-*- outline -*-
-* Several %unions
-I think this is a pleasant (but useless currently) feature, but in the
-future, I want a means to %include other bits of grammars, and _then_
-it will be important for the various bits to define their needs in
-%union.
+* Various
+** 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?
+
+** 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++];
+ }
-When implementing multiple-%union support, bare the following in mind:
+ static void
+ yyerror (const char *msg)
+ {
+ fprintf (stderr, "%s\n", msg);
+ }
-- when --yacc, this must be flagged as an error. Don't make it fatal
- though.
+ int
+ main (void)
+ {
+ yydebug = !!getenv("YYDEBUG");
+ return yyparse ();
+ }
-- The #line must now appear *inside* the definition of yystype.
- Something like
- {
- #line 12 "foo.y"
- int ival;
- #line 23 "foo.y"
- char *sval;
- }
-
-* Experimental report features
-Decide whether they should be enabled, or optional. For instance, on:
+* Header guards
- input:
- exp
- | input exp
- ;
+From Franc,ois: should we keep the directory part in the CPP guard?
- exp:
- token1 "1"
- | token2 "2"
- | token3 "3"
- ;
- token1: token;
- token2: token;
- token3: token;
+* Yacc.c: CPP Macros
-the traditional Bison reports:
+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...).
- state 0
- $axiom -> . input $ (rule 0)
+* Installation
- token shift, and go to state 1
+* Documentation
+Before releasing, make sure the documentation ("Understanding your
+parser") refers to the current `output' format.
- input go to state 2
- exp go to state 3
- token1 go to state 4
- token2 go to state 5
- token3 go to state 6
+* lalr1.cc
+** I18n
+Catch up with yacc.c.
- state 1
+* Report
- token1 -> token . (rule 6)
- token2 -> token . (rule 7)
- token3 -> token . (rule 8)
+** 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.
- "2" reduce using rule 7 (token2)
- "3" reduce using rule 8 (token3)
- $default reduce using rule 6 (token1)
+** Disabled Reductions
+See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
+what we want to do.
-while with --trace, i.e., when enabling both the display of non-core
-item sets and the display of lookaheads, Bison now displays:
+** 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?
- state 0
+** --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.
- $axiom -> . input $ (rule 0)
- input -> . exp (rule 1)
- input -> . input exp (rule 2)
- exp -> . token1 "1" (rule 3)
- exp -> . token2 "2" (rule 4)
- exp -> . token3 "3" (rule 5)
- token1 -> . token (rule 6)
- token2 -> . token (rule 7)
- token3 -> . token (rule 8)
+** Statically check for potential ambiguities in GLR grammars. See
+<http://www.i3s.unice.fr/~schmitz/papers.html#expamb> for an approach.
- token shift, and go to state 1
- input go to state 2
- exp go to state 3
- token1 go to state 4
- token2 go to state 5
- token3 go to state 6
+* Extensions
- state 1
+** 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:
- token1 -> token . ["1"] (rule 6)
- token2 -> token . ["2"] (rule 7)
- token3 -> token . ["3"] (rule 8)
+ exp (res): exp (a) '+' exp (b) { $res = $a + $b; };
- "2" reduce using rule 7 (token2)
- "3" reduce using rule 8 (token3)
- $default reduce using rule 6 (token1)
+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...
-so decide whether this should be an option, or always enabled. I'm in
-favor of making it the default, but maybe we should tune the output to
-distinguish core item sets from non core:
+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:
- state 0
- Core:
- $axiom -> . input $ (rule 0)
+ r:exp -> a:exp '+' b:exp { r = a + b; };
- Derived:
- input -> . exp (rule 1)
- input -> . input exp (rule 2)
- exp -> . token1 "1" (rule 3)
- exp -> . token2 "2" (rule 4)
- exp -> . token3 "3" (rule 5)
- token1 -> . token (rule 6)
- token2 -> . token (rule 7)
- token3 -> . token (rule 8)
+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...
- token shift, and go to state 1
+Note that there remains the problem of locations: `@r'?
- input go to state 2
- exp go to state 3
- token1 go to state 4
- token2 go to state 5
- token3 go to state 6
+** $-1
+We should find a means to provide an access to values deep in the
+stack. For instance, instead of
-> So, it seems clear that it has to be an additional option :)
+ baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; }
-Paul:
+we should be able to have:
- There will be further such options in the future, so I'd make
- them all operands of the --report option. E.g., you could do
- something like this:
+ foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; }
- --report=state --report=lookahead --report=itemset
- --report=conflict-path
+Or something like this.
- where "--verbose" is equivalent to "--report=state", and where
- "--report=conflict-path" reports each path to a conflict
- state.
+** %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.
- (As a minor point, I prefer avoiding plurals in option names.
- It's partly for brevity, and partly to avoid wearing out the
- 's' keys in our keyboards. :-)
+** 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.
-To implement this, see in the Fileutils the latest versions of
-argmatch and so forth.
