X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/aef1ffd56f6a9cd1ffcaa9f4c5f496f4f74ea82a..e776192e4fcb3b34d8a279d7cc1ea153e96ae2e7:/TODO diff --git a/TODO b/TODO index 0e385ebc..af8f10fa 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,80 @@ -*- outline -*- +* URGENT: Documenting C++ output +Write a first documentation for C++ output. + +* 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 $n on her +union, doesn't she? + +* 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... + +* documentation +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, ?). + +* Error messages +Some are really funky. For instance + + type clash (`%s' `%s') on default action + +is really weird. Revisit them all. + +* Report documentation +Extend with error. The hard part will probably be finding the right +rule so that a single state does not exhibit to 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? + +* Documentation +Some history of Bison and some bibliography would be most welcome. +Are there any Texinfo standards for bibliography? + +* 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; + } + +* --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. + +* 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. + * Unit rules Maybe we could expand unit rules, i.e., transform @@ -12,7 +87,10 @@ into exp: exp '+' exp | exp '&' exp; when there are no actions. This can significantly speed up some -grammars. +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? * Stupid error messages An example shows it easily: @@ -46,44 +124,6 @@ scheme. Sources of inspiration include GNU diff, and Free Recode. 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; - } - - %{ - ... - static int yylex PARAMS ((YYSTYPE *lval, const char **pexp)); - ... - %} - -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. [] @@ -91,7 +131,6 @@ 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. @@ -180,9 +219,6 @@ 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. - * RR conflicts See if we can use precedence between rules to solve RR conflicts. See what POSIX says. @@ -192,5 +228,92 @@ 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. -* Parsing grammars -Rewrite the reader in Bison. +This will be possible with a Bison parser for the grammar, as it will +make it much easier to extend the grammar. + +* $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 $$ = $1, when typed, is perfectly OK under C, +but in the C++ implementation I made, this rule is different from +$$ = $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 +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. + +* 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. + +GNU Autoconf 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 2, or (at your option) +any later version. + +GNU Autoconf 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 autoconf; see the file COPYING. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA.