cc no longer require %location. *** syntax_error exception (lalr1.cc) The C++ parser features a syntax_error exception, which can be thrown from the scanner or from user rules to raise syntax errors. This facilitates reporting errors caught in sub-functions (e.g., rejecting too large integral literals from a conversion function used by the scanner, or rejecting invalid combinations from a factory invoked by the user actions). *** %define api.value.type variant This is based on a submission from Michiel De Wilde. With help from Théophile Ranquet. In this mode, complex C++ objects can be used as semantic values. For instance: %token <::std::string> TEXT; %token <int> NUMBER; %token SEMICOLON ";" %type <::std::string> item; %type <::std::list<std::string>> list; %% result: list { std::cout << $1 << std::endl; } ; list: %empty { /* Generates an empty string list. */ } | list item ";" { std::swap ($$, $1); $$.push_back ($2); } ; item: TEXT { std::swap ($$, $1); } | NUMBER { $$ = string_cast ($1); } ; *** %define api.token.constructor When variants are enabled, Bison can generate functions to build the tokens. This guarantees that the token type (e.g., NUMBER) is consistent with the semantic value (e.g., int): parser::symbol_type yylex () { parser::location_type loc = ...; ... return parser::make_TEXT ("Hello, world!", loc); ... return parser::make_NUMBER (42, loc); ... return parser::make_SEMICOLON (loc); ... } *** C++ locations There are operator- and operator-= for 'location'. Negative line/column increments can no longer underflow the resulting value. * Noteworthy changes in release 2.7.1 (2013-04-15) [stable] ** Bug fixes *** Fix compiler attribute portability (yacc.c) With locations enabled, __attribute__ was used unprotected. *** Fix some compiler warnings (lalr1.cc) * Noteworthy changes in release 2.7 (2012-12-12) [stable] ** Bug fixes Warnings about uninitialized yylloc in yyparse have been fixed. Restored C90 compliance (yet no report was ever made). ** Diagnostics are improved Contributed by Théophile Ranquet. *** Changes in the format of error messages This used to be the format of many error reports: input.y:2.7-12: %type redeclaration for exp input.y:1.7-12: previous declaration It is now: input.y:2.7-12: error: %type redeclaration for exp input.y:1.7-12: previous declaration *** New format for error reports: carets Caret errors have been added to Bison: input.y:2.7-12: error: %type redeclaration for exp %type <sval> exp ^^^^^^ input.y:1.7-12: previous declaration %type <ival> exp ^^^^^^ or input.y:3.20-23: error: ambiguous reference: '$exp' exp: exp '+' exp { $exp = $1 + $3; }; ^^^^ input.y:3.1-3: refers to: $exp at $$ exp: exp '+' exp { $exp = $1 + $3; }; ^^^ input.y:3.6-8: refers to: $exp at $1 exp: exp '+' exp { $exp = $1 + $3; }; ^^^ input.y:3.14-16: refers to: $exp at $3 exp: exp '+' exp { $exp = $1 + $3; }; ^^^ The default behavior for now is still not to display these unless explicitly asked with -fcaret (or -fall). However, in a later release, it will be made the default behavior (but may still be deactivated with -fno-caret). ** New value for %define variable: api.pure full The %define variable api.pure requests a pure (reentrant) parser. However, for historical reasons, using it in a location-tracking Yacc parser resulted in a yyerror function that did not take a location as a parameter. With this new value, the user may request a better pure parser, where yyerror does take a location as a parameter (in location-tracking parsers). The use of "%define api.pure true" is deprecated in favor of this new "%define api.pure full". ** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java) The %define variable api.location.type defines the name of the type to use for locations. When defined, Bison no longer generates the position.hh and location.hh files, nor does the parser will include them: the user is then responsible to define her type. This can be used in programs with several parsers to factor their location and position files: let one of them generate them, and the others just use them. This feature was actually introduced, but not documented, in Bison 2.5, under the name "location_type" (which is maintained for backward compatibility). For consistency, lalr1.java's %define variables location_type and position_type are deprecated in favor of api.location.type and api.position.type. ** Exception safety (lalr1.cc) The parse function now catches exceptions, uses the %destructors to release memory (the lookahead symbol and the symbols pushed on the stack) before re-throwing the exception. This feature is somewhat experimental. User feedback would be appreciated. ** Graph improvements in DOT and XSLT Contributed by Théophile Ranquet. The graphical presentation of the states is more readable: their shape is now rectangular, the state number is clearly displayed, and the items are numbered and left-justified. The reductions are now explicitly represented as transitions to other diamond shaped nodes. These changes are present in both --graph output and xml2dot.xsl XSLT processing, with minor (documented) differences. ** %language is no longer an experimental feature. The introduction of this feature, in 