TODO

   1 -*- outline -*-
   2
   3 * URGENT: Documenting C++ output
   4 Write a first documentation for C++ output.
   5
   6
   7 * Documentation
   8 Before releasing, make sure the documentation refers to the current
   9 `output' format.
  10
  11
  12 * Error messages
  13 Some are really funky.  For instance
  14
  15         type clash (`%s' `%s') on default action
  16
  17 is really weird.  Revisit them all.
  18
  19
  20 * read_pipe.c
  21 This is not portable to DOS for instance.  Implement a more portable
  22 scheme.  Sources of inspiration include GNU diff, and Free Recode.
  23
  24
  25 * value_components_used
  26 Was defined but not used: where was it coming from?  It can't be to
  27 check if %union is used, since the user is free to $<foo>n on her
  28 union, doesn't she?
  29
  30
  31 * Report
  32
  33 **  GLR
  34 How would Paul like to display the conflicted actions?  In particular,
  35 what when two reductions are possible on a given lookahead, but one is
  36 part of $default.  Should we make the two reductions explicit, or just
  37 keep $default?  See the following point.
  38
  39 ** Disabled Reductions
  40 See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
  41 what we want to do.
  42
  43 ** Documentation
  44 Extend with error productions.  The hard part will probably be finding
  45 the right rule so that a single state does not exhibit too many yet
  46 undocumented ``features''.  Maybe an empty action ought to be
  47 presented too.  Shall we try to make a single grammar with all these
  48 features, or should we have several very small grammars?
  49
  50 ** --report=conflict-path
  51 Provide better assistance for understanding the conflicts by providing
  52 a sample text exhibiting the (LALR) ambiguity.  See the paper from
  53 DeRemer and Penello: they already provide the algorithm.
  54
  55
  56 * Extentions
  57
  58 ** yyerror, yysymprint interface
  59 It should be improved, in particular when using Bison features such as
  60 locations, and YYPARSE_PARAMS.  For the time being, it is recommended
  61 to #define yyerror and yyprint to steal internal variables...
  62
  63 ** Several %unions
  64 I think this is a pleasant (but useless currently) feature, but in the
  65 future, I want a means to %include other bits of grammars, and _then_
  66 it will be important for the various bits to define their needs in
  67 %union.
  68
  69 When implementing multiple-%union support, bare the following in mind:
  70
  71 - when --yacc, this must be flagged as an error.  Don't make it fatal
  72   though.
  73
  74 - The #line must now appear *inside* the definition of yystype.
  75   Something like
  76
  77         {
  78         #line 12 "foo.y"
  79           int ival;
  80         #line 23 "foo.y"
  81           char *sval;
  82         }
  83
  84 * Unit rules
  85 Maybe we could expand unit rules, i.e., transform
  86
  87         exp: arith | bool;
  88         arith: exp '+' exp;
  89         bool: exp '&' exp;
  90
  91 into
  92
  93         exp: exp '+' exp | exp '&' exp;
  94
  95 when there are no actions.  This can significantly speed up some
  96 grammars.  I can't find the papers.  In particular the book `LR
  97 parsing: Theory and Practice' is impossible to find, but according to
  98 `Parsing Techniques: a Practical Guide', it includes information about
  99 this issue.  Does anybody have it?
 100
 101
 102
 103 * Documentation
 104
 105 ** History/Bibliography
 106 Some history of Bison and some bibliography would be most welcome.
 107 Are there any Texinfo standards for bibliography?
 108
 109
 110
 111
 112 * Coding system independence
 113 Paul notes:
 114
 115         Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is
 116         255).  It also assumes that the 8-bit character encoding is
 117         the same for the invocation of 'bison' as it is for the
 118         invocation of 'cc', but this is not necessarily true when
 119         people run bison on an ASCII host and then use cc on an EBCDIC
 120         host.  I don't think these topics are worth our time
 121         addressing (unless we find a gung-ho volunteer for EBCDIC or
 122         PDP-10 ports :-) but they should probably be documented
 123         somewhere.
 124
 125
 126
 127 * --graph
 128 Show reductions.        []
 129
 130 * Broken options ?
