--*- outline -*-
-
* Short term
-** Use syntax_error from the scanner?
-This would provide a means to raise syntax error from function called
-from the scanner. Actually, there is no good solution to report a
-lexical error in general. Usually they are kept at the scanner level
-only, ignoring the guilty token. But that might not be the best bet,
-since we don't benefit from the syntactic error recovery.
-
-We still have the possibility to return an invalid token number, which
-does the trick. But then the error message from the parser is poor
-(something like "unexpected $undefined"). Since the scanner probably
-already reported the error, we should directly enter error-recovery,
-without reporting the error message (i.e., YYERROR's semantics).
-
-Back to lalr1.cc (whose name is now quite unfortunate, since it also
-covers lr and ielr), if we support exceptions from yylex, should we
-propose a lexical_error in addition to syntax_error? Should they have
-a common root, say parse_error? Should syntax_error be renamed
-syntactic_error for consistency with lexical_error?
-
-** Variable names.
-What should we name `variant' and `lex_symbol'?
-
-** Use b4_symbol in all the skeleton
-Then remove the older system, including the tables generated by
-output.c
-
-** Update the documentation on gnu.org
+** Graphviz display code thoughts
+The code for the --graph option is over two files: print_graph, and
+graphviz. This is because Bison used to also produce VCG graphs, but since
+this is no longer true, maybe we could consider these files for fusion.
+
+An other consideration worth noting is that print_graph.c (correct me if I
+am wrong) should contain generic functions, whereas graphviz.c and other
+potential files should contain just the specific code for that output
+format. It will probably prove difficult to tell if the implementation is
+actually generic whilst only having support for a single format, but it
+would be nice to keep stuff a bit tidier: right now, the construction of the
+bitset used to show reductions is in the graphviz-specific code, and on the
+opposite side we have some use of \l, which is graphviz-specific, in what
+should be generic code.
+
+Little effort seems to have been given to factoring these files and their
+rint{,-xml} counterpart. We would very much like to re-use the pretty format
+of states from .output for the graphs, etc.
+
+Also, the underscore in print_graph.[ch] isn't very fitting considering the
+dashes in the other filenames.
+
+Since graphviz dies on medium-to-big grammars, maybe consider an other tool?
+
+** push-parser
+Check it too when checking the different kinds of parsers. And be
+sure to check that the initial-action is performed once per parsing.
+
+** m4 names
+b4_shared_declarations is no longer what it is. Make it
+b4_parser_declaration for instance.
+
+** yychar in lalr1.cc
+There is a large difference bw maint and master on the handling of
+yychar (which was removed in lalr1.cc). See what needs to be
+back-ported.
+
+
+ /* User semantic actions sometimes alter yychar, and that requires
+ that yytoken be updated with the new translation. We take the
+ approach of translating immediately before every use of yytoken.
+ One alternative is translating here after every semantic action,
+ but that translation would be missed if the semantic action
+ invokes YYABORT, YYACCEPT, or YYERROR immediately after altering
+ yychar. In the case of YYABORT or YYACCEPT, an incorrect
+ destructor might then be invoked immediately. In the case of
+ YYERROR, subsequent parser actions might lead to an incorrect
+ destructor call or verbose syntax error message before the
+ lookahead is translated. */
+
+ /* Make sure we have latest lookahead translation. See comments at
+ user semantic actions for why this is necessary. */
+ yytoken = yytranslate_ (yychar);
+
+
+** stack.hh
+Get rid of it. The original idea is nice, but actually it makes
+the code harder to follow, and uselessly different from the other
+skeletons.
** Get rid of fake #lines [Bison: ...]
Possibly as simple as checking whether the column number is nonnegative.
** Rename LR0.cc
as lr0.cc, why upper case?
-** bench several bisons.
-Enhance bench.pl with %b to run different bisons.
-
-** Use b4_symbol everywhere.
-Move its definition in the more standard places and deploy it in other
-skeletons.
-
* Various
-** YYPRINT
-glr.c inherits its symbol_print function from c.m4, which supports
-YYPRINT. But to use YYPRINT yytoknum is needed, which not defined by
-glr.c.
-
-Anyway, IMHO YYPRINT is obsolete and should be restricted to yacc.c.
-
** YYERRCODE
Defined to 256, but not used, not documented. Probably the token
number for the error token, which POSIX wants to be 256, but which
"\"end of command\"", "error", "$undefined", "\"=\"", "\"break\"",
-** YYFAIL
-It is seems to be *really* obsolete now, shall we remove it?
-
-** YYBACKUP
-There is no test about it, no examples in the doc, and I'm not sure
-what it should look like. For instance what follows crashes.
-
- %error-verbose
- %debug
- %pure-parser
- %code {
- # include <stdio.h>
- # include <stdlib.h>
- # include <assert.h>
-
- static void yyerror (const char *msg);
- static int yylex (YYSTYPE *yylval);
- }
- %%
- exp:
- 'a' { printf ("a: %d\n", $1); }
- | 'b' { YYBACKUP('a', 123); }
- ;
- %%
- static int
- yylex (YYSTYPE *yylval)
- {
- static char const input[] = "b";
- static size_t toknum;
- assert (toknum < sizeof input);
- *yylval = (toknum + 1) * 10;
- return input[toknum++];
- }
-
- static void
- yyerror (const char *msg)
- {
- fprintf (stderr, "%s\n", msg);
- }
-
- int
- main (void)
- {
- yydebug = !!getenv("YYDEBUG");
- return yyparse ();
- }
-
** yychar == yyempty_
The code in yyerrlab reads:
if (yychar <= YYEOF)
- {
- /* Return failure if at end of input. */
- if (yychar == YYEOF)
- YYABORT;
- }
+ {
+ /* Return failure if at end of input. */
+ if (yychar == YYEOF)
+ YYABORT;
+ }
There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF.
But I can't produce the situation where yychar is YYEMPTY here, is it
This shows that it would be interesting to manage to install skeleton
coverage analysis to the test suite.
-** Table definitions
-It should be very easy to factor the definition of the various tables,
-including the separation bw declaration and definition. See for
-instance b4_table_define in lalr1.cc. This way, we could even factor
-C vs. C++ definitions.
-
* From lalr1.cc to yacc.c
** Single stack
Merging the three stacks in lalr1.cc simplified the code, prompted for
The code bw glr.c and yacc.c is really alike, we can certainly factor
some parts.
-* Header guards
-
-From Franc,ois: should we keep the directory part in the CPP guard?
-
-
-* Yacc.c: CPP Macros
-
-Do some people use YYPURE, YYLSP_NEEDED like we do in the test suite?
-They should not: it is not documented. But if they need to, let's
-find something clean (not like YYLSP_NEEDED...).
-
-
-* Installation
-
-* Documentation
-Before releasing, make sure the documentation ("Understanding your
-parser") refers to the current `output' format.
* Report
keep $default? See the following point.
** Disabled Reductions
-See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
+See 'tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
what we want to do.
** Documentation
Extend with error productions. The hard part will probably be finding
the right rule so that a single state does not exhibit too many yet
-undocumented ``features''. Maybe an empty action ought to be
+undocumented ''features''. Maybe an empty action ought to be
presented too. Shall we try to make a single grammar with all these
features, or should we have several very small grammars?
* Extensions
-** Labeling the symbols
-Have a look at the Lemon parser generator: instead of $1, $2 etc. they
-can name the values. This is much more pleasant. For instance:
-
- exp (res): exp (a) '+' exp (b) { $res = $a + $b; };
-
-I love this. I have been bitten too often by the removal of the
-symbol, and forgetting to shift all the $n to $n-1. If you are
-unlucky, it compiles...
-
-But instead of using $a etc., we can use regular variables. And
-instead of using (), I propose to use `:' (again). Paul suggests
-supporting `->' in addition to `:' to separate LHS and RHS. In other
-words:
-
- r:exp -> a:exp '+' b:exp { r = a + b; };
-
-That requires an significant improvement of the grammar parser. Using
-GLR would be nice. It also requires that Bison know the type of the
-symbols (which will be useful for %include anyway). So we have some
-time before...