2.4, was four years ago. The --language option and the %language directive are no longer experimental. ** Documentation The sections about shift/reduce and reduce/reduce conflicts resolution have been fixed and extended. Although introduced more than four years ago, XML and Graphviz reports were not properly documented. The translation of midrule actions is now described. * Noteworthy changes in release 2.6.5 (2012-11-07) [stable] We consider compiler warnings about Bison generated parsers to be bugs. Rather than working around them in your own project, please consider reporting them to us. ** Bug fixes Warnings about uninitialized yylval and/or yylloc for push parsers with a pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to 3.2. Other issues in the test suite have been addressed. Null characters are correctly displayed in error messages. When possible, yylloc is correctly initialized before calling yylex. It is no longer necessary to initialize it in the %initial-action. * Noteworthy changes in release 2.6.4 (2012-10-23) [stable] Bison 2.6.3's --version was incorrect. This release fixes this issue. * Noteworthy changes in release 2.6.3 (2012-10-22) [stable] ** Bug fixes Bugs and portability issues in the test suite have been fixed. Some errors in translations have been addressed, and --help now directs users to the appropriate place to report them. Stray Info files shipped by accident are removed. Incorrect definitions of YY_, issued by yacc.c when no parser header is generated, are removed. All the generated headers are self-contained. ** Header guards (yacc.c, glr.c, glr.cc) In order to avoid collisions, the header guards are now YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>. For instance the header generated from %define api.prefix "calc" %defines "lib/parse.h" will use YY_CALC_LIB_PARSE_H_INCLUDED as guard. ** Fix compiler warnings in the generated parser (yacc.c, glr.c) The compilation of pure parsers (%define api.pure) can trigger GCC warnings such as: input.c: In function 'yyparse': input.c:1503:12: warning: 'yylval' may be used uninitialized in this function [-Wmaybe-uninitialized] *++yyvsp = yylval; ^ This is now fixed; pragmas to avoid these warnings are no longer needed. Warnings from clang ("equality comparison with extraneous parentheses" and "function declared 'noreturn' should not return") have also been addressed. * Noteworthy changes in release 2.6.2 (2012-08-03) [stable] ** Bug fixes Buffer overruns, complaints from Flex, and portability issues in the test suite have been fixed. ** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc) Trailing end-of-lines in %parse-param or %lex-param would result in invalid C++. This is fixed. ** Spurious spaces and end-of-lines The generated files no longer end (nor start) with empty lines. * Noteworthy changes in release 2.6.1 (2012-07-30) [stable] Bison no longer executes user-specified M4 code when processing a grammar. ** Future Changes In addition to the removal of the features announced in Bison 2.6, the next major release will remove the "Temporary hack for adding a semicolon to the user action", as announced in the release 2.5. Instead of: exp: exp "+" exp { $$ = $1 + $3 }; write: exp: exp "+" exp { $$ = $1 + $3; }; ** Bug fixes *** Type names are now properly escaped. *** glr.cc: set_debug_level and debug_level work as expected. *** Stray @ or $ in actions While Bison used to warn about stray $ or @ in action rules, it did not for other actions such as printers, destructors, or initial actions. It now does. ** Type names in actions For consistency with rule actions, it is now possible to qualify $$ by a type-name in destructors, printers, and initial actions. For instance: %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>; will display two values for each typed and untyped symbol (provided that YYSTYPE has both "ival" and "fval" fields). * Noteworthy changes in release 2.6 (2012-07-19) [stable] ** Future changes The next major release of Bison will drop support for the following deprecated features. Please report disagreements to bug-bison@gnu.org. *** K&R C parsers Support for generating parsers in K&R C will be removed. Parsers generated for C support ISO C90, and are tested with ISO C99 and ISO C11 compilers. *** Features deprecated since Bison 1.875 The definitions of yystype and yyltype will be removed; use YYSTYPE and YYLTYPE. YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and %lex-param, will no longer be supported. Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use %error-verbose. *** The generated header will be included (yacc.c) Instead of duplicating the content of the generated header (definition of YYSTYPE, yyparse declaration etc.), the generated parser will include it, as is already the case for GLR or C++ parsers. This change is deferred because existing versions of ylwrap (e.g., Automake 1.12.1) do not support it. ** Generated Parser Headers *** Guards (yacc.c, glr.c, glr.cc) The generated headers are now guarded, as is already the case for C++ parsers (lalr1.cc). For instance, with --defines=foo.h: #ifndef YY_FOO_H # define YY_FOO_H ... #endif /* !YY_FOO_H */ *** New declarations (yacc.c, glr.c) The generated header now declares yydebug and yyparse. Both honor --name-prefix=bar_, and yield int bar_parse (void); rather than #define yyparse bar_parse int yyparse (void); in order to facilitate the inclusion of several parser headers inside a single compilation unit. *** Exported symbols in C++ The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the header, are removed, as they prevent the possibility of including several generated headers from a single compilation unit. *** YYLSP_NEEDED For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no longer defined. ** New %define variable: api.prefix Now that the generated headers are more complete and properly protected against multiple inclusions, constant names, such as YYSTYPE are a problem. While yyparse and others are properly renamed by %name-prefix, YYSTYPE, YYDEBUG and others have never been affected by it. Because it would introduce backward compatibility issues in projects not expecting YYSTYPE to be renamed, instead of changing the behavior of %name-prefix, it is deprecated in favor of a new %define variable: api.prefix. The following examples compares both: %name-prefix "bar_" | %define api.prefix "bar_" %token <ival> FOO %token <ival> FOO %union { int ival; } %union { int ival; } %% %% exp: 'a'; exp: 'a'; bison generates: #ifndef BAR_FOO_H #ifndef BAR_FOO_H # define BAR_FOO_H # define BAR_FOO_H /* Enabling traces. */ /* Enabling traces. */ # ifndef YYDEBUG | # ifndef BAR_DEBUG > # if defined YYDEBUG > # if YYDEBUG > # define BAR_DEBUG 1 > # else > # define BAR_DEBUG 0 > # endif > # else # define YYDEBUG 0 | # define BAR_DEBUG 0 > # endif # endif | # endif # if YYDEBUG | # if BAR_DEBUG extern int bar_debug; extern int bar_debug; # endif # endif /* Tokens. */ /* Tokens. */ # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE # define YYTOKENTYPE | # define BAR_TOKENTYPE enum yytokentype { | enum bar_tokentype { FOO = 258 FOO = 258 }; }; # endif # endif #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \ && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED typedef union YYSTYPE | typedef union BAR_STYPE { { int ival; int ival; } YYSTYPE; | } BAR_STYPE; # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1 #endif #endif extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval; int bar_parse (void); int bar_parse (void); #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */ * Noteworthy changes in release 2.5.1 (2012-06-05) [stable] ** Future changes: The next major release will drop support for generating parsers in K&R C. ** yacc.c: YYBACKUP works as expected. ** glr.c improvements: *** Location support is eliminated when not requested: GLR parsers used to include location-related code even when locations were not requested, and therefore not even usable. *** __attribute__ is preserved: __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e., when -std is passed to GCC). ** lalr1.java: several fixes: The Java parser no longer throws ArrayIndexOutOfBoundsException if the first token leads to a syntax error. Some minor clean ups. ** Changes for C++: *** C++11 compatibility: C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L or higher. *** Header guards The header files such as "parser.hh", "location.hh", etc. used a constant name for preprocessor guards, for instance: #ifndef BISON_LOCATION_HH # define BISON_LOCATION_HH ... #endif // !BISON_LOCATION_HH The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower case characters are converted to upper case, and series of non-alphanumerical characters are converted to an underscore. With "bison -o lang++/parser.cc", "location.hh" would now include: #ifndef YY_LANG_LOCATION_HH # define YY_LANG_LOCATION_HH ... #endif // !YY_LANG_LOCATION_HH *** C++ locations: The position and location constructors (and their initialize methods) accept new arguments for line and column. Several issues in the documentation were fixed. ** liby is no longer asking for "rpl_fprintf" on some platforms. ** Changes in the manual: *** %printer is documented The "%printer" directive, supported since at least Bison 1.50, is finally documented. The "mfcalc" example is extended to demonstrate it. For consistency with the C skeletons, the C++ parsers now also support "yyoutput" (as an alias to "debug_stream ()"). *** Several improvements have been made: The layout for grammar excerpts was changed to a more compact scheme. Named references are motivated. The description of the automaton description file (*.output) is updated to the current format. Incorrect index entries were fixed. Some other errors were fixed. ** Building bison: *** Conflicting prototypes with recent/modified Flex. Fixed build problems with the current, unreleased, version of Flex, and some modified versions of 2.5.35, which have modified function prototypes. *** Warnings during the build procedure have been eliminated. *** Several portability problems in the test suite have been fixed: This includes warnings with some compilers, unexpected behavior of tools such as diff, warning messages from the test suite itself, etc. *** The install-pdf target works properly: Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer halts in the middle of its