--*- outline -*-
+* Short term
+** 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.
+
+I have seen messages like the following from GCC.
+
+<built-in>:0: fatal error: opening dependency file .deps/libltdl/argz.Tpo: No such file or directory
+
+
+** Discuss about %printer/%destroy in the case of C++.
+It would be very nice to provide the symbol classes with an operator<<
+and a destructor. Unfortunately the syntax we have chosen for
+%destroy and %printer make them hard to reuse. For instance, the user
+is invited to write something like
+
+ %printer { debug_stream() << $$; } <my_type>;
+
+which is hard to reuse elsewhere since it wants to use
+"debug_stream()" to find the stream to use. The same applies to
+%destroy: we told the user she could use the members of the Parser
+class in the printers/destructors, which is not good for an operator<<
+since it is no longer bound to a particular parser, it's just a
+(standalone symbol).
+
+** Rename LR0.cc
+as lr0.cc, why upper case?
* Various
** YYERRCODE
Bison might renumber if the user used number 256. Keep fix and doc?
Throw away?
-** 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)
+Also, why don't we output the token name of the error token in the
+output? It is explicitly skipped:
+
+ /* Skip error token and tokens without identifier. */
+ if (sym != errtoken && id)
+
+Of course there are issues with name spaces, but if we disable we have
+something which seems to be more simpler and more consistent instead
+of the special case YYERRCODE.
+
+ enum yytokentype {
+ error = 256,
+ // ...
+ };
+
+
+We could (should?) also treat the case of the undef_token, which is
+numbered 257 for yylex, and 2 internal. Both appear for instance in
+toknum:
+
+ const unsigned short int
+ parser::yytoken_number_[] =
{
- fprintf (stderr, "%s\n", msg);
- }
+ 0, 256, 257, 258, 259, 260, 261, 262, 263, 264,
+
+while here
+
+ enum yytokentype {
+ TOK_EOF = 0,
+ TOK_EQ = 258,
+
+so both 256 and 257 are "mysterious".
- int
- main (void)
+ const char*
+ const parser::yytname_[] =
{
- yydebug = !!getenv("YYDEBUG");
- return yyparse ();
- }
+ "\"end of command\"", "error", "$undefined", "\"=\"", "\"break\"",
+
** 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
we do the same in yacc.c.
** yysyntax_error
-In lalr1.cc we invoke it with the translated lookahead (yytoken), and
-yacc.c uses yychar. I don't see why.
-
-** yysyntax_error
-The use of switch to select yyfmt in lalr1.cc seems simpler than
-what's done in yacc.c.
+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
+** Figures
+Some statistics about the grammar and the parser would be useful,
+especially when asking the user to send some information about the
+grammars she is working on. We should probably also include some
+information about the variables (I'm not sure for instance we even
+specify what LR variant was used).
+
** GLR
How would Paul like to display the conflicted actions? In particular,
what when two reductions are possible on a given lookahead token, but one is
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?
-
-
-* 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
* Better graphics
Equip the parser with a means to create the (visual) parse tree.
+* Complaint submessage indentation.
+We already have an implementation that works fairly well for named
+reference messages, but it would be nice to use it consistently for all
+submessages from Bison. For example, the "previous definition"
+submessage or the list of correct values for a %define variable might
+look better with indentation.
+
+However, the current implementation makes the assumption that the
+location printed on the first line is not usually much shorter than the
+locations printed on the submessage lines that follow. That assumption
+may not hold true as often for some kinds of submessages especially if
+we ever support multiple grammar files.
+
+Here's a proposal for how a new implementation might look:
+
+ 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 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