X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/680e8701b5ad9718f18f1493e30134b52bceaaca..9515e8a7f83cbb920491ceaef03f8e0fe0ce8108:/TODO?ds=inline diff --git a/TODO b/TODO index c683e39a..0b12b008 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,119 @@ -*- outline -*- +* 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. + +* 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. + + * Unit rules Maybe we could expand unit rules, i.e., transform @@ -14,15 +128,49 @@ into when there are no actions. This can significantly speed up some grammars. -* Huge Grammars -Currently, not only is Bison unable to handle huge grammars because of -internal limitations (see test `big triangle'). Push the limit beyond -253. Be my guest: fix this! +* 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. + * NEWS Sort from 1.31 NEWS. @@ -55,6 +203,8 @@ have: Where the first part defines struct expression, the second uses it to define YYSTYPE, and the last uses YYSTYPE. Only this order is valid. +Note that we have the same problem with GCC. + * --graph Show reductions. [] @@ -146,3 +296,140 @@ 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. + +* 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. + +* 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. + +* Parsing grammars +Rewrite the reader in Bison. + +* Problems with aliases +From: "Baum, Nathan I" +Subject: Token Alias Bug +To: "'bug-bison@gnu.org'" + +I've noticed a bug in bison. Sadly, our eternally wise sysadmins won't let +us use CVS, so I can't find out if it's been fixed already... + +Basically, I made a program (in flex) that went through a .y file looking +for "..."-tokens, and then outputed a %token +line for it. For single-character ""-tokens, I reasoned, I could just use +[%token 'A' "A"]. However, this causes Bison to output a [#define 'A' 65], +which cppp chokes on, not unreasonably. (And even if cppp didn't choke, I +obviously wouldn't want (char)'A' to be replaced with (int)65 throughout my +code. + +Bison normally forgoes outputing a #define for a character token. However, +it always outputs an aliased token -- even if the token is an alias for a +character token. We don't want that. The problem is in /output.c/, as I +recall. When it outputs the token definitions, it checks for a character +token, and then checks for an alias token. If the character token check is +placed after the alias check, then it works correctly. + +Alias tokens seem to be something of a kludge. What about an [%alias "..."] +command... + + %alias T_IF "IF" + +Hmm. I can't help thinking... What about a --generate-lex option that +creates an .l file for the alias tokens used... (Or an option to make a +gperf file, etc...) + +* Presentation of the report file +From: "Baum, Nathan I" +Subject: Token Alias Bug +To: "'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: +- 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). + +* 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. + +----- + +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.