| 1 | -*- outline -*- |
| 2 | |
| 3 | * Header guards |
| 4 | |
| 5 | From Franc,ois: should we keep the directory part in the CPP guard? |
| 6 | |
| 7 | |
| 8 | * Yacc.c: CPP Macros |
| 9 | |
| 10 | Do some people use YYPURE, YYLSP_NEEDED like we do in the test suite? |
| 11 | They should not: it is not documented. But if they need to, let's |
| 12 | find something clean (not like YYLSP_NEEDED...). |
| 13 | |
| 14 | |
| 15 | * Installation |
| 16 | |
| 17 | * Documentation |
| 18 | Before releasing, make sure the documentation ("Understanding your |
| 19 | parser") refers to the current `output' format. |
| 20 | |
| 21 | * lalr1.cc |
| 22 | ** vector |
| 23 | Move to using vector, drop stack.hh. |
| 24 | |
| 25 | ** I18n |
| 26 | Catch up with yacc.c. |
| 27 | |
| 28 | * Report |
| 29 | |
| 30 | ** GLR |
| 31 | How would Paul like to display the conflicted actions? In particular, |
| 32 | what when two reductions are possible on a given lookahead token, but one is |
| 33 | part of $default. Should we make the two reductions explicit, or just |
| 34 | keep $default? See the following point. |
| 35 | |
| 36 | ** Disabled Reductions |
| 37 | See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide |
| 38 | what we want to do. |
| 39 | |
| 40 | ** Documentation |
| 41 | Extend with error productions. The hard part will probably be finding |
| 42 | the right rule so that a single state does not exhibit too many yet |
| 43 | undocumented ``features''. Maybe an empty action ought to be |
| 44 | presented too. Shall we try to make a single grammar with all these |
| 45 | features, or should we have several very small grammars? |
| 46 | |
| 47 | ** --report=conflict-path |
| 48 | Provide better assistance for understanding the conflicts by providing |
| 49 | a sample text exhibiting the (LALR) ambiguity. See the paper from |
| 50 | DeRemer and Penello: they already provide the algorithm. |
| 51 | |
| 52 | ** Statically check for potential ambiguities in GLR grammars. See |
| 53 | <http://www.i3s.unice.fr/~schmitz/papers.html#expamb> for an approach. |
| 54 | |
| 55 | |
| 56 | * Extensions |
| 57 | |
| 58 | ** Labeling the symbols |
| 59 | Have a look at the Lemon parser generator: instead of $1, $2 etc. they |
| 60 | can name the values. This is much more pleasant. For instance: |
| 61 | |
| 62 | exp (res): exp (a) '+' exp (b) { $res = $a + $b; }; |
| 63 | |
| 64 | I love this. I have been bitten too often by the removal of the |
| 65 | symbol, and forgetting to shift all the $n to $n-1. If you are |
| 66 | unlucky, it compiles... |
| 67 | |
| 68 | But instead of using $a etc., we can use regular variables. And |
| 69 | instead of using (), I propose to use `:' (again). Paul suggests |
| 70 | supporting `->' in addition to `:' to separate LHS and RHS. In other |
| 71 | words: |
| 72 | |
| 73 | r:exp -> a:exp '+' b:exp { r = a + b; }; |
| 74 | |
| 75 | That requires an significant improvement of the grammar parser. Using |
| 76 | GLR would be nice. It also requires that Bison know the type of the |
| 77 | symbols (which will be useful for %include anyway). So we have some |
| 78 | time before... |
| 79 | |
| 80 | Note that there remains the problem of locations: `@r'? |
| 81 | |
| 82 | |
| 83 | ** $-1 |
| 84 | We should find a means to provide an access to values deep in the |
| 85 | stack. For instance, instead of |
| 86 | |
| 87 | baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; } |
| 88 | |
| 89 | we should be able to have: |
| 90 | |
| 91 | foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } |
| 92 | |
| 93 | Or something like this. |
| 94 | |
| 95 | ** %if and the like |
| 96 | It should be possible to have %if/%else/%endif. The implementation is |
| 97 | not clear: should it be lexical or syntactic. Vadim Maslow thinks it |
| 98 | must be in the scanner: we must not parse what is in a switched off |
| 99 | part of %if. Akim Demaille thinks it should be in the parser, so as |
| 100 | to avoid falling into another CPP mistake. |
| 101 | |
| 102 | ** -D, --define-muscle NAME=VALUE |
| 103 | To define muscles via cli. Or maybe support directly NAME=VALUE? |
| 104 | |
| 105 | ** XML Output |
| 106 | There are couple of available extensions of Bison targeting some XML |
| 107 | output. Some day we should consider including them. One issue is |
| 108 | that they seem to be quite orthogonal to the parsing technique, and |
