-*- outline -*-
-* Coding system independence
-Paul notes:
+* URGENT: Documenting C++ output
+Write a first documentation for C++ output.
- 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.
-* Using enums instead of int for tokens.
-Paul suggests:
-
- #ifndef YYTOKENTYPE
- # if defined (__STDC__) || defined (__cplusplus)
- /* Put the tokens into the symbol table, so that GDB and other debuggers
- know about them. */
- enum yytokentype {
- FOO = 256,
- BAR,
- ...
- };
- /* POSIX requires `int' for tokens in interfaces. */
- # define YYTOKENTYPE int
- # endif
- #endif
- #define FOO 256
- #define BAR 257
- ...
-
-> I'm in favor of
->
-> %token FOO 256
-> %token BAR 257
->
-> and Bison moves error into 258.
-
-Yes, I think that's a valid extension too, if the user doesn't define
-the token number for error.
-
-* 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.
+* Error messages
+Some are really funky. For instance
+ type clash (`%s' `%s') on default action
-* 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.
+is really weird. Revisit them all.
* Stupid error messages
An example shows it easily:
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.
-
-* 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;
+
+* value_components_used
+Was defined but not used: where was it coming from? It can't be to
+check if %union is used, since the user is free to $<foo>n on her
+union, doesn't she?
+
+
+* Report
+
+** GLR
+How would Paul like to display the conflicted actions? In particular,
+what when two reductions are possible on a given lookahead, 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.
+
+
+* Extentions
+
+** yyerror, yysymprint 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...
+
+** 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.
+
+When implementing multiple-%union support, bare the following in mind:
+
+- when --yacc, this must be flagged as an error. Don't make it fatal
+ though.
+
+- The #line must now appear *inside* the definition of yystype.
+ Something like
+
+ {
+ #line 12 "foo.y"
+ int ival;
+ #line 23 "foo.y"
+ char *sval;
}
- %{
- ...
- static int yylex PARAMS ((YYSTYPE *lval, const char **pexp));
- ...
- %}
+* 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
+
+** Vocabulary
+Explain $axiom (and maybe change its name: BTYacc names it `goal',
+byacc `$accept' probably based on AT&T Yacc, Meta `Start'...).
+Complete the glossary (item, axiom, ?). Should we also rename `$'?
+BYacc uses `$end'. `$eof' is attracting, but after all we may be
+parsing a string, a stream etc.
+
+** History/Bibliography
+Some history of Bison and some bibliography would be most welcome.
+Are there any Texinfo standards for bibliography?
+
+
+
+
+* 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.
+
-Where the first part defines struct expression, the second uses it to
-define YYSTYPE, and the last uses YYSTYPE. Only this order is valid.
* --graph
Show reductions. []
** %no-lines [ok]
** %no-parser []
** %pure-parser []
-** %semantic-parser []
** %token-table []
** Options which could use parse_dquoted_param ().
Maybe transfered in lex.c.
** 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.
See if we can integrate backtracking in Bison. Contact the BTYacc
maintainers.
-* Automaton report
-Display more clearly the lookaheads for each item.
+** 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 adjustements 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++.
+
+** Improve the skeletons
+Have them support yysymprint, yydestruct and so forth.
-* RR conflicts
-See if we can use precedence between rules to solve RR conflicts. See
-what POSIX says.
* 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.
+move to partial orders (sounds like series/parallel orders to me).
+
+This will be possible with a Bison parser for the grammar, as it will
+make it much easier to extend the grammar.
+
+** Correlation b/w precedence and associativity
+Also, I fail to understand why we have to assign the same
+associativity to operators with the same precedence. For instance,
+why can't I decide that the precedence of * and / is the same, but the
+latter is nonassoc?
+
+If there is really no profound motivation, we should find a new syntax
+to allow specifying this.
+
+** 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).
+
+Note: Robert Anisko handles this. He knows how to do it.
+
+
+* 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
+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.
-* Parsing grammars
-Rewrite the reader in Bison.
+* Move to Graphviz
+Well, VCG seems really dead. Move to Graphviz instead. Also, equip
+the parser with a means to create the (visual) parse tree.
-----
Copyright (C) 2001, 2002 Free Software Foundation, Inc.
-This file is part of GNU Autoconf.
+This file is part of GNU Bison.
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it under the terms of the GNU General Public License as published by
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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