course. * Noteworthy changes in release 2.5 (2011-05-14) ** Grammar symbol names can now contain non-initial dashes: Consistently with directives (such as %error-verbose) and with %define variables (e.g. push-pull), grammar symbol names may contain dashes in any position except the beginning. This is a GNU extension over POSIX Yacc. Thus, use of this extension is reported by -Wyacc and rejected in Yacc mode (--yacc). ** Named references: Historically, Yacc and Bison have supported positional references ($n, $$) to allow access to symbol values from inside of semantic actions code. Starting from this version, Bison can also accept named references. When no ambiguity is possible, original symbol names may be used as named references: if_stmt : "if" cond_expr "then" then_stmt ';' { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); } In the more common case, explicit names may be declared: stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';' { $res = mk_if_stmt($cond, $then, $else); } Location information is also accessible using @name syntax. When accessing symbol names containing dots or dashes, explicit bracketing ($[sym.1]) must be used. These features are experimental in this version. More user feedback will help to stabilize them. Contributed by Alex Rozenman. ** IELR(1) and canonical LR(1): IELR(1) is a minimal LR(1) parser table generation algorithm. That is, given any context-free grammar, IELR(1) generates parser tables with the full language-recognition power of canonical LR(1) but with nearly the same number of parser states as LALR(1). This reduction in parser states is often an order of magnitude. More importantly, because canonical LR(1)'s extra parser states may contain duplicate conflicts in the case of non-LR(1) grammars, the number of conflicts for IELR(1) is often an order of magnitude less as well. This can significantly reduce the complexity of developing of a grammar. Bison can now generate IELR(1) and canonical LR(1) parser tables in place of its traditional LALR(1) parser tables, which remain the default. You can specify the type of parser tables in the grammar file with these directives: %define lr.type lalr %define lr.type ielr %define lr.type canonical-lr The default-reduction optimization in the parser tables can also be adjusted using "%define lr.default-reductions". For details on both of these features, see the new section "Tuning LR" in the Bison manual. These features are experimental. More user feedback will help to stabilize them. ** LAC (Lookahead Correction) for syntax error handling Contributed by Joel E. Denny. Canonical LR, IELR, and LALR can suffer from a couple of problems upon encountering a syntax error. First, the parser might perform additional parser stack reductions before discovering the syntax error. Such reductions can perform user semantic actions that are unexpected because they are based on an invalid token, and they cause error recovery to begin in a different syntactic context than the one in which the invalid token was encountered. Second, when verbose error messages are enabled (with %error-verbose or the obsolete "#define YYERROR_VERBOSE"), the expected token list in the syntax error message can both contain invalid tokens and omit valid tokens. The culprits for the above problems are %nonassoc, default reductions in inconsistent states, and parser state merging. Thus, IELR and LALR suffer the most. Canonical LR can suffer only if %nonassoc is used or if default reductions are enabled for inconsistent states. LAC is a new mechanism within the parsing algorithm that solves these problems for canonical LR, IELR, and LALR without sacrificing %nonassoc, default reductions, or state merging. When LAC is in use, canonical LR and IELR behave almost exactly the same for both syntactically acceptable and syntactically unacceptable input. While LALR still does not support the full language-recognition power of canonical LR and IELR, LAC at least enables LALR's syntax error handling to correctly reflect LALR's language-recognition power. Currently, LAC is only supported for deterministic parsers in C. You can enable LAC with the following directive: %define parse.lac full See the new section "LAC" in the Bison manual for additional details including a few caveats. LAC is an experimental feature. More user feedback will help to stabilize it. ** %define improvements: *** Can now be invoked via the command line: Each of these command-line options -D NAME[=VALUE] --define=NAME[=VALUE] -F NAME[=VALUE] --force-define=NAME[=VALUE] is equivalent to this grammar file declaration %define NAME ["VALUE"] except that the manner in which Bison processes multiple definitions for the same NAME differs. Most importantly, -F and --force-define quietly override %define, but -D and --define do not. For further details, see the section "Bison Options" in the Bison manual. *** Variables renamed: The following %define variables api.push_pull lr.keep_unreachable_states have been renamed to api.push-pull lr.keep-unreachable-states The old names are now deprecated but will be maintained indefinitely for backward compatibility. *** Values no longer need to be quoted in the grammar file: If a %define value is an identifier, it no longer needs to be placed within quotations marks. For example, %define api.push-pull "push" can be rewritten as %define api.push-pull push *** Unrecognized variables are now errors not warnings. *** Multiple invocations for any variable is now an error not a warning. ** Unrecognized %code qualifiers are now errors not warnings. ** Character literals not of length one: Previously, Bison quietly converted all character literals to length one. For example, without warning, Bison interpreted the operators in the following grammar to be the same token: exp: exp '++' | exp '+' exp ; Bison now warns when a character literal is not of length one. In some future release, Bison will start reporting an error instead. ** Destructor calls fixed for lookaheads altered in semantic actions: Previously for deterministic parsers in C, if a user semantic action altered yychar, the parser in some cases used the old yychar value to determine which destructor to call for the lookahead upon a syntax error or upon parser return. This bug has been fixed. ** C++ parsers use YYRHSLOC: Similarly to the C parsers, the C++ parsers now define the YYRHSLOC macro and use it in the default YYLLOC_DEFAULT. You are encouraged to use it. If, for instance, your location structure has "first" and "last" members, instead of # define YYLLOC_DEFAULT(Current, Rhs, N) \ do \ if (N) \ { \ (Current).first = (Rhs)[1].location.first; \ (Current).last = (Rhs)[N].location.last; \ } \ else \ { \ (Current).first = (Current).last = (Rhs)[0].location.last; \ } \ while (false) use: # define YYLLOC_DEFAULT(Current, Rhs, N) \ do \ if (N) \ { \ (Current).first = YYRHSLOC (Rhs, 1).first; \ (Current).last = YYRHSLOC (Rhs, N).last; \ } \ else \ { \ (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \ } \ while (false) ** YYLLOC_DEFAULT in C++: The default implementation of YYLLOC_DEFAULT used to be issued in the header file. It is now output in the implementation file, after the user %code sections so that its #ifndef guard does not try to override the user's YYLLOC_DEFAULT if provided. ** YYFAIL now produces warnings and Java parsers no longer implement it: YYFAIL has existed for many years as an undocumented feature of deterministic parsers in C generated by Bison. More recently, it was a documented feature of Bison's experimental Java parsers. As promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a semantic action now produces a deprecation warning, and Java parsers no longer implement YYFAIL at all. For further details, including a discussion of how to suppress C preprocessor warnings about YYFAIL being unused, see the Bison 2.4.2 NEWS entry. ** Temporary hack for adding a semicolon to the user action: Previously, Bison appended a semicolon to every user action for reductions when the output language defaulted to C (specifically, when neither %yacc, %language, %skeleton, or equivalent command-line options were specified). This allowed actions such as exp: exp "+" exp { $$ = $1 + $3 }; instead of exp: exp "+" exp { $$ = $1 + $3; }; As a first step in removing this misfeature, Bison now issues a warning when it appends a semicolon. Moreover, in cases where Bison cannot easily determine whether a semicolon is needed (for example, an action ending with a cpp directive or a braced compound initializer), it no longer appends one. Thus, the C compiler might now complain about a missing semicolon where it did not before. Future releases of Bison will cease to append semicolons entirely. ** Verbose syntax error message fixes: When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is specified, syntax error messages produced by the generated parser include the unexpected token as well as a list of expected tokens. The effect of %nonassoc on these verbose messages has been corrected in two ways, but a more complete fix requires LAC, described above: *** When %nonassoc is used, there can exist parser states that accept no tokens, and so the parser does not always require a lookahead token in order to detect a syntax error. Because no unexpected token or expected tokens can then be reported, the verbose syntax error message described above is suppressed, and the parser instead reports the simpler message, "syntax error". Previously, this suppression was sometimes erroneously triggered by %nonassoc when a lookahead was actually required. Now verbose messages are suppressed only when all previous lookaheads have already been shifted or discarded. *** Previously, the list of expected tokens erroneously included tokens that would actually induce a syntax error because conflicts for them were resolved with %nonassoc in the current parser state. Such tokens are now properly omitted from the list. *** Expected token lists are still often wrong due to state merging (from LALR or IELR) and default reductions, which can both add invalid tokens and subtract valid tokens. Canonical LR almost completely fixes this problem by eliminating state merging and default reductions. However, there is one minor problem left even when using canonical LR and even after the fixes above. That is, if the resolution of a conflict with %nonassoc appears in a later parser