X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/88bce5a2ef15e5b508749e75ddad709aca85b019..67411a88a0668401f9583526668e3930762c55f0:/TODO?ds=sidebyside diff --git a/TODO b/TODO index 56038fc6..09fce089 100644 --- a/TODO +++ b/TODO @@ -1,73 +1,188 @@ --*- outline -*- +* Short term +** Graphviz display code thoughts +The code for the --graph option is over two files: print_graph, and +graphviz. This is because Bison used to also produce VCG graphs, but since +this is no longer true, maybe we could consider these files for fusion. + +An other consideration worth noting is that print_graph.c (correct me if I +am wrong) should contain generic functions, whereas graphviz.c and other +potential files should contain just the specific code for that output +format. It will probably prove difficult to tell if the implementation is +actually generic whilst only having support for a single format, but it +would be nice to keep stuff a bit tidier: right now, the construction of the +bitset used to show reductions is in the graphviz-specific code, and on the +opposite side we have some use of \l, which is graphviz-specific, in what +should be generic code. + +Little effort seems to have been given to factoring these files and their +rint{,-xml} counterpart. We would very much like to re-use the pretty format +of states from .output for the graphs, etc. + +Also, the underscore in print_graph.[ch] isn't very fitting considering the +dashes in the other filenames. -* URGENT: Documenting C++ output -Write a first documentation for C++ output. +Since graphviz dies on medium-to-big grammars, maybe consider an other tool? +** push-parser +Check it too when checking the different kinds of parsers. And be +sure to check that the initial-action is performed once per parsing. -* Documentation -Before releasing, make sure the documentation refers to the current -`output' format. +** m4 names +b4_shared_declarations is no longer what it is. Make it +b4_parser_declaration for instance. + +** yychar in lalr1.cc +There is a large difference bw maint and master on the handling of +yychar (which was removed in lalr1.cc). See what needs to be +back-ported. + + + /* User semantic actions sometimes alter yychar, and that requires + that yytoken be updated with the new translation. We take the + approach of translating immediately before every use of yytoken. + One alternative is translating here after every semantic action, + but that translation would be missed if the semantic action + invokes YYABORT, YYACCEPT, or YYERROR immediately after altering + yychar. In the case of YYABORT or YYACCEPT, an incorrect + destructor might then be invoked immediately. In the case of + YYERROR, subsequent parser actions might lead to an incorrect + destructor call or verbose syntax error message before the + lookahead is translated. */ + + /* Make sure we have latest lookahead translation. See comments at + user semantic actions for why this is necessary. */ + yytoken = yytranslate_ (yychar); + + +** stack.hh +Get rid of it. The original idea is nice, but actually it makes +the code harder to follow, and uselessly different from the other +skeletons. + +** Get rid of fake #lines [Bison: ...] +Possibly as simple as checking whether the column number is nonnegative. + +I have seen messages like the following from GCC. + +:0: fatal error: opening dependency file .deps/libltdl/argz.Tpo: No such file or directory + + +** Discuss about %printer/%destroy in the case of C++. +It would be very nice to provide the symbol classes with an operator<< +and a destructor. Unfortunately the syntax we have chosen for +%destroy and %printer make them hard to reuse. For instance, the user +is invited to write something like + + %printer { debug_stream() << $$; } ; +which is hard to reuse elsewhere since it wants to use +"debug_stream()" to find the stream to use. The same applies to +%destroy: we told the user she could use the members of the Parser +class in the printers/destructors, which is not good for an operator<< +since it is no longer bound to a particular parser, it's just a +(standalone symbol). -* Error messages -Some are really funky. For instance +** Rename LR0.cc +as lr0.cc, why upper case? - type clash (`%s' `%s') on default action +* 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? -is really weird. Revisit them all. +Also, why don't we output the token name of the error token in the +output? It is explicitly skipped: -* Stupid error messages -An example shows it easily: + /* Skip error token and tokens without identifier. */ + if (sym != errtoken && id) -src/bison/tests % ./testsuite -k calc,location,error-verbose -l -GNU Bison 1.49a test suite test groups: +Of course there are issues with name spaces, but if we disable we have +something which seems to be more simpler and more consistent instead +of the special case YYERRCODE. - NUM: FILENAME:LINE TEST-GROUP-NAME - KEYWORDS + enum yytokentype { + error = 256, + // ... + }; - 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 '(' +We could (should?) also treat the case of the undef_token, which is +numbered 257 for yylex, and 2 internal. Both appear for instance in +toknum: -* 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. + const unsigned short int + parser::yytoken_number_[] = + { + 0, 256, 257, 258, 259, 260, 261, 262, 263, 264, +while here -* 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? + enum