Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 1 | * Short term |
| 2 | ** Graphviz display code thoughts |
| 3 | The code for the --graph option is over two files: print_graph, and |
| 4 | graphviz. I believe this is because Bison used to also produce VCG graphs, |
| 5 | but since this is no longer true, maybe we could consider these files for |
| 6 | fusion. |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 7 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 8 | Little effort factoring seems to have been given to factoring in these files, |
| 9 | and their print-xml and print counterpart. We would very much like to re-use |
| 10 | the pretty format of states from .output in the .dot |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 11 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 12 | Also, the underscore in print_graph.[ch] isn't very fitting considering |
| 13 | the dashes in the other filenames. |
| 14 | |
| 15 | ** Variable names. |
| 16 | What should we name `variant' and `lex_symbol'? |
| 17 | |
| 18 | ** Use b4_symbol in all the skeleton |
| 19 | Move its definition in the more standard places and deploy it in other |
| 20 | skeletons. Then remove the older system, including the tables |
| 21 | generated by output.c |
| 22 | |
| 23 | ** Update the documentation on gnu.org |
| 24 | |
| 25 | ** Get rid of fake #lines [Bison: ...] |
| 26 | Possibly as simple as checking whether the column number is nonnegative. |
| 27 | |
| 28 | I have seen messages like the following from GCC. |
| 29 | |
| 30 | <built-in>:0: fatal error: opening dependency file .deps/libltdl/argz.Tpo: No such file or directory |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 31 | |
| 32 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 33 | ** Discuss about %printer/%destroy in the case of C++. |
| 34 | It would be very nice to provide the symbol classes with an operator<< |
| 35 | and a destructor. Unfortunately the syntax we have chosen for |
| 36 | %destroy and %printer make them hard to reuse. For instance, the user |
| 37 | is invited to write something like |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 38 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 39 | %printer { debug_stream() << $$; } <my_type>; |
| 40 | |
| 41 | which is hard to reuse elsewhere since it wants to use |
| 42 | "debug_stream()" to find the stream to use. The same applies to |
| 43 | %destroy: we told the user she could use the members of the Parser |
| 44 | class in the printers/destructors, which is not good for an operator<< |
| 45 | since it is no longer bound to a particular parser, it's just a |
| 46 | (standalone symbol). |
| 47 | |
| 48 | ** Rename LR0.cc |
| 49 | as lr0.cc, why upper case? |
| 50 | |
| 51 | ** bench several bisons. |
| 52 | Enhance bench.pl with %b to run different bisons. |
| 53 | |
| 54 | * Various |
| 55 | ** Warnings |
| 56 | Warnings about type tags that are used in printer and dtors, but not |
| 57 | for symbols? |
| 58 | |
| 59 | ** YYERRCODE |
| 60 | Defined to 256, but not used, not documented. Probably the token |
| 61 | number for the error token, which POSIX wants to be 256, but which |
| 62 | Bison might renumber if the user used number 256. Keep fix and doc? |
| 63 | Throw away? |
| 64 | |
| 65 | Also, why don't we output the token name of the error token in the |
| 66 | output? It is explicitly skipped: |
| 67 | |
| 68 | /* Skip error token and tokens without identifier. */ |
| 69 | if (sym != errtoken && id) |
| 70 | |
| 71 | Of course there are issues with name spaces, but if we disable we have |
| 72 | something which seems to be more simpler and more consistent instead |
| 73 | of the special case YYERRCODE. |
| 74 | |
| 75 | enum yytokentype { |
| 76 | error = 256, |
| 77 | // ... |
| 78 | }; |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 79 | |
| 80 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 81 | We could (should?) also treat the case of the undef_token, which is |
| 82 | numbered 257 for yylex, and 2 internal. Both appear for instance in |
| 83 | toknum: |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 84 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 85 | const unsigned short int |
| 86 | parser::yytoken_number_[] = |
| 87 | { |
| 88 | 0, 256, 257, 258, 259, 260, 261, 262, 263, 264, |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 89 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 90 | while here |
| 91 | |
| 92 | enum yytokentype { |
| 93 | TOK_EOF = 0, |
| 94 | TOK_EQ = 258, |
| 95 | |
| 96 | so both 256 and 257 are "mysterious". |
| 97 | |
| 98 | const char* |
| 99 | const parser::yytname_[] = |
| 100 | { |
| 101 | "\"end of command\"", "error", "$undefined", "\"=\"", "\"break\"", |
| 102 | |
| 103 | |
| 104 | ** YYFAIL |
| 105 | It is seems to be *really* obsolete now, shall we remove it? |
| 106 | |
| 107 | ** yychar == yyempty_ |
| 108 | The code in yyerrlab reads: |
| 109 | |
| 110 | if (yychar <= YYEOF) |
| 111 | { |
| 112 | /* Return failure if at end of input. */ |
| 113 | if (yychar == YYEOF) |
| 114 | YYABORT; |
| 115 | } |
| 116 | |
| 117 | There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF. |
| 118 | But I can't produce the situation where yychar is YYEMPTY here, is it |
| 119 | really possible? The test suite does not exercise this case. |
| 120 | |
| 121 | This shows that it would be interesting to manage to install skeleton |
| 122 | coverage analysis to the test suite. |
| 123 | |
| 124 | ** Table definitions |
| 125 | It should be very easy to factor the definition of the various tables, |
| 126 | including the separation bw declaration and definition. See for |
| 127 | instance b4_table_define in lalr1.cc. This way, we could even factor |
| 128 | C vs. C++ definitions. |
| 129 | |
| 130 | * From lalr1.cc to yacc.c |
| 131 | ** Single stack |
| 132 | Merging the three stacks in lalr1.cc simplified the code, prompted for |
| 133 | other improvements and also made it faster (probably because memory |
| 134 | management is performed once instead of three times). I suggest that |
| 135 | we do the same in yacc.c. |
| 136 | |
| 137 | ** yysyntax_error |
| 138 | The code bw glr.c and yacc.c is really alike, we can certainly factor |
| 139 | some parts. |
| 140 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 141 | |
| 142 | * Report |
| 143 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 144 | ** Figures |
| 145 | Some statistics about the grammar and the parser would be useful, |
| 146 | especially when asking the user to send some information about the |
| 147 | grammars she is working on. We should probably also include some |
| 148 | information about the variables (I'm not sure for instance we even |
| 149 | specify what LR variant was used). |
| 150 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 151 | ** GLR |
| 152 | How would Paul like to display the conflicted actions? In particular, |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 153 | what when two reductions are possible on a given lookahead token, but one is |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 154 | part of $default. Should we make the two reductions explicit, or just |
| 155 | keep $default? See the following point. |
| 156 | |
| 157 | ** Disabled Reductions |
| 158 | See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide |
| 159 | what we want to do. |
| 160 | |
| 161 | ** Documentation |
| 162 | Extend with error productions. The hard part will probably be finding |
| 163 | the right rule so that a single state does not exhibit too many yet |
| 164 | undocumented ``features''. Maybe an empty action ought to be |
| 165 | presented too. Shall we try to make a single grammar with all these |
| 166 | features, or should we have several very small grammars? |
| 167 | |
| 168 | ** --report=conflict-path |
| 169 | Provide better assistance for understanding the conflicts by providing |
| 170 | a sample text exhibiting the (LALR) ambiguity. See the paper from |
| 171 | DeRemer and Penello: they already provide the algorithm. |
| 172 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 173 | ** Statically check for potential ambiguities in GLR grammars. See |
| 174 | <http://www.i3s.unice.fr/~schmitz/papers.html#expamb> for an approach. |
| 175 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 176 | |
| 177 | * Extensions |
| 178 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 179 | ** $-1 |
| 180 | We should find a means to provide an access to values deep in the |
| 181 | stack. For instance, instead of |
| 182 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 183 | baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; } |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 184 | |
| 185 | we should be able to have: |
| 186 | |
| 187 | foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } |
| 188 | |
| 189 | Or something like this. |
| 190 | |
| 191 | ** %if and the like |
| 192 | It should be possible to have %if/%else/%endif. The implementation is |
| 193 | not clear: should it be lexical or syntactic. Vadim Maslow thinks it |
| 194 | must be in the scanner: we must not parse what is in a switched off |
