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bison 2.0 主要可以用来做语法分析用的

Bison News
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Changes in version 2.0, 2004-12-25:

* Possibly-incompatible changes

  - Bison-generated parsers no longer default to using the alloca function
    (when available) to extend the parser stack, due to widespread
    problems in unchecked stack-overflow detection.  You can "#define
    YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
    the manual to determine safe values for YYMAXDEPTH in that case.

  - Error token location.
    During error recovery, the location of the syntax error is updated
    to cover the whole sequence covered by the error token: it includes
    the shifted symbols thrown away during the first part of the error
    recovery, and the lookahead rejected during the second part.

  - Semicolon changes:
    . Stray semicolons are no longer allowed at the start of a grammar.
    . Semicolons are now required after in-grammar declarations.

  - Unescaped newlines are no longer allowed in character constants or
    string literals.  They were never portable, and GCC 3.4.0 has
    dropped support for them.  Better diagnostics are now generated if
    forget a closing quote.

  - NUL bytes are no longer allowed in Bison string literals, unfortunately.

* New features

  - GLR grammars now support locations.

  - New directive: %initial-action.
    This directive allows the user to run arbitrary code (including
    initializing @$) from yyparse before parsing starts.

  - A new directive "%expect-rr N" specifies the expected number of
    reduce/reduce conflicts in GLR parsers.

  - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
    This is a GNU extension.

  - The option `--report=lookahead' was changed to `--report=look-ahead'.
    The old spelling still works, but is not documented and will be
    removed.

  - Experimental %destructor support has been added to lalr1.cc.

  - New configure option --disable-yacc, to disable installation of the
    yacc command and -ly library introduced in 1.875 for POSIX conformance.

* Bug fixes

  - For now, %expect-count violations are now just warnings, not errors.
    This is for compatibility with Bison 1.75 and earlier (when there are
    reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
    are too many or too few shift/reduce conflicts).  However, in future
    versions of Bison we plan to improve the %expect machinery so that
    these violations will become errors again.

  - Within Bison itself, numbers (e.g., goto numbers) are no longer
    arbitrarily limited to 16-bit counts.

  - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.

Changes in version 1.875, 2003-01-01:

* The documentation license has been upgraded to version 1.2
  of the GNU Free Documentation License.

* syntax error processing

  - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
    locations too.  This fixes bugs in error-location computation.

  - %destructor
    It is now possible to reclaim the memory associated to symbols
    discarded during error recovery.  This feature is still experimental.

  - %error-verbose
    This new directive is preferred over YYERROR_VERBOSE.

  - #defining yyerror to steal internal variables is discouraged.
    It is not guaranteed to work forever.

* POSIX conformance

  - Semicolons are once again optional at the end of grammar rules.
    This reverts to the behavior of Bison 1.33 and earlier, and improves
    compatibility with Yacc.

  - `parse error' -> `syntax error'
    Bison now uniformly uses the term `syntax error'; formerly, the code
    and manual sometimes used the term `parse error' instead.  POSIX
    requires `syntax error' in diagnostics, and it was thought better to
    be consistent.

  - The documentation now emphasizes that yylex and yyerror must be
    declared before use.  C99 requires this.

  - Bison now parses C99 lexical constructs like UCNs and
    backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.

  - File names are properly escaped in C output.  E.g., foo\bar.y is
    output as "foo\\bar.y".

  - Yacc command and library now available
    The Bison distribution now installs a `yacc' command, as POSIX requires.
    Also, Bison now installs a small library liby.a containing
    implementations of Yacc-compatible yyerror and main functions.
    This library is normally not useful, but POSIX requires it.

  - Type clashes now generate warnings, not errors.

  - If the user does not define YYSTYPE as a macro, Bison now declares it
    using typedef instead of defining it as a macro.
    For consistency, YYLTYPE is also declared instead of defined.

* Other compatibility issues

  - %union directives can now have a tag before the `{', e.g., the
    directive `%union foo {...}' now generates the C code
    `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
    The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
    For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
    This is for compatibility with both Yacc and Bison 1.35.

  - `;' is output before the terminating `}' of an action, for
    compatibility with Bison 1.35.

  - Bison now uses a Yacc-style format for conflict reports, e.g.,
    `conflicts: 2 shift/reduce, 1 reduce/reduce'.

  - `yystype' and `yyltype' are now obsolescent macros instead of being
    typedefs or tags; they are no longer documented and are planned to be
    withdrawn in a future release.

* GLR parser notes

  - GLR and inline
    Users of Bison have to decide how they handle the portability of the
    C keyword `inline'.

  - `parsing stack overflow...' -> `parser stack overflow'
    GLR parsers now report `parser stack overflow' as per the Bison manual.

