X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/308a2f7637aa4f3dd2aa9cb3cf65e5de991b7d6f..87675353bfb6d024d99d0b0298e65c9897600706:/TODO diff --git a/TODO b/TODO index c056bbbb..97505830 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,53 @@ -*- outline -*- +* URGENT: Documenting C++ output +Write a first documentation for C++ output. + +* Report and 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. + +* Report and Disabled Reductions +See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide +what we want to do. + +* 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, ?). Should we also rename `$'? +BYacc uses `$end'. `$eof' is attracting, but after all we may be +parsing a string, a stream etc. + +* 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 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? + +* 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_ @@ -21,130 +69,10 @@ When implementing multiple-%union support, bare the following in mind: char *sval; } -* Experimental report features -Decide whether they should be enabled, or optional. For instance, on: - - input: - exp - | input exp - ; - - exp: - token1 "1" - | token2 "2" - | token3 "3" - ; - - token1: token; - token2: token; - token3: token; - -the traditional Bison reports: - - state 0 - - $axiom -> . input $ (rule 0) - - token shift, and go to state 1 - - input go to state 2 - exp go to state 3 - token1 go to state 4 - token2 go to state 5 - token3 go to state 6 - - state 1 - - token1 -> token . (rule 6) - token2 -> token . (rule 7) - token3 -> token . (rule 8) - - "2" reduce using rule 7 (token2) - "3" reduce using rule 8 (token3) - $default reduce using rule 6 (token1) - -while with --trace, i.e., when enabling both the display of non-core -item sets and the display of lookaheads, Bison now displays: - - state 0 - - $axiom -> . input $ (rule 0) - input -> . exp (rule 1) - input -> . input exp (rule 2) - exp -> . token1 "1" (rule 3) - exp -> . token2 "2" (rule 4) - exp -> . token3 "3" (rule 5) - token1 -> . token (rule 6) - token2 -> . token (rule 7) - token3 -> . token (rule 8) - - token shift, and go to state 1 - - input go to state 2 - exp go to state 3 - token1 go to state 4 - token2 go to state 5 - token3 go to state 6 - - state 1 - - token1 -> token . ["1"] (rule 6) - token2 -> token . ["2"] (rule 7) - token3 -> token . ["3"] (rule 8) - - "2" reduce using rule 7 (token2) - "3" reduce using rule 8 (token3) - $default reduce using rule 6 (token1) - -so decide whether this should be an option, or always enabled. I'm in -favor of making it the default, but maybe we should tune the output to -distinguish core item sets from non core: - - state 0 - Core: - $axiom -> . input $ (rule 0) - - Derived: - input -> . exp (rule 1) - input -> . input exp (rule 2) - exp -> . token1 "1" (rule 3) - exp -> . token2 "2" (rule 4) - exp -> . token3 "3" (rule 5) - token1 -> . token (rule 6) - token2 -> . token (rule 7) - token3 -> . token (rule 8) - - token shift, and go to state 1 - - input go to state 2 - exp go to state 3 - token1 go to state 4 - token2 go to state 5 - token3 go to state 6 - - -> So, it seems clear that it has to be an additional option :) - -Paul: - - There will be further such options in the future, so I'd make - them all operands of the --report option. E.g., you could do - something like this: - - --report=state --report=lookahead --report=itemset - --report=conflict-path - - where "--verbose" is equivalent to "--report=state", and where - "--report=conflict-path" reports each path to a conflict - state. - - (As a minor point, I prefer avoiding plurals in option names. - It's partly for brevity, and partly to avoid wearing out the - 's' keys in our keyboards. :-) - -To implement this, see in the Fileutils the latest versions of -argmatch and so forth. - +* --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: @@ -159,77 +87,6 @@ Paul notes: PDP-10 ports :-) but they should probably be documented somewhere. -* 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 @@ -242,7 +99,10 @@ 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: @@ -268,11 +128,6 @@ 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. @@ -281,12 +136,6 @@ 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. - * --graph Show reductions. [] @@ -321,59 +170,6 @@ skeleton muscles. [] ** tests/pure-parser.at [] New tests. -* Debugging parsers - -From Greg McGary: - -akim demaille 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. @@ -382,9 +178,6 @@ 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. @@ -397,25 +190,6 @@ move to partial orders. This will be possible with a Bison parser for the grammar, as it will make it much easier to extend the grammar. -* Parsing grammars -Rewrite the reader in Flex/Bison. There will be delicate parts, in -particular, expect the scanner to be hard to write. Many interesting -features cannot be implemented without such a new reader. - -* 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 @@ -440,9 +214,6 @@ a Bison option where every typed default rule is explicitly written out Note: Robert Anisko handles this. He knows how to do it. -* Documenting C++ output -Write a first documentation for C++ output. - * 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 @@ -481,23 +252,27 @@ 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. +This file is part of GNU Bison. -GNU Autoconf is free software; you can redistribute it and/or modify +GNU Bison 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, +GNU Bison 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 +along with Bison; see the file COPYING. 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