state than the one at which some syntax error is discovered, the conflicted token is still erroneously included in the expected token list. Bison's new LAC implementation, described above, eliminates this problem and the need for canonical LR. However, LAC is still experimental and is disabled by default. ** Java skeleton fixes: *** A location handling bug has been fixed. *** The top element of each of the value stack and location stack is now cleared when popped so that it can be garbage collected. *** Parser traces now print the top element of the stack. ** -W/--warnings fixes: *** Bison now properly recognizes the "no-" versions of categories: For example, given the following command line, Bison now enables all warnings except warnings for incompatibilities with POSIX Yacc: bison -Wall,no-yacc gram.y *** Bison now treats S/R and R/R conflicts like other warnings: Previously, conflict reports were independent of Bison's normal warning system. Now, Bison recognizes the warning categories "conflicts-sr" and "conflicts-rr". This change has important consequences for the -W and --warnings command-line options. For example: bison -Wno-conflicts-sr gram.y # S/R conflicts not reported bison -Wno-conflicts-rr gram.y # R/R conflicts not reported bison -Wnone gram.y # no conflicts are reported bison -Werror gram.y # any conflict is an error However, as before, if the %expect or %expect-rr directive is specified, an unexpected number of conflicts is an error, and an expected number of conflicts is not reported, so -W and --warning then have no effect on the conflict report. *** The "none" category no longer disables a preceding "error": For example, for the following command line, Bison now reports errors instead of warnings for incompatibilities with POSIX Yacc: bison -Werror,none,yacc gram.y *** The "none" category now disables all Bison warnings: Previously, the "none" category disabled only Bison warnings for which there existed a specific -W/--warning category. However, given the following command line, Bison is now guaranteed to suppress all warnings: bison -Wnone gram.y ** Precedence directives can now assign token number 0: Since Bison 2.3b, which restored the ability of precedence directives to assign token numbers, doing so for token number 0 has produced an assertion failure. For example: %left END 0 This bug has been fixed. * Noteworthy changes in release 2.4.3 (2010-08-05) ** Bison now obeys -Werror and --warnings=error for warnings about grammar rules that are useless in the parser due to conflicts. ** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have been fixed. ** Failures in the test suite for GCC 4.5 have been fixed. ** Failures in the test suite for some versions of Sun Studio C++ have been fixed. ** Contrary to Bison 2.4.2's NEWS entry, it has been decided that warnings about undefined %prec identifiers will not be converted to errors in Bison 2.5. They will remain warnings, which should be sufficient for POSIX while avoiding backward compatibility issues. ** Minor documentation fixes. * Noteworthy changes in release 2.4.2 (2010-03-20) ** Some portability problems that resulted in failures and livelocks in the test suite on some versions of at least Solaris, AIX, HP-UX, RHEL4, and Tru64 have been addressed. As a result, fatal Bison errors should no longer cause M4 to report a broken pipe on the affected platforms. ** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately. POSIX specifies that an error be reported for any identifier that does not appear on the LHS of a grammar rule and that is not defined by %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this error report for the case when an identifier appears only after a %prec directive. It is now restored. However, for backward compatibility with recent Bison releases, it is only a warning for now. In Bison 2.5 and later, it will return to being an error. [Between the 2.4.2 and 2.4.3 releases, it was decided that this warning will not be converted to an error in Bison 2.5.] ** Detection of GNU M4 1.4.6 or newer during configure is improved. ** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS, YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now avoided. ** %code is now a permanent feature. A traditional Yacc prologue directive is written in the form: %{CODE%} To provide a more flexible alternative, Bison 2.3b introduced the %code directive with the following forms for C/C++: %code {CODE} %code requires {CODE} %code provides {CODE} %code top {CODE} These forms are now considered permanent features of Bison. See the %code entries in the section "Bison Declaration Summary" in the Bison manual for a summary of their functionality. See the section "Prologue Alternatives" for a detailed discussion including the advantages of %code over the traditional Yacc prologue directive. Bison's Java feature as a whole including its current usage of %code is still considered experimental. ** YYFAIL is deprecated and will eventually be removed. YYFAIL has existed for many years as an undocumented feature of deterministic parsers in C generated by Bison. Previously, it was documented for Bison's experimental Java parsers. YYFAIL is no longer