* Bison now warns if it detects conflicting outputs to the same file,
  e.g., it generates a warning for `bison -d -o foo.h foo.y' since
  that command outputs both code and header to foo.h.

* #line in output files
  - --no-line works properly.

* Bison can no longer be built by a K&R C compiler; it requires C89 or
  later to be built.  This change originally took place a few versions
  ago, but nobody noticed until we recently asked someone to try
  building Bison with a K&R C compiler.

Changes in version 1.75, 2002-10-14:

* Bison should now work on 64-bit hosts.

* Indonesian translation thanks to Tedi Heriyanto.

* GLR parsers
  Fix spurious parse errors.

* Pure parsers
  Some people redefine yyerror to steal yyparse' private variables.
  Reenable this trick until an official feature replaces it.

* Type Clashes
  In agreement with POSIX and with other Yaccs, leaving a default
  action is valid when $$ is untyped, and $1 typed:

	untyped: ... typed;

  but the converse remains an error:

	typed: ... untyped;

* Values of mid-rule actions
  The following code:

	foo: { ... } { $$ = $1; } ...

  was incorrectly rejected: $1 is defined in the second mid-rule
  action, and is equal to the $$ of the first mid-rule action.

Changes in version 1.50, 2002-10-04:

* GLR parsing
  The declaration
     %glr-parser
  causes Bison to produce a Generalized LR (GLR) parser, capable of handling
  almost any context-free grammar, ambiguous or not.  The new declarations
  %dprec and %merge on grammar rules allow parse-time resolution of
  ambiguities.  Contributed by Paul Hilfinger.

  Unfortunately Bison 1.50 does not work properly on 64-bit hosts
  like the Alpha, so please stick to 32-bit hosts for now.

* Output Directory
  When not in Yacc compatibility mode, when the output file was not
  specified, running `bison foo/bar.y' created `foo/bar.c'.  It
  now creates `bar.c'.

* Undefined token
  The undefined token was systematically mapped to 2 which prevented
  the use of 2 by the user.  This is no longer the case.

* Unknown token numbers
  If yylex returned an out of range value, yyparse could die.  This is
  no longer the case.

* Error token
  According to POSIX, the error token must be 256.
  Bison extends this requirement by making it a preference: *if* the
  user specified that one of her tokens is numbered 256, then error
  will be mapped onto another number.

* Verbose error messages
  They no longer report `..., expecting error or...' for states where
  error recovery is possible.

* End token
  Defaults to `$end' instead of `$'.

* Error recovery now conforms to documentation and to POSIX
  When a Bison-generated parser encounters a syntax error, it now pops
  the stack until it finds a state that allows shifting the error
  token.  Formerly, it popped the stack until it found a state that
  allowed some non-error action other than a default reduction on the
  error token.  The new behavior has long been the documented behavior,
  and has long been required by POSIX.  For more details, please see
  Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
  <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.

* Traces
  Popped tokens and nonterminals are now reported.

* Larger grammars
  Larger grammars are now supported (larger token numbers, larger grammar
  size (= sum of the LHS and RHS lengths), larger LALR tables).
  Formerly, many of these numbers ran afoul of 16-bit limits;
  now these limits are 32 bits on most hosts.

* Explicit initial rule
  Bison used to play hacks with the initial rule, which the user does
  not write.  It is now explicit, and visible in the reports and
  graphs as rule 0.

* Useless rules
  Before, Bison reported the useless rules, but, although not used,
  included them in the parsers.  They are now actually removed.

* Useless rules, useless nonterminals
  They are now reported, as a warning, with their locations.

* Rules never reduced
  Rules that can never be reduced because of conflicts are now
  reported.

* Incorrect `Token not used'
  On a grammar such as

           %token useless useful
           %%
           exp: '0' %prec useful;

  where a token was used to set the precedence of the last rule,
  bison reported both `useful' and `useless' as useless tokens.

* Revert the C++ namespace changes introduced in 1.31
  as they caused too many portability hassles.

* Default locations
  By an accident of design, the default computation of @$ was
  performed after another default computation was performed: @$ = @1.
  The latter is now removed: YYLLOC_DEFAULT is fully responsible of
  the computation of @$.

* Token end-of-file
  The token end of file may be specified by the user, in which case,
  the user symbol is used in the reports, the graphs, and the verbose
  error messages instead of `$end', which remains being the default.
  For instance
     %token MYEOF 0
  or
     %token MYEOF 0 "end of file"

* Semantic parser
  This old option, which has been broken for ages, is removed.

* New translations
  Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
  Croatian, thanks to Denis Lackovic.

* Incorrect token definitions
  When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.

* Token definitions as enums
  Tokens are output both as the traditional #define's, and, provided
  the compiler supports ANSI C or is a C++ compiler, as enums.
  This lets debuggers display names instead of integers.