-*- outline -*-
-* NEWS
-Sort from 1.31 NEWS.
-
-* Prologue
-The %union is declared after the user C declarations. It can be
-a problem if YYSTYPE is declared after the user part. []
-
-Actually, the real problem seems that the %union ought to be output
-where it was defined. For instance, in gettext/intl/plural.y, we
-have:
-
- %{
- ...
- #include "gettextP.h"
- ...
- %}
-
- %union {
- unsigned long int num;
- enum operator op;
- struct expression *exp;
+* 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
+
+** 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?
+
+** 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
+Bison might renumber if the user used number 256. Keep fix and doc?
+Throw away?
+
+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_[] =
+ {
+ 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".
+
+ const char*
+ const parser::yytname_[] =
+ {
+ "\"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;
}
- %{
- ...
- static int yylex PARAMS ((YYSTYPE *lval, const char **pexp));
- ...
- %}
+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
+really possible? The test suite does not exercise this case.
+
+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
+other improvements and also made it faster (probably because memory
+management is performed once instead of three times). I suggest that
+we do the same in yacc.c.
+
+** yysyntax_error
+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
+part of $default. Should we make the two reductions explicit, or just
+keep $default? See the following point.
+
+** Disabled Reductions
+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
+presented too. Shall we try to make a single grammar with all these
+features, or should we have several very small grammars?
+
+** --report=conflict-path
+Provide better assistance for understanding the conflicts by providing
+a sample text exhibiting the (LALR) ambiguity. See the paper from
+DeRemer and Penello: they already provide the algorithm.
+
+** Statically check for potential ambiguities in GLR grammars. See
+<http://www.i3s.unice.fr/~schmitz/papers.html#expamb> for an approach.
+
+
+* 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; };
-Where the first part defines struct expression, the second uses it to
-define YYSTYPE, and the last uses YYSTYPE. Only this order is valid.
+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 + $1; }
+
+we should be able to have:
+
+ foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; }
+
+Or something like this.
+
+** %if and the like
+It should be possible to have %if/%else/%endif. The implementation is
+not clear: should it be lexical or syntactic. Vadim Maslow thinks it
+must be in the scanner: we must not parse what is in a switched off
+part of %if. Akim Demaille thinks it should be in the parser, so as
+to avoid falling into another CPP mistake.
+
+** XML Output
+There are couple of available extensions of Bison targeting some XML
+output. Some day we should consider including them. One issue is
+that they seem to be quite orthogonal to the parsing technique, and
+seem to depend mostly on the possibility to have some code triggered
+for each reduction. As a matter of fact, such hooks could also be
+used to generate the yydebug traces. Some generic scheme probably
+exists in there.
+
+XML output for GNU Bison and gcc
+ http://www.cs.may.ie/~jpower/Research/bisonXML/
+
+XML output for GNU Bison
+ http://yaxx.sourceforge.net/
+
+* Unit rules
+Maybe we could expand unit rules, i.e., transform
+
+ exp: arith | bool;
+ arith: exp '+' exp;
+ bool: exp '&' exp;
+
+into
+
+ 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
+parsing: Theory and Practice' is impossible to find, but according to
+`Parsing Techniques: a Practical Guide', it includes information about
+this issue. Does anybody have it?
+
+
+
+* Documentation
+
+** History/Bibliography
+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.
* --graph
-Show reductions. []
+Show reductions.
* Broken options ?
-** %no-lines [ok]
-** %no-parser []
-** %pure-parser []
-** %semantic-parser []
-** %token-table []
-** Options which could use parse_dquoted_param ().
-Maybe transfered in lex.c.
-*** %skeleton [ok]
-*** %output []
-*** %file-prefix []
-*** %name-prefix []
-
-** Skeleton strategy. []
-Must we keep %no-parser?
- %token-table?
-*** New skeletons. []
-
-* src/print_graph.c
-Find the best graph parameters. []
-
-* doc/bison.texinfo
-** Update
-informations about ERROR_VERBOSE. []
-** Add explainations about
-skeleton muscles. []
-%skeleton. []
-
-* testsuite
-** tests/pure-parser.at []
-New tests.
+** %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
+It is unfortunate that there is a total order for precedence. It
+makes it impossible to have modular precedence information. We should
+move to partial orders (sounds like series/parallel orders to me).
+
+** RR conflicts
+See if we can use precedence between rules to solve RR conflicts. See
+what POSIX says.
+
+
+* $undefined
+From Hans:
+- If the Bison generated parser experiences an undefined number in the
+character range, that character is written out in diagnostic messages, an
+addition to the $undefined value.
+
+Suggest: Change the name $undefined to undefined; looks better in outputs.
+
+
+* Default Action
+From Hans:
+- For use with my C++ parser, I transported the "switch (yyn)" statement
+that Bison writes to the bison.simple skeleton file. This way, I can remove
+the current default rule $$ = $1 implementation, which causes a double
+assignment to $$ which may not be OK under C++, replacing it with a
+"default:" part within the switch statement.
+
+Note that the default rule $$ = $1, when typed, is perfectly OK under C,
+but in the C++ implementation I made, this rule is different from
+$<type_name>$ = $<type_name>1. I therefore think that one should implement
+a Bison option where every typed default rule is explicitly written out
+(same typed ruled can of course be grouped together).
+
+* Pre and post actions.
+From: Florian Krohm <florian@edamail.fishkill.ibm.com>
+Subject: YYACT_EPILOGUE
+To: bug-bison@gnu.org
+X-Sent: 1 week, 4 days, 14 hours, 38 minutes, 11 seconds ago
+
+The other day I had the need for explicitly building the parse tree. I
+used %locations for that and defined YYLLOC_DEFAULT to call a function
+that returns the tree node for the production. Easy. But I also needed
+to assign the S-attribute to the tree node. That cannot be done in
+YYLLOC_DEFAULT, because it is invoked before the action is executed.
+The way I solved this was to define a macro YYACT_EPILOGUE that would
+be invoked after the action. For reasons of symmetry I also added
+YYACT_PROLOGUE. Although I had no use for that I can envision how it
+might come in handy for debugging purposes.
+All is needed is to add
+
+#if YYLSP_NEEDED
+ YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen));
+#else
+ YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen);
+#endif
+
+at the proper place to bison.simple. Ditto for YYACT_PROLOGUE.
+
+I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE
+to bison. If you're interested, I'll work on a patch.
+
+* 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
+
+-----
+
+Copyright (C) 2001-2004, 2006, 2008-2010 Free Software Foundation, Inc.
+
+This file is part of Bison, the GNU Compiler Compiler.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
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