+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?
+
+
+
+* Java, Fortran, etc.
* Coding system independence
PDP-10 ports :-) but they should probably be documented
somewhere.
-* Output directory
-Akim:
-
-| I consider this to be a bug in bison:
-|
-| /tmp % mkdir src
-| /tmp % cp ~/src/bison/tests/calc.y src
-| /tmp % mkdir build && cd build
-| /tmp/build % bison ../src/calc.y
-| /tmp/build % cd ..
-| /tmp % ls -l build src
-| build:
-| total 0
-|
-| src:
-| total 32
-| -rw-r--r-- 1 akim lrde 27553 oct 2 16:31 calc.tab.c
-| -rw-r--r-- 1 akim lrde 3335 oct 2 16:31 calc.y
-|
-|
-| Would it be safe to change this behavior to something more reasonable?
-| Do you think some people depend upon this?
-
-Jim:
-
-Is it that behavior documented?
-If so, then it's probably not reasonable to change it.
-I've Cc'd the automake list, because some of automake's
-rules use bison through $(YACC) -- though I'll bet they
-all use it in yacc-compatible mode.
-
-Pavel:
-
-Hello, Jim and others!
-
-> Is it that behavior documented?
-> If so, then it's probably not reasonable to change it.
-> I've Cc'd the automake list, because some of automake's
-> rules use bison through $(YACC) -- though I'll bet they
-> all use it in yacc-compatible mode.
-
-Yes, Automake currently used bison in Automake-compatible mode, but it
-would be fair for Automake to switch to the native mode as long as the
-processed files are distributed and "missing" emulates bison.
-
-In any case, the makefiles should specify the output file explicitly
-instead of relying on weird defaults.
-
-> | src:
-> | total 32
-> | -rw-r--r-- 1 akim lrde 27553 oct 2 16:31 calc.tab.c
-> | -rw-r--r-- 1 akim lrde 3335 oct 2 16:31 calc.y
-
-This is not _that_ ugly as it seems - with Automake you want to put
-sources where they belong - to the source directory.
-
-> | This is not _that_ ugly as it seems - with Automake you want to put
-> | sources where they belong - to the source directory.
->
-> The difference source/build you are referring to is based on Automake
-> concepts. They have no sense at all for tools such as bison or gcc
-> etc. They have input and output. I do not want them to try to grasp
-> source/build. I want them to behave uniformly: output *here*.
-
-I realize that.
-
-It's unfortunate that the native mode of Bison behaves in a less uniform
-way than the yacc mode. I agree with your point. Bison maintainters may
-want to fix it along with the documentation.
+ 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.
-* Unit rules
-Maybe we could expand unit rules, i.e., transform
+* Broken options ?
+** %token-table
+** Skeleton strategy
+Must we keep %token-table?
- exp: arith | bool;
- arith: exp '+' exp;
- bool: exp '&' exp;
+* 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.
-into
+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.
- exp: exp '+' exp | exp '&' exp;
+** Keeping the conflicted actions
+First, analyze the differences between byacc and btyacc (I'm referring
+to the executables). Find where the conflicts are preserved.
-when there are no actions. This can significantly speed up some
-grammars.
-
-* Stupid error messages
-An example shows it easily:
-
-src/bison/tests % ./testsuite -k calc,location,error-verbose -l
-GNU Bison 1.49a test suite test groups:
-
- NUM: FILENAME:LINE TEST-GROUP-NAME
- KEYWORDS
-
- 51: calc.at:440 Calculator --locations --yyerror-verbose
- 52: calc.at:442 Calculator --defines --locations --name-prefix=calc --verbose --yacc --yyerror-verbose
- 54: calc.at:445 Calculator --debug --defines --locations --name-prefix=calc --verbose --yacc --yyerror-verbose
-src/bison/tests % ./testsuite 51 -d
-## --------------------------- ##
-## GNU Bison 1.49a test suite. ##
-## --------------------------- ##
- 51: calc.at:440 ok
-## ---------------------------- ##
-## All 1 tests were successful. ##
-## ---------------------------- ##
-src/bison/tests % cd ./testsuite.dir/51
-tests/testsuite.dir/51 % echo "()" | ./calc
-1.2-1.3: parse error, unexpected ')', expecting error or "number" or '-' or '('
-
-* yyerror, yyprint interface
-It should be improved, in particular when using Bison features such as
-locations, and YYPARSE_PARAMS. For the time being, it is recommended
-to #define yyerror and yyprint to steal internal variables...
-
-* read_pipe.c
-This is not portable to DOS for instance. Implement a more portable
-scheme. Sources of inspiration include GNU diff, and Free Recode.
-
-* Memory leaks in the generator
-A round of memory leak clean ups would be most welcome. Dmalloc,
-Checker GCC, Electric Fence, or Valgrind: you chose your tool.