-
-Note that there remains the problem of locations: `@r'?
-
-
** $-1
We should find a means to provide an access to values deep in the
stack. For instance, instead of
- baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; }
+ baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; }
we should be able to have:
* Unit rules
Maybe we could expand unit rules, i.e., transform
- exp: arith | bool;
- arith: exp '+' exp;
- bool: exp '&' exp;
+ exp: arith | bool;
+ arith: exp '+' exp;
+ bool: exp '&' exp;
into
- exp: exp '+' exp | exp '&' exp;
+ exp: exp '+' exp | exp '&' exp;
when there are no actions. This can significantly speed up some
-grammars. I can't find the papers. In particular the book `LR
+grammars. I can't find the papers. In particular the book 'LR
parsing: Theory and Practice' is impossible to find, but according to
-`Parsing Techniques: a Practical Guide', it includes information about
+'Parsing Techniques: a Practical Guide', it includes information about
this issue. Does anybody have it?
Some history of Bison and some bibliography would be most welcome.
Are there any Texinfo standards for bibliography?
-** %printer
-Wow, %printer is not documented. Clearly mark YYPRINT as obsolete.
-
-* Java, Fortran, etc.
-
-
* Coding system independence
Paul notes:
- Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is
- 255). It also assumes that the 8-bit character encoding is
- the same for the invocation of 'bison' as it is for the
- invocation of 'cc', but this is not necessarily true when
- people run bison on an ASCII host and then use cc on an EBCDIC
- host. I don't think these topics are worth our time
- addressing (unless we find a gung-ho volunteer for EBCDIC or
- PDP-10 ports :-) but they should probably be documented
- somewhere.
-
- More importantly, Bison does not currently allow NUL bytes in
- tokens, either via escapes (e.g., "x\0y") or via a NUL byte in
- the source code. This should get fixed.
+ Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is
+ 255). It also assumes that the 8-bit character encoding is
+ the same for the invocation of 'bison' as it is for the
+ invocation of 'cc', but this is not necessarily true when
+ people run bison on an ASCII host and then use cc on an EBCDIC
+ host. I don't think these topics are worth our time
+ addressing (unless we find a gung-ho volunteer for EBCDIC or
+ PDP-10 ports :-) but they should probably be documented
+ somewhere.
-* --graph
-Show reductions.
+ More importantly, Bison does not currently allow NUL bytes in
+ tokens, either via escapes (e.g., "x\0y") or via a NUL byte in
+ the source code. This should get fixed.
* Broken options ?
** %token-table
** Skeleton strategy
Must we keep %token-table?
-* BTYacc
-See if we can integrate backtracking in Bison. Charles-Henri de
-Boysson <de-boy_c@epita.fr> has been working on this, but never gave
-the results.
-
-Vadim Maslow, the maintainer of BTYacc was once contacted. Adjusting
-the Bison grammar parser will be needed to support some extra BTYacc
-features. This is less urgent.
-
-** Keeping the conflicted actions
-First, analyze the differences between byacc and btyacc (I'm referring
-to the executables). Find where the conflicts are preserved.
-
-** Compare with the GLR tables
-See how isomorphic the way BTYacc and the way the GLR adjustments in
-Bison are compatible. *As much as possible* one should try to use the
-same implementation in the Bison executables. I insist: it should be
-very feasible to use the very same conflict tables.
-
-** Adjust the skeletons
-Import the skeletons for C and C++.
-
-
* Precedence
** Partial order
http://lists.gnu.org/archive/html/bison-patches/2009-09/msg00086.html
+
+Local Variables:
+mode: outline
+coding: utf-8
+End:
+
-----
-Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008, 2009, 2010 Free
-Software Foundation, Inc.
+Copyright (C) 2001-2004, 2006, 2008-2013 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
projects / bison.git / blobdiff