yytokentype { + TOK_EOF = 0, + TOK_EQ = 258, + +so both 256 and 257 are "mysterious". + + const char* + const parser::yytname_[] = + { + "\"end of command\"", "error", "$undefined", "\"=\"", "\"break\"", + + +** yychar == yyempty_ +The code in yyerrlab reads: + + if (yychar <= YYEOF) + { + /* Return failure if at end of input. */ + if (yychar == YYEOF) + YYABORT; + } + +There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF. +But I can't produce the situation where yychar is YYEMPTY here, is it +really possible? The test suite does not exercise this case. + +This shows that it would be interesting to manage to install skeleton +coverage analysis to the test suite. + +* From lalr1.cc to yacc.c +** Single stack +Merging the three stacks in lalr1.cc simplified the code, prompted for +other improvements and also made it faster (probably because memory +management is performed once instead of three times). I suggest that +we do the same in yacc.c. + +** yysyntax_error +The code bw glr.c and yacc.c is really alike, we can certainly factor +some parts. * Report +** Figures +Some statistics about the grammar and the parser would be useful, +especially when asking the user to send some information about the +grammars she is working on. We should probably also include some +information about the variables (I'm not sure for instance we even +specify what LR variant was used). + ** 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 +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 +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 +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? @@ -76,50 +191,61 @@ 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 + for an approach. + -* Extentions +* Extensions -** 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... +** $-1 +We should find a means to provide an access to values deep in the +stack. For instance, instead of -** 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. + baz: qux { $$ = $-1 + $0 + $1; } -When implementing multiple-%union support, bare the following in mind: +we should be able to have: -- when --yacc, this must be flagged as an error. Don't make it fatal - though. + foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } -- The #line must now appear *inside* the definition of yystype. - Something like +Or something like this. - { - #line 12 "foo.y" - int ival; - #line 23 "foo.y" - char *sval; - } +** %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. + +** 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; + exp: arith | bool; + arith: exp '+' exp; + bool: exp '&' exp; into - exp: exp '+' exp | exp '&' exp; + 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 +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 +'Parsing Techniques: a Practical Guide', it includes information about this issue. Does anybody have it? @@ -130,82 +256,27 @@ this issue. Does anybody have it? 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. + 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. - - -* --graph -Show reductions. [] + 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. * 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. - -* 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. - -** 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. - +** %token-table +** Skeleton strategy +Must we keep %token-table? * Precedence @@ -214,18 +285,6 @@ 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). -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. @@ -254,20 +313,6 @@ $$ = $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 @@ -296,27 +341,47 @@ 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. +* Better graphics +Equip the parser with a means to create the (visual) parse tree. + +* Complaint submessage indentation. +We already have an implementation that works fairly well for named +reference messages, but it would be nice to use it consistently for all +submessages from Bison. For example, the "previous definition" +submessage or the list of correct values for a %define variable might +look better with indentation. + +However, the current implementation makes the assumption that the +location printed on the first line is not usually much shorter than the +locations printed on the submessage lines that follow. That assumption +may not hold true as often for some kinds of submessages especially if +we ever support multiple grammar files. + +Here's a proposal for how a new implementation might look: + + http://lists.gnu.org/archive/html/bison-patches/2009-09/msg00086.html + + +Local Variables: +mode: outline +coding: utf-8 +End: ----- -Copyright (C) 2001, 2002 Free Software Foundation, Inc. +Copyright (C) 2001-2004, 2006, 2008-2013 Free Software Foundation, Inc. -This file is part of GNU Bison. +This file is part of Bison, the GNU Compiler Compiler. -GNU Bison is free software; you can redistribute it and/or modify +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 2, or (at your option) -any later version. +the Free Software Foundation, either version 3 of the License, or +(at your option) any later version. -GNU Bison is distributed in the hope that it will be useful, +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 Bison; see the file COPYING. If not, write to -the Free Software Foundation, Inc., 59 Temple Place - Suite 330, -Boston, MA 02111-1307, USA. +along with this program. If not, see .