-
-* Memory leaks in the parser
-The same applies to the generated parsers. In particular, this is
-critical for user data: when aborting a parsing, when handling the
-error token etc., we often throw away yylval without giving a chance
-of cleaning it up to the user.
+** 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.
-* --graph
-Show reductions. []
+** Adjust the skeletons
+Import the skeletons for C and C++.
-* Broken options ?
-** %no-lines [ok]
-** %no-parser []
-** %pure-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.
-
-* Debugging parsers
-
-From Greg McGary:
-
-akim demaille <akim.demaille@epita.fr> writes:
-
-> With great pleasure! Nonetheless, things which are debatable
-> (or not, but just `big') should be discuss in `public': something
-> like help- or bug-bison@gnu.org is just fine. Jesse and I are there,
-> but there is also Jim and some other people.
-
-I have no idea whether it qualifies as big or controversial, so I'll
-just summarize for you. I proposed this change years ago and was
-surprised that it was met with utter indifference!
-
-This debug feature is for the programs/grammars one develops with
-bison, not for debugging bison itself. I find that the YYDEBUG
-output comes in a very inconvenient format for my purposes.
-When debugging gcc, for instance, what I want is to see a trace of
-the sequence of reductions and the line#s for the semantic actions
-so I can follow what's happening. Single-step in gdb doesn't cut it
-because to move from one semantic action to the next takes you through
-lots of internal machinery of the parser, which is uninteresting.
-
-The change I made was to the format of the debug output, so that it
-comes out in the format of C error messages, digestible by emacs
-compile mode, like so:
-
-grammar.y:1234: foo: bar(0x123456) baz(0x345678)
-
-where "foo: bar baz" is the reduction rule, whose semantic action
-appears on line 1234 of the bison grammar file grammar.y. The hex
-numbers on the rhs tokens are the parse-stack values associated with
-those tokens. Of course, yytype might be something totally
-incompatible with that representation, but for the most part, yytype
-values are single words (scalars or pointers). In the case of gcc,
-they're most often pointers to tree nodes. Come to think of it, the
-right thing to do is to make the printing of stack values be
-user-definable. It would also be useful to include the filename &
-line# of the file being parsed, but the main filename & line# should
-continue to be that of grammar.y
-
-Anyway, this feature has saved my life on numerous occasions. The way
-I customarily use it is to first run bison with the traces on, isolate
-the sequence of reductions that interests me, put those traces in a
-buffer and force it into compile-mode, then visit each of those lines
-in the grammar and set breakpoints with C-x SPACE. Then, I can run
-again under the control of gdb and stop at each semantic action.
-With the hex addresses of tree nodes, I can inspect the values
-associated with any rhs token.
-
-You like?
-
-* input synclines
-Some users create their foo.y files, and equip them with #line. Bison
-should recognize these, and preserve them.
-* BTYacc
-See if we can integrate backtracking in Bison. Contact the BTYacc
-maintainers.
+* Precedence
-* Automaton report
-Display more clearly the lookaheads for each item.
+** 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
+** RR conflicts
See if we can use precedence between rules to solve RR conflicts. See
what POSIX says.
-* Precedence
-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.
-
-This will be possible with a Bison parser for the grammar, as it will
-make it much easier to extend the grammar.
-
-* Parsing grammars
-Rewrite the reader in Flex/Bison. There will be delicate parts, in
-particular, expect the scanner to be hard to write. Many interesting
-features cannot be implemented without such a new reader.
-
-* Presentation of the report file
-From: "Baum, Nathan I" <s0009525@chelt.ac.uk>
-Subject: Token Alias Bug
-To: "'bug-bison@gnu.org'" <bug-bison@gnu.org>
-
-I've also noticed something, that whilst not *wrong*, is inconvienient: I
-use the verbose mode to help find the causes of unresolved shift/reduce
-conflicts. However, this mode insists on starting the .output file with a
-list of *resolved* conflicts, something I find quite useless. Might it be
-possible to define a -v mode, and a -vv mode -- Where the -vv mode shows
-everything, but the -v mode only tells you what you need for examining
-conflicts? (Or, perhaps, a "*** This state has N conflicts ***" marker above
-each state with conflicts.)
* $undefined
From Hans:
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
a Bison option where every typed default rule is explicitly written out
(same typed ruled can of course be grouped together).
-Note: Robert Anisko handles this. He knows how to do it.
-
-* Documenting C++ output
-Write a first documentation for C++ output.
-
-* Warnings
-It would be nice to have warning support. See how Autoconf handles
-them, it is fairly well described there. It would be very nice to
-implement this in such a way that other programs could use
-lib/warnings.[ch].
-
-Don't work on this without first announcing you do, as I already have
-thought about it, and know many of the components that can be used to
-implement it.
-
* Pre and post actions.
From: Florian Krohm <florian@edamail.fishkill.ibm.com>
Subject: YYACT_EPILOGUE
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.
+
-----
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+Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008 Free Software Foundation,
+Inc.
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-GNU Autoconf is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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