| 195 | part of %if. Akim Demaille thinks it should be in the parser, so as |
| 196 | to avoid falling into another CPP mistake. |
| 197 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 198 | ** XML Output |
| 199 | There are couple of available extensions of Bison targeting some XML |
| 200 | output. Some day we should consider including them. One issue is |
| 201 | that they seem to be quite orthogonal to the parsing technique, and |
| 202 | seem to depend mostly on the possibility to have some code triggered |
| 203 | for each reduction. As a matter of fact, such hooks could also be |
| 204 | used to generate the yydebug traces. Some generic scheme probably |
| 205 | exists in there. |
| 206 | |
| 207 | XML output for GNU Bison and gcc |
| 208 | http://www.cs.may.ie/~jpower/Research/bisonXML/ |
| 209 | |
| 210 | XML output for GNU Bison |
| 211 | http://yaxx.sourceforge.net/ |
| 212 | |
| 213 | * Unit rules |
| 214 | Maybe we could expand unit rules, i.e., transform |
| 215 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 216 | exp: arith | bool; |
| 217 | arith: exp '+' exp; |
| 218 | bool: exp '&' exp; |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 219 | |
| 220 | into |
| 221 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 222 | exp: exp '+' exp | exp '&' exp; |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 223 | |
| 224 | when there are no actions. This can significantly speed up some |
| 225 | grammars. I can't find the papers. In particular the book `LR |
| 226 | parsing: Theory and Practice' is impossible to find, but according to |
| 227 | `Parsing Techniques: a Practical Guide', it includes information about |
| 228 | this issue. Does anybody have it? |
| 229 | |
| 230 | |
| 231 | |
| 232 | * Documentation |
| 233 | |
| 234 | ** History/Bibliography |
| 235 | Some history of Bison and some bibliography would be most welcome. |
| 236 | Are there any Texinfo standards for bibliography? |
| 237 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 238 | * Coding system independence |
| 239 | Paul notes: |
| 240 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 241 | Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is |
| 242 | 255). It also assumes that the 8-bit character encoding is |
| 243 | the same for the invocation of 'bison' as it is for the |
| 244 | invocation of 'cc', but this is not necessarily true when |
| 245 | people run bison on an ASCII host and then use cc on an EBCDIC |
| 246 | host. I don't think these topics are worth our time |
| 247 | addressing (unless we find a gung-ho volunteer for EBCDIC or |
| 248 | PDP-10 ports :-) but they should probably be documented |
| 249 | somewhere. |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 250 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 251 | More importantly, Bison does not currently allow NUL bytes in |
| 252 | tokens, either via escapes (e.g., "x\0y") or via a NUL byte in |
| 253 | the source code. This should get fixed. |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 254 | |
| 255 | * --graph |
| 256 | Show reductions. |
| 257 | |
| 258 | * Broken options ? |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 259 | ** %token-table |
| 260 | ** Skeleton strategy |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 261 | Must we keep %token-table? |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 262 | |
| 263 | * Precedence |
| 264 | |
| 265 | ** Partial order |
| 266 | It is unfortunate that there is a total order for precedence. It |
| 267 | makes it impossible to have modular precedence information. We should |
| 268 | move to partial orders (sounds like series/parallel orders to me). |
| 269 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 270 | ** RR conflicts |
| 271 | See if we can use precedence between rules to solve RR conflicts. See |
| 272 | what POSIX says. |
| 273 | |
| 274 | |
| 275 | * $undefined |
| 276 | From Hans: |
| 277 | - If the Bison generated parser experiences an undefined number in the |
| 278 | character range, that character is written out in diagnostic messages, an |
| 279 | addition to the $undefined value. |
| 280 | |
| 281 | Suggest: Change the name $undefined to undefined; looks better in outputs. |
| 282 | |
| 283 | |
| 284 | * Default Action |
| 285 | From Hans: |
| 286 | - For use with my C++ parser, I transported the "switch (yyn)" statement |
| 287 | that Bison writes to the bison.simple skeleton file. This way, I can remove |
| 288 | the current default rule $$ = $1 implementation, which causes a double |
| 289 | assignment to $$ which may not be OK under C++, replacing it with a |
