X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/d43baf71a71dc0fb20534f401d2b9bdfa6439927..d50eea6df5e4fff2ec4247e0faae009c53879404:/TODO diff --git a/TODO b/TODO index 599626f2..8343bbb3 100644 --- a/TODO +++ b/TODO @@ -1,47 +1,178 @@ -*- outline -*- -* Header guards - -From Franc,ois: should we keep the directory part in the CPP guard? +* Short term +** Document %define assert + +** 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). + +** Rename LR0.cc +as lr0.cc, why upper case? + +** bench several bisons. +Enhance bench.pl with %b to run different bisons. + +** Use b4_symbol everywhere. +Move its definition in the more standard places and deploy it in other +skeletons. + +* 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 But to use YYPRINT yytoknum is needed, which not defined by +glr.c. + +Anyway, IMHO YYPRINT is obsolete and should be restricted to yacc.c. + +** YYERRCODE +Defined to 256, but not used, not documented.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. -* URGENT: Documenting C++ output -Write a first documentation for C++ output. +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. -* Documentation -Before releasing, make sure the documentation refers to the current -`output' format. +* 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. -* Error messages -Some are really funky. For instance +** yysyntax_error +The use of switch to select yyfmt in lalr1.cc seems simpler than +what's done in yacc.c. - type clash (`%s' `%s') on default action - -is really weird. Revisit them all. +* Header guards +From Franc,ois: should we keep the directory part in the CPP guard? -* 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. +* Yacc.c: CPP Macros -* 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? +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...). -* GLR & C++ -Currently, the GLR parser cannot compile with a C++ compiler. +* 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, 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. @@ -61,34 +192,70 @@ 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 -** 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... +** 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: -** 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. + exp (res): exp (a) '+' exp (b) { $res = $a + $b; }; -When implementing multiple-%union support, bare the following in mind: +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... -- when --yacc, this must be flagged as an error. Don't make it fatal - though. +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: -- The #line must now appear *inside* the definition of yystype. - Something like + r:exp -> a:exp '+' b:exp { r = a + b; }; - { - #line 12 "foo.y" - int ival; - #line 23 "foo.y" - char *sval; - } +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 @@ -120,23 +287,6 @@ Are there any Texinfo standards for bibliography? * Java, Fortran, etc. -** Java - -There are a couple of proposed outputs: - -- BYACC/J - which is based on Byacc. - - -- Bison Java - which is based on Bison. - - -Sébastien Serrurier (serrur_s@epita.fr) is working on this: he is -expected to contact the authors, design the output, and implement it -into Bison. - - * Coding system independence Paul notes: @@ -150,49 +300,26 @@ Paul notes: 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 [] -** %token-table [] -** Options which could use parse_dquoted_param (). -Maybe transferred 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 explanations 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. +** %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. + +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 @@ -207,9 +334,6 @@ 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. - * Precedence @@ -218,18 +342,6 @@ 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. @@ -258,20 +370,6 @@ $$ = $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 @@ -300,27 +398,25 @@ 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. -* 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. ----- -Copyright (C) 2001, 2002 Free Software Foundation, Inc. +Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008 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 .