 131 ** %no-lines            [ok]
 132 ** %no-parser           []
 133 ** %pure-parser         []
 134 ** %token-table         []
 135 ** Options which could use parse_dquoted_param ().
 136 Maybe transfered in lex.c.
 137 *** %skeleton           [ok]
 138 *** %output             []
 139 *** %file-prefix        []
 140 *** %name-prefix        []
 141
 142 ** Skeleton strategy.   []
 143 Must we keep %no-parser?
 144              %token-table?
 145 *** New skeletons.      []
 146
 147 * src/print_graph.c
 148 Find the best graph parameters. []
 149
 150 * doc/bison.texinfo
 151 ** Update
 152 informations about ERROR_VERBOSE.       []
 153 ** Add explainations about
 154 skeleton muscles.       []
 155 %skeleton.              []
 156
 157 * testsuite
 158 ** tests/pure-parser.at []
 159 New tests.
 160
 161 * input synclines
 162 Some users create their foo.y files, and equip them with #line.  Bison
 163 should recognize these, and preserve them.
 164
 165 * BTYacc
 166 See if we can integrate backtracking in Bison.  Contact the BTYacc
 167 maintainers.
 168
 169 ** Keeping the conflicted actions
 170 First, analyze the differences between byacc and btyacc (I'm referring
 171 to the executables).  Find where the conflicts are preserved.
 172
 173 ** Compare with the GLR tables
 174 See how isomorphic the way BTYacc and the way the GLR adjustements in
 175 Bison are compatible.  *As much as possible* one should try to use the
 176 same implementation in the Bison executables.  I insist: it should be
 177 very feasible to use the very same conflict tables.
 178
 179 ** Adjust the skeletons
 180 Import the skeletons for C and C++.
 181
 182 ** Improve the skeletons
 183 Have them support yysymprint, yydestruct and so forth.
 184
 185
 186 * Precedence
 187
 188 ** Partial order
 189 It is unfortunate that there is a total order for precedence.  It
 190 makes it impossible to have modular precedence information.  We should
 191 move to partial orders (sounds like series/parallel orders to me).
 192
 193 This will be possible with a Bison parser for the grammar, as it will
 194 make it much easier to extend the grammar.
 195
 196 ** Correlation b/w precedence and associativity
 197 Also, I fail to understand why we have to assign the same
 198 associativity to operators with the same precedence.  For instance,
 199 why can't I decide that the precedence of * and / is the same, but the
 200 latter is nonassoc?
 201
 202 If there is really no profound motivation, we should find a new syntax
 203 to allow specifying this.
 204
 205 ** RR conflicts
 206 See if we can use precedence between rules to solve RR conflicts.  See
 207 what POSIX says.
 208
 209
 210 * $undefined
 211 From Hans:
 212 - If the Bison generated parser experiences an undefined number in the
 213 character range, that character is written out in diagnostic messages, an
 214 addition to the $undefined value.
 215
 216 Suggest: Change the name $undefined to undefined; looks better in outputs.
 217
 218
 219 * Default Action
 220 From Hans:
 221 - For use with my C++ parser, I transported the "switch (yyn)" statement
 222 that Bison writes to the bison.simple skeleton file. This way, I can remove
 223 the current default rule $$ = $1 implementation, which causes a double
 224 assignment to $$ which may not be OK under C++, replacing it with a
 225 "default:" part within the switch statement.
 226
 227 Note that the default rule $$ = $1, when typed, is perfectly OK under C,
 228 but in the C++ implementation I made, this rule is different from
 229 $<type_name>$ = $<type_name>1. I therefore think that one should implement
 230 a Bison option where every typed default rule is explicitly written out
 231 (same typed ruled can of course be grouped together).
 232
 233 Note: Robert Anisko handles this.  He knows how to do it.
 234
 235
 236 * Warnings
 237 It would be nice to have warning support.  See how Autoconf handles
 238 them, it is fairly well described there.  It would be very nice to
 239 implement this in such a way that other programs could use
 240 lib/warnings.[ch].
 241
 242 Don't work on this without first announcing you do, as I already have
 243 thought about it, and know many of the components that can