documented for Java parsers and is formally deprecated in both cases. Users are strongly encouraged to migrate to YYERROR, which is specified by POSIX. Like YYERROR, you can invoke YYFAIL from a semantic action in order to induce a syntax error. The most obvious difference from YYERROR is that YYFAIL will automatically invoke yyerror to report the syntax error so that you don't have to. However, there are several other subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is used. For a more detailed discussion, see: http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but deterministic parsers in C will continue to implement it. However, because YYFAIL is already flawed, it seems futile to try to make new Bison features compatible with it. Thus, during parser generation, Bison 2.5 will produce a warning whenever it discovers YYFAIL in a rule action. In a later release, YYFAIL will be disabled for %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will be removed altogether. There exists at least one case where Bison 2.5's YYFAIL warning will be a false positive. Some projects add phony uses of YYFAIL and other Bison-defined macros for the sole purpose of suppressing C preprocessor warnings (from GCC cpp's -Wunused-macros, for example). To avoid Bison's future warning, such YYFAIL uses can be moved to the epilogue (that is, after the second "%%") in the Bison input file. In this release (2.4.2), Bison already generates its own code to suppress C preprocessor warnings for YYFAIL, so projects can remove their own phony uses of YYFAIL if compatibility with Bison releases prior to 2.4.2 is not necessary. ** Internationalization. Fix a regression introduced in Bison 2.4: Under some circumstances, message translations were not installed although supported by the host system. * Noteworthy changes in release 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. * Noteworthy changes in release 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. * Noteworthy changes in release 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. Contributed by Paolo Bonzini. ** %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. Contributed by Wojciech Polak. ** 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 midrule values Since Bison 2.2, Bison has warned about midrule 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 midrule values that are used but not set. For example, Bison warns about unset $$ in the midrule action in: exp: '1' { $1 = 1; } '+' exp { $$ = $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 midrule value if that midrule value is not actually ever referenced using either $$ or $n in a semantic action. The default %destructor's and %printer's are experimental. More user feedback will help to determine whether they should become permanent features. See the section "Freeing Discarded Symbols" in the Bison manual for further details. ** %left, %right, and %nonassoc can now declare token numbers. This is required by POSIX. However, see the end of section "Operator Precedence" in the Bison manual for a caveat concerning the treatment of literal strings. ** The nonfunctional --no-parser, -n, and %no-parser options have been completely removed from Bison. * Noteworthy changes in release 2.3a (2006-09-13) ** Instead of %union, you can define and use your own union type YYSTYPE if your grammar contains at least one <type> tag. Your YYSTYPE need not be a macro; it can be a typedef. This change is for compatibility with other Yacc implementations, and is required by POSIX. ** Locations columns and lines start at 1. In accordance with the GNU Coding Standards and Emacs. ** You may now declare per-type and default %destructor's and %printer's: For example: %union { char *string; } %token <string> STRING1 %token <string> STRING2 %type <string> string1 %type <string> string2 %union { char character; } %token <character> CHR %type <character> chr %destructor { free ($$); } %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. * Noteworthy changes in release 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. * Noteworthy changes in release 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 midrule 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. * Noteworthy changes in release 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"'. * Noteworthy changes in release 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. * Noteworthy changes in release 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. ** %parse-param and %lex-param The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass additional context to yyparse and yylex. They suffer from several shortcomings: - a single argument only can be added, - their types are weak (void *), - this context is not passed to ancillary functions such as yyerror, - only yacc.c parsers support them. The new %parse-param/%lex-param directives provide a more precise control. For instance: %parse-param {int *nastiness} %lex-param {int *nastiness} %parse-param {int *randomness} results in the following signatures: int yylex (int *nastiness); int yyparse (int *nastiness, int *randomness); or, if both %pure-parser and %locations are used: int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness); int yyparse (int *nastiness, int *randomness); ** 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. * Noteworthy changes in release 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 midrule actions The following code: foo: { ... } { $$ = $1; } ... was incorrectly rejected: $1 is defined in the second midrule action, and is equal to the $$ of the first midrule action. * Noteworthy changes in release 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 midrule action, such as in: %type <foo> bar %% bar: '0' {} '0'; This is fixed. ** GNU M4 is now required when using Bison. * Noteworthy changes in release 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. * Noteworthy changes in release 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. * Noteworthy changes in release 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. * Noteworthy changes in release 1.32 (2002-01-23) ** Fix Yacc output file names ** Portability fixes ** Italian, Dutch translations * Noteworthy changes in release 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". * Noteworthy changes in release 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. * Noteworthy changes in release 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. * Noteworthy changes in release 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. * Noteworthy changes in release 1.27 ** The make rule which prevented bison.simple from being created on some systems has been fixed. * Noteworthy changes in release 1.26 ** Bison now uses Automake. ** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>. ** Token numbers now start at 257 as previously documented, not 258. ** Bison honors the TMPDIR environment variable. ** A couple of buffer overruns have been fixed. ** Problems when closing files should now be reported. ** Generated parsers should now work even on operating systems which do not provide alloca(). * Noteworthy changes in release 1.25 (1995-10-16) ** Errors in the input grammar are not fatal; Bison keeps reading the grammar file, and reports all the errors found in it. ** Tokens can now be specified as multiple-character strings: for example, you could use "<=" for a token which looks like <=, instead of choosing a name like LESSEQ. ** The %token_table declaration says to write a table of tokens (names and numbers) into the parser file. The yylex function can use this table to recognize multiple-character string tokens, or for other purposes. ** The %no_lines declaration says not to generate any #line preprocessor directives in the parser file. ** The %raw declaration says to use internal Bison token numbers, not Yacc-compatible token numbers, when token names are defined as macros. ** The --no-parser option produces the parser tables without including the parser engine; a project can now use its own parser engine. The actions go into a separate file called NAME.act, in the form of a switch statement body. * Noteworthy changes in release 1.23 The user can define YYPARSE_PARAM as the name of an argument to be passed into yyparse. The argument should have type void *. It should actually point to an object. Grammar actions can access the variable by casting it to the proper pointer type. Line numbers in output file corrected. * Noteworthy changes in release 1.22 --help option added. * Noteworthy changes in release 1.20 Output file does not redefine const for C++. ----- LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init LocalWords: TOK calc yyo fval Wconflicts parsers yystackp yyval yynerrs LocalWords: Théophile Ranquet Santet fno fnone stype associativity Tolmer LocalWords: Wprecedence Rassoul Wempty Paolo Bonzini parser's Michiel loc LocalWords: redeclaration sval fcaret reentrant XSLT xsl Wmaybe yyvsp Tedi LocalWords: pragmas noreturn untyped Rozenman unexpanded Wojciech Polak LocalWords: Alexandre MERCHANTABILITY yytype emplace ptr automove lvalues LocalWords: nonterminal yy args Pragma dereference yyformat rhs docdir bw LocalWords: Redeclarations rpcalc Autoconf YFLAGS Makefiles PROG DECL num LocalWords: Heimbigner AST src ast Makefile srcdir MinGW xxlex XXSTYPE LocalWords: XXLTYPE strictfp IDEs ffixit fdiagnostics parseable fixits LocalWords: Wdeprecated yytext Variadic variadic yyrhs yyphrs RCS README LocalWords: noexcept constexpr ispell american deprecations backend Teoh LocalWords: YYPRINT Mangold Bonzini's Wdangling exVal baz checkable gcc LocalWords: fsanitize Vogelsgesang lis redeclared stdint automata yytname LocalWords: yysymbol yytnamerr yyreport ctx ARGMAX yysyntax stderr LPAREN LocalWords: symrec yypcontext TOKENMAX yyexpected YYEMPTY yypstate YYEOF LocalWords: autocompletion bistromathic submessages Cayuela lexcalc hoc LocalWords: yytoken YYUNDEF YYerror basename Automake's UTF ifdef ffile LocalWords: gotos readline Imbimbo Wcounterexamples Wcex Nonunifying rcex Local Variables: ispell-dictionary: "american" mode: outline fill-column: 76 End: Copyright (C) 1995-2015, 2018-2020 Free Software Foundation, Inc. This file is part of Bison, the GNU Parser Generator. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the "GNU Free Documentation License" file as part of this distribution.
