X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/308a2f7637aa4f3dd2aa9cb3cf65e5de991b7d6f..015e86a7b2224848f3f1f29d7bdbf8e31d8bee34:/TODO diff --git a/TODO b/TODO index c056bbbb..b2bca354 100644 --- a/TODO +++ b/TODO @@ -1,149 +1,150 @@ -*- outline -*- -* 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. +* Header guards -When implementing multiple-%union support, bare the following in mind: +From Franc,ois: should we keep the directory part in the CPP guard? -- 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 +* Yacc.c: CPP Macros - { - #line 12 "foo.y" - int ival; - #line 23 "foo.y" - char *sval; - } - -* Experimental report features -Decide whether they should be enabled, or optional. For instance, on: +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...). - input: - exp - | input exp - ; - exp: - token1 "1" - | token2 "2" - | token3 "3" - ; +* Installation - token1: token; - token2: token; - token3: token; +* Documentation +Before releasing, make sure the documentation ("Understanding your +parser") refers to the current `output' format. -the traditional Bison reports: +* lalr1.cc +** vector +Move to using vector, drop stack.hh. - state 0 +** I18n +Catch up with yacc.c. - $axiom -> . input $ (rule 0) +* Report - token shift, and go to state 1 +** 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. - 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 +** Disabled Reductions +See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide +what we want to do. - state 1 +** 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? - token1 -> token . (rule 6) - token2 -> token . (rule 7) - token3 -> token . (rule 8) +** --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. - "2" reduce using rule 7 (token2) - "3" reduce using rule 8 (token3) - $default reduce using rule 6 (token1) +** Statically check for potential ambiguities in GLR grammars. See + for an approach. -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 +* Extensions - $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) +** 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: - token shift, and go to state 1 + exp (res): exp (a) '+' exp (b) { $res = $a + $b; }; - 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 +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... - state 1 +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: - token1 -> token . ["1"] (rule 6) - token2 -> token . ["2"] (rule 7) - token3 -> token . ["3"] (rule 8) + r:exp -> a:exp '+' b:exp { r = a + b; }; - "2" reduce using rule 7 (token2) - "3" reduce using rule 8 (token3) - $default reduce using rule 6 (token1) +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... -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: +Note that there remains the problem of locations: `@r'? - 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) +** $-1 +We should find a means to provide an access to values deep in the +stack. For instance, instead of - token shift, and go to state 1 + baz: qux { $$ = $-1 + $0 + $1; } - input go to state 2 - exp go to state 3 - token1 go to state 4 - token2 go to state 5 - token3 go to state 6 +we should be able to have: + foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } -> So, it seems clear that it has to be an additional option :) +Or something like this. -Paul: +** %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. - 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: +** -D, --define-muscle NAME=VALUE +To define muscles via cli. Or maybe support directly NAME=VALUE? - --report=state --report=lookahead --report=itemset - --report=conflict-path +** 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. - where "--verbose" is equivalent to "--report=state", and where - "--report=conflict-path" reports each path to a conflict - state. +XML output for GNU Bison and gcc + http://www.cs.may.ie/~jpower/Research/bisonXML/ - (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. :-) +XML output for GNU Bison + http://yaxx.sourceforge.net/ -To implement this, see in the Fileutils the latest versions of -argmatch and so forth. +* 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 @@ -159,262 +160,65 @@ 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. + 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. -* Unit rules -Maybe we could expand unit rules, i.e., transform +* Broken options ? +** %token-table +** Skeleton strategy +Must we keep %token-table? - exp: arith | bool; - arith: exp '+' exp; - bool: exp '&' exp; +* src/print_graph.c +Find the best graph parameters. -into +* BTYacc +See if we can integrate backtracking in Bison. Charles-Henri de +Boysson 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. - exp: exp '+' exp | exp '&' exp; +** Keeping the conflicted actions +First, analyze the differences between byacc and btyacc (I'm referring +to the executables). Find where the conflicts are preserved. -when there are no actions. This can significantly speed up some -grammars. - -* 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. +** 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. -* --graph -Show reductions. [] +** Adjust the skeletons +Import the skeletons for C and C++. -* 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. [] +** Improve the skeletons +Have them support yysymprint, yydestruct and so forth. -* 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. - -* 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. -* BTYacc -See if we can integrate backtracking in Bison. Contact the BTYacc -maintainers. +* 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? -* Automaton report -Display more clearly the lookaheads for each item. +If there is really no profound motivation, we should find a new syntax +to allow specifying this. -* RR conflicts +** 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. - -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: @@ -424,6 +228,7 @@ 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 @@ -440,8 +245,6 @@ 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 @@ -453,6 +256,7 @@ 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 @@ -481,23 +285,25 @@ 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 Free Software Foundation, Inc. +Copyright (C) 2001, 2002, 2003, 2004, 2006 Free Software Foundation, +Inc. -This file is part of GNU Autoconf. +This file is part of Bison, the GNU Compiler Compiler. -GNU Autoconf 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 Autoconf 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. 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