| 290 | "default:" part within the switch statement. |
| 291 | |
| 292 | Note that the default rule $$ = $1, when typed, is perfectly OK under C, |
| 293 | but in the C++ implementation I made, this rule is different from |
| 294 | $<type_name>$ = $<type_name>1. I therefore think that one should implement |
| 295 | a Bison option where every typed default rule is explicitly written out |
| 296 | (same typed ruled can of course be grouped together). |
| 297 | |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 298 | * Pre and post actions. |
| 299 | From: Florian Krohm <florian@edamail.fishkill.ibm.com> |
| 300 | Subject: YYACT_EPILOGUE |
| 301 | To: bug-bison@gnu.org |
| 302 | X-Sent: 1 week, 4 days, 14 hours, 38 minutes, 11 seconds ago |
| 303 | |
| 304 | The other day I had the need for explicitly building the parse tree. I |
| 305 | used %locations for that and defined YYLLOC_DEFAULT to call a function |
| 306 | that returns the tree node for the production. Easy. But I also needed |
| 307 | to assign the S-attribute to the tree node. That cannot be done in |
| 308 | YYLLOC_DEFAULT, because it is invoked before the action is executed. |
| 309 | The way I solved this was to define a macro YYACT_EPILOGUE that would |
| 310 | be invoked after the action. For reasons of symmetry I also added |
| 311 | YYACT_PROLOGUE. Although I had no use for that I can envision how it |
| 312 | might come in handy for debugging purposes. |
| 313 | All is needed is to add |
| 314 | |
| 315 | #if YYLSP_NEEDED |
| 316 | YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen)); |
| 317 | #else |
| 318 | YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen); |
| 319 | #endif |
| 320 | |
| 321 | at the proper place to bison.simple. Ditto for YYACT_PROLOGUE. |
| 322 | |
| 323 | I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE |
| 324 | to bison. If you're interested, I'll work on a patch. |
| 325 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 326 | * Better graphics |
| 327 | Equip the parser with a means to create the (visual) parse tree. |
| 328 | |
| 329 | * Complaint submessage indentation. |
| 330 | We already have an implementation that works fairly well for named |
| 331 | reference messages, but it would be nice to use it consistently for all |
| 332 | submessages from Bison. For example, the "previous definition" |
| 333 | submessage or the list of correct values for a %define variable might |
| 334 | look better with indentation. |
| 335 | |
| 336 | However, the current implementation makes the assumption that the |
| 337 | location printed on the first line is not usually much shorter than the |
| 338 | locations printed on the submessage lines that follow. That assumption |
| 339 | may not hold true as often for some kinds of submessages especially if |
| 340 | we ever support multiple grammar files. |
| 341 | |
| 342 | Here's a proposal for how a new implementation might look: |
| 343 | |
| 344 | http://lists.gnu.org/archive/html/bison-patches/2009-09/msg00086.html |
| 345 | |
| 346 | |
| 347 | Local Variables: |
| 348 | mode: outline |
| 349 | coding: utf-8 |
| 350 | End: |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 351 | |
| 352 | ----- |
| 353 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 354 | Copyright (C) 2001-2004, 2006, 2008-2012 Free Software Foundation, Inc. |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 355 | |
| 356 | This file is part of Bison, the GNU Compiler Compiler. |
| 357 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 358 | This program is free software: you can redistribute it and/or modify |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 359 | it under the terms of the GNU General Public License as published by |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 360 | the Free Software Foundation, either version 3 of the License, or |
| 361 | (at your option) any later version. |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 362 | |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 363 | This program is distributed in the hope that it will be useful, |
The Android Open Source Project | cea198a | 2009-03-03 19:29:17 -0800 | [diff] [blame] | 364 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 365 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 366 | GNU General Public License for more details. |
| 367 | |
| 368 | You should have received a copy of the GNU General Public License |
Ying Wang | 0543663 | 2013-04-05 16:01:00 -0700 | [diff] [blame] | 369 | along with this program. If not, see <http://www.gnu.org/licenses/>. |