Index: bison/src/bison/2.4.1/bison-2.4.1-src/TODO |
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+-*- outline -*- |
+ |
+* 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. |
+ |
+* lalr1.cc |
+** vector |
+Move to using vector, drop stack.hh. |
+ |
+** I18n |
+Catch up with yacc.c. |
+ |
+* Report |
+ |
+** 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; }; |
+ |
+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. |
+ |
+** -D, --define-muscle NAME=VALUE |
+To define muscles via cli. Or maybe support directly NAME=VALUE? |
+ |
+** 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? |
+ |
+ |
+ |
+* 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. |
+ |
+* Broken options ? |
+** %token-table |
+** Skeleton strategy |
+Must we keep %token-table? |
+ |
+* src/print_graph.c |
+Find the best graph parameters. |
+ |
+* BTYacc |
+See if we can integrate backtracking in Bison. Charles-Henri de |
+Boysson <de-boy_c@epita.fr> is working on this, and already has some |
+results. Vadim Maslow, the maintainer of BTYacc was contacted, and we |
+stay in touch with him. 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++. |
+ |
+** Improve the skeletons |
+Have them support yysymprint, yydestruct and so forth. |
+ |
+ |
+* 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). |
+ |
+** 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. |
+ |
+* Better graphics |
+Equip the parser with a means to create the (visual) parse tree. |
+ |
+----- |
+ |
+Copyright (C) 2001, 2002, 2003, 2004, 2006 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/>. |