X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/742e4900c8b05c8c1f56985288141c890f1e9c73..47eced3099712180364f4e01b839242027d9a9d8:/TODO diff --git a/TODO b/TODO index 96d5d2a4..c3aac317 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,201 @@ -*- outline -*- +* Short term +** Use syntax_error from the scanner? +This would provide a means to raise syntax error from function called +from the scanner. Actually, there is no good solution to report a +lexical error in general. Usually they are kept at the scanner level +only, ignoring the guilty token. But that might not be the best bet, +since we don't benefit from the syntactic error recovery. + +We still have the possibility to return an invalid token number, which +does the trick. But then the error message from the parser is poor +(something like "unexpected $undefined"). Since the scanner probably +already reported the error, we should directly enter error-recovery, +without reporting the error message (i.e., YYERROR's semantics). + +Back to lalr1.cc (whose name is now quite unfortunate, since it also +covers lr and ielr), if we support exceptions from yylex, should we +propose a lexical_error in addition to syntax_error? Should they have +a common root, say parse_error? Should syntax_error be renamed +syntactic_error for consistency with lexical_error? + +** Variable names. +What should we name `variant' and `lex_symbol'? + +** Use b4_symbol in all the skeleton +Then remove the older system, including the tables generated by +output.c + +** Update the documentation on gnu.org + +** 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). + +** 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? + +Also, why don't we output the token name of the error token in the +output? It is explicitly skipped: + + /* Skip error token and tokens without identifier. */ + if (sym != errtoken && id) + +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. + + enum yytokentype { + error = 256, + // ... + }; + + +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 +The code bw glr.c and yacc.c is really alike, we can certainly factor +some parts. + * Header guards From Franc,ois: should we keep the directory part in the CPP guard? @@ -14,26 +210,19 @@ find something clean (not like YYLSP_NEEDED...). * Installation -** Disable installation of yacc. - -Add an option to 'configure' that allows people to install Bison -without installing the yacc wrapper script or the rarely-used little -yacc library required by Posix. This is for people who prefer some -other implementation of yacc. - * Documentation Before releasing, make sure the documentation ("Understanding your parser") refers to the current `output' format. -* lalr1.cc -** vector -Move to using vector, drop stack.hh. - -** I18n -Catch up with yacc.c. - * 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 token, but one is @@ -56,6 +245,9 @@ 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 @@ -103,9 +295,6 @@ 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. -** -D, --define-muscle NAME=VALUE -To define muscles via cli. Or maybe support directly NAME=VALUE? - ** XML Output There are couple of available extensions of Bison targeting some XML output. Some day we should consider including them. One issue is @@ -146,28 +335,12 @@ this issue. Does anybody have it? Some history of Bison and some bibliography would be most welcome. Are there any Texinfo standards for bibliography? - +** %printer +Wow, %printer is not documented. Clearly mark YYPRINT as obsolete. * 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. - - -Sebastien 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: @@ -189,20 +362,18 @@ Paul notes: Show reductions. * Broken options ? -** %no-parser ** %token-table ** Skeleton strategy -Must we keep %no-parser? %token-table? - -* src/print_graph.c -Find the best graph parameters. +Must we keep %token-table? * 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. +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 @@ -217,9 +388,6 @@ 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 @@ -228,18 +396,6 @@ 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. @@ -268,20 +424,6 @@ $$ = $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 @@ -310,28 +452,25 @@ 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, 2003, 2004, 2006 Free Software Foundation, -Inc. +Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008-2009 Free Software +Foundation, Inc. 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