X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/0e95c1ddc133e6ccb7fd31514a39e0f4204a9080..fe1b448ada5e3a79ae3f523e08b5004396f30ca9:/TODO diff --git a/TODO b/TODO index 02f6b15b..e42c4b5c 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,234 @@ -*- outline -*- +* Various +** YYPRINT +glr.c inherits its symbol_print function from c.m4, which supports +YYPRINT. But to use YYPRINT yytoknum is needed, which not defined by +glr.c. + +Anyway, IMHO YYPRINT is obsolete and should be restricted to yacc.c. + +** YYERRCODE +Defined to 256, but not used, not documented.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? + +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: + + const unsigned short int + parser::yytoken_number_[] = + { + 0, 256, 257, 258, 259, 260, 261, 262, 263, 264, + +while here + + 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\"", + + +** YYFAIL +It is seems to be *really* obsolete now, shall we remove it? + +** YYBACKUP +There is no test about it, no examples in the doc, and I'm not sure +what it should look like. For instance what follows crashes. + + %error-verbose + %debug + %pure-parser + %code { + # include + # include + # include + + static void yyerror (const char *msg); + static int yylex (YYSTYPE *yylval); + } + %% + exp: + 'a' { printf ("a: %d\n", $1); } + | 'b' { YYBACKUP('a', 123); } + ; + %% + static int + yylex (YYSTYPE *yylval) + { + static char const input[] = "b"; + static size_t toknum; + assert (toknum < sizeof input); + *yylval = (toknum + 1) * 10; + return input[toknum++]; + } + + static void + yyerror (const char *msg) + { + fprintf (stderr, "%s\n", msg); + } + + int + main (void) + { + yydebug = !!getenv("YYDEBUG"); + return yyparse (); + } + +** 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. + +** Table definitions +It should be very easy to factor the definition of the various tables, +including the separation bw declaration and definition. See for +instance b4_table_define in lalr1.cc. This way, we could even factor +C vs. C++ definitions. + +* 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 +In lalr1.cc we invoke it with the translated lookahead (yytoken), and +yacc.c uses yychar. I don't see why. + +** yysyntax_error +The use of switch to select yyfmt in lalr1.cc seems simpler than +what's done in yacc.c. + +* Header guards + +From Franc,ois: should we keep the directory part in the CPP guard? + + +* Yacc.c: CPP Macros + +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...). + + +* Installation + +* Documentation +Before releasing, make sure the documentation ("Understanding your +parser") refers to the current `output' format. + +* Report + +** 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. + +** Disabled Reductions +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 +presented too. Shall we try to make a single grammar with all these +features, or should we have several very small grammars? + +** --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. + +** Statically check for potential ambiguities in GLR grammars. See + for an approach. + + +* Extensions + +** 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: + + exp (res): exp (a) '+' exp (b) { $res = $a + $b; }; + +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... + +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: + + r:exp -> a:exp '+' b:exp { r = a + b; }; + +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... + +Note that there remains the problem of locations: `@r'? + + +** $-1 +We should find a means to provide an access to values deep in the +stack. For instance, instead of + + baz: qux { $$ = $-1 + $0 + $1; } + +we should be able to have: + + foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } + +Or something like this. + +** %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 @@ -12,156 +241,154 @@ into exp: exp '+' exp | exp '&' exp; 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! - -* 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. - -* 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; - } +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. - %{ - ... - 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. +* 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. + + 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. [] +Show reductions. * Broken options ? -** %no-lines [ok] -** %no-parser [] -** %pure-parser [] -** %semantic-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. - -* 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. +** %token-table +** Skeleton strategy +Must we keep %token-table? * BTYacc -See if we can integrate backtracking in Bison. Contact the BTYacc -maintainers. +See if we can integrate backtracking in Bison. Charles-Henri de +Boysson has been working on this, but never gave +the results. -* Automaton report -Display more clearly the lookaheads for each item. +Vadim Maslow, the maintainer of BTYacc was once contacted. Adjusting +the Bison grammar parser will be needed to support some extra BTYacc +features. This is less urgent. + +** 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 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. + +** Adjust the skeletons +Import the skeletons for C and C++. -* RR conflicts -See if we can use precedence between rules to solve RR conflicts. See -what POSIX says. * 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. +move to partial orders (sounds like series/parallel orders to me). + +** RR conflicts +See if we can use precedence between rules to solve RR conflicts. See +what POSIX says. + + +* $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. + +* Better graphics +Equip the parser with a means to create the (visual) parse tree. + +----- + +Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008 Free Software Foundation, +Inc. + +This file is part of Bison, the GNU Compiler Compiler. + +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 3 of the License, or +(at your option) any later version. + +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. -* Parsing grammars -Rewrite the reader in Bison. +You should have received a copy of the GNU General Public License +along with this program. If not, see .