| 109 | seem to depend mostly on the possibility to have some code triggered |
| 110 | for each reduction. As a matter of fact, such hooks could also be |
| 111 | used to generate the yydebug traces. Some generic scheme probably |
| 112 | exists in there. |
| 113 | |
| 114 | XML output for GNU Bison and gcc |
| 115 | http://www.cs.may.ie/~jpower/Research/bisonXML/ |
| 116 | |
| 117 | XML output for GNU Bison |
| 118 | http://yaxx.sourceforge.net/ |
| 119 | |
| 120 | * Unit rules |
| 121 | Maybe we could expand unit rules, i.e., transform |
| 122 | |
| 123 | exp: arith | bool; |
| 124 | arith: exp '+' exp; |
| 125 | bool: exp '&' exp; |
| 126 | |
| 127 | into |
| 128 | |
| 129 | exp: exp '+' exp | exp '&' exp; |
| 130 | |
| 131 | when there are no actions. This can significantly speed up some |
| 132 | grammars. I can't find the papers. In particular the book `LR |
| 133 | parsing: Theory and Practice' is impossible to find, but according to |
| 134 | `Parsing Techniques: a Practical Guide', it includes information about |
| 135 | this issue. Does anybody have it? |
| 136 | |
| 137 | |
| 138 | |
| 139 | * Documentation |
| 140 | |
| 141 | ** History/Bibliography |
| 142 | Some history of Bison and some bibliography would be most welcome. |
| 143 | Are there any Texinfo standards for bibliography? |
| 144 | |
| 145 | |
| 146 | |
| 147 | * Java, Fortran, etc. |
| 148 | |
| 149 | |
| 150 | * Coding system independence |
| 151 | Paul notes: |
| 152 | |
| 153 | Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is |
| 154 | 255). It also assumes that the 8-bit character encoding is |
| 155 | the same for the invocation of 'bison' as it is for the |
| 156 | invocation of 'cc', but this is not necessarily true when |
| 157 | people run bison on an ASCII host and then use cc on an EBCDIC |
| 158 | host. I don't think these topics are worth our time |
| 159 | addressing (unless we find a gung-ho volunteer for EBCDIC or |
| 160 | PDP-10 ports :-) but they should probably be documented |
| 161 | somewhere. |
| 162 | |
| 163 | More importantly, Bison does not currently allow NUL bytes in |
| 164 | tokens, either via escapes (e.g., "x\0y") or via a NUL byte in |
| 165 | the source code. This should get fixed. |
| 166 | |
| 167 | * --graph |
| 168 | Show reductions. |
| 169 | |
| 170 | * Broken options ? |
| 171 | ** %token-table |
| 172 | ** Skeleton strategy |
| 173 | Must we keep %token-table? |
| 174 | |
| 175 | * src/print_graph.c |
| 176 | Find the best graph parameters. |
| 177 | |
| 178 | * BTYacc |
| 179 | See if we can integrate backtracking in Bison. Charles-Henri de |
| 180 | Boysson <de-boy_c@epita.fr> is working on this, and already has some |
| 181 | results. Vadim Maslow, the maintainer of BTYacc was contacted, and we |
| 182 | stay in touch with him. Adjusting the Bison grammar parser will be |
| 183 | needed to support some extra BTYacc features. This is less urgent. |
| 184 | |
| 185 | ** Keeping the conflicted actions |
| 186 | First, analyze the differences between byacc and btyacc (I'm referring |
| 187 | to the executables). Find where the conflicts are preserved. |
| 188 | |
| 189 | ** Compare with the GLR tables |
| 190 | See how isomorphic the way BTYacc and the way the GLR adjustments in |
| 191 | Bison are compatible. *As much as possible* one should try to use the |
| 192 | same implementation in the Bison executables. I insist: it should be |
| 193 | very feasible to use the very same conflict tables. |
| 194 | |
| 195 | ** Adjust the skeletons |
| 196 | Import the skeletons for C and C++. |
| 197 | |
| 198 | ** Improve the skeletons |
| 199 | Have them support yysymprint, yydestruct and so forth. |
| 200 | |
| 201 | |
| 202 | * Precedence |
| 203 | |
| 204 | ** Partial order |
| 205 | It is unfortunate that there is a total order for precedence. It |
| 206 | makes it impossible to have modular precedence information. We should |
| 207 | move to partial orders (sounds like series/parallel orders to me). |
| 208 | |
| 209 | ** Correlation b/w precedence and associativity |
| 210 | Also, I fail to understand why we have to assign the same |
| 211 | associativity to operators with the same precedence. For instance, |
| 212 | why can't I decide that the precedence of * and / is the same, but the |
| 213 | latter is nonassoc? |
| 214 | |
| 215 | If there is really no profound motivation, we should find a new syntax |
| 216 | to allow specifying this. |
| 217 | |
| 218 | ** RR conflicts |
| 219 | See if we can use precedence between rules to solve RR conflicts. See |
| 220 | what POSIX says. |
| 221 | |
| 222 | |
| 223 | * $undefined |
| 224 | From Hans: |
| 225 | - If the Bison generated parser experiences an undefined number in the |
| 226 | character range, that character is written out in diagnostic messages, an |
| 227 | addition to the $undefined value. |
| 228 | |
| 229 | Suggest: Change the name $undefined to undefined; looks better in outputs. |
| 230 | |
| 231 | |
| 232 | * Default Action |
| 233 | From Hans: |
| 234 | - For use with my C++ parser, I transported the "switch (yyn)" statement |
| 235 | that Bison writes to the bison.simple skeleton file. This way, I can remove |
| 236 | the current default rule $$ = $1 implementation, which causes a double |
| 237 | assignment to $$ which may not be OK under C++, replacing it with a |
| 238 | "default:" part within the switch statement. |
| 239 | |
| 240 | Note that the default rule $$ = $1, when typed, is perfectly OK under C, |
| 241 | but in the C++ implementation I made, this rule is different from |
| 242 | $<type_name>$ = $<type_name>1. I therefore think that one should implement |
| 243 | a Bison option where every typed default rule is explicitly written out |
| 244 | (same typed ruled can of course be grouped together). |
| 245 | |
| 246 | Note: Robert Anisko handles this. He knows how to do it. |
| 247 | |
| 248 | |
| 249 | * Warnings |
| 250 | It would be nice to have warning support. See how Autoconf handles |
| 251 | them, it is fairly well described there. It would be very nice to |
| 252 | implement this in such a way that other programs could use |
| 253 | lib/warnings.[ch]. |
| 254 | |
| 255 | Don't work on this without first announcing you do, as I already have |
| 256 | thought about it, and know many of the components that can be used to |
| 257 | implement it. |
| 258 | |
| 259 | |
| 260 | * Pre and post actions. |
| 261 | From: Florian Krohm <florian@edamail.fishkill.ibm.com> |
| 262 | Subject: YYACT_EPILOGUE |
| 263 | To: bug-bison@gnu.org |
| 264 | X-Sent: 1 week, 4 days, 14 hours, 38 minutes, 11 seconds ago |
| 265 | |
| 266 | The other day I had the need for explicitly building the parse tree. I |
| 267 | used %locations for that and defined YYLLOC_DEFAULT to call a function |
| 268 | that returns the tree node for the production. Easy. But I also needed |
| 269 | to assign the S-attribute to the tree node. That cannot be done in |
| 270 | YYLLOC_DEFAULT, because it is invoked before the action is executed. |
| 271 | The way I solved this was to define a macro YYACT_EPILOGUE that would |
| 272 | be invoked after the action. For reasons of symmetry I also added |
| 273 | YYACT_PROLOGUE. Although I had no use for that I can envision how it |
| 274 | might come in handy for debugging purposes. |
| 275 | All is needed is to add |
| 276 | |
| 277 | #if YYLSP_NEEDED |
| 278 | YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen)); |
| 279 | #else |
| 280 | YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen); |
| 281 | #endif |
| 282 | |
| 283 | at the proper place to bison.simple. Ditto for YYACT_PROLOGUE. |
| 284 | |
| 285 | I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE |
| 286 | to bison. If you're interested, I'll work on a patch. |
| 287 | |
| 288 | * Better graphics |
| 289 | Equip the parser with a means to create the (visual) parse tree. |
| 290 | |
| 291 | ----- |
| 292 | |
| 293 | Copyright (C) 2001, 2002, 2003, 2004, 2006 Free Software Foundation, |
| 294 | Inc. |
| 295 | |
| 296 | This file is part of Bison, the GNU Compiler Compiler. |
| 297 | |
| 298 | This program is free software: you can redistribute it and/or modify |
| 299 | it under the terms of the GNU General Public License as published by |
| 300 | the Free Software Foundation, either version 3 of the License, or |
| 301 | (at your option) any later version. |
| 302 | |
| 303 | This program is distributed in the hope that it will be useful, |
| 304 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 305 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 306 | GNU General Public License for more details. |
| 307 | |
| 308 | You should have received a copy of the GNU General Public License |
| 309 | along with this program. If not, see <http://www.gnu.org/licenses/>. |