NG4R3P

Linux 4gvps.4gvps.com 3.10.0-1127.18.2.vz7.163.46 #1 SMP Fri Nov 20 21:47:55 MSK 2020 x86_64
SOFT : Apache PHP : 7.4.33
/proc/self/root/usr/share/doc/bison-3.0.4/

38.135.39.45

[ NAME ]	[ SIZE ]	[ PERM ]	[ DATE ]	[ ACT ]
+FILE +DIR
AUTHORS	1.426 KB	-rw-r--r--	2015-01-16 14:47	R E G D
COPYING	34.323 KB	-rw-r--r--	2013-02-16 13:16	R E G D
ChangeLog	347.122 KB	-rw-r--r--	2015-01-23 13:13	R E G D
NEWS	98.252 KB	-rw-r--r--	2015-01-23 12:53	R E G D
README	2.235 KB	-rw-r--r--	2015-01-16 14:47	R E G D
THANKS	8.408 KB	-rw-r--r--	2015-01-18 14:15	R E G D
TODO	13.81 KB	-rw-r--r--	2015-01-16 14:47	R E G D
REQUEST EXIT

* Short term ** Graphviz display code thoughts The code for the --graph option is over two files: print_graph, and graphviz. This is because Bison used to also produce VCG graphs, but since this is no longer true, maybe we could consider these files for fusion. An other consideration worth noting is that print_graph.c (correct me if I am wrong) should contain generic functions, whereas graphviz.c and other potential files should contain just the specific code for that output format. It will probably prove difficult to tell if the implementation is actually generic whilst only having support for a single format, but it would be nice to keep stuff a bit tidier: right now, the construction of the bitset used to show reductions is in the graphviz-specific code, and on the opposite side we have some use of \l, which is graphviz-specific, in what should be generic code. Little effort seems to have been given to factoring these files and their rint{,-xml} counterpart. We would very much like to re-use the pretty format of states from .output for the graphs, etc. Also, the underscore in print_graph.[ch] isn't very fitting considering the dashes in the other filenames. Since graphviz dies on medium-to-big grammars, maybe consider an other tool? ** push-parser Check it too when checking the different kinds of parsers. And be sure to check that the initial-action is performed once per parsing. ** m4 names b4_shared_declarations is no longer what it is. Make it b4_parser_declaration for instance. ** yychar in lalr1.cc There is a large difference bw maint and master on the handling of yychar (which was removed in lalr1.cc). See what needs to be back-ported. /* User semantic actions sometimes alter yychar, and that requires that yytoken be updated with the new translation. We take the approach of translating immediately before every use of yytoken. One alternative is translating here after every semantic action, but that translation would be missed if the semantic action invokes YYABORT, YYACCEPT, or YYERROR immediately after altering yychar. In the case of YYABORT or YYACCEPT, an incorrect destructor might then be invoked immediately. In the case of YYERROR, subsequent parser actions might lead to an incorrect destructor call or verbose syntax error message before the lookahead is translated. */ /* Make sure we have latest lookahead translation. See comments at user semantic actions for why this is necessary. */ yytoken = yytranslate_ (yychar); ** stack.hh Get rid of it. The original idea is nice, but actually it makes the code harder to follow, and uselessly different from the other skeletons. ** 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? * Various ** 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\"", ** 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. * 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. * 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 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 ** $-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 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? * 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. * Broken options ? ** %token-table ** Skeleton strategy Must we keep %token-table? * 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). ** 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. * Complaint submessage indentation. We already have an implementation that works fairly well for named reference messages, but it would be nice to use it consistently for all submessages from Bison. For example, the "previous definition" submessage or the list of correct values for a %define variable might look better with indentation. However, the current implementation makes the assumption that the location printed on the first line is not usually much shorter than the locations printed on the submessage lines that follow. That assumption may not hold true as often for some kinds of submessages especially if we ever support multiple grammar files. Here's a proposal for how a new implementation might look: http://lists.gnu.org/archive/html/bison-patches/2009-09/msg00086.html Local Variables: mode: outline coding: utf-8 End: ----- Copyright (C) 2001-2004, 2006, 2008-2015 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. You should have received a copy of the GNU General Public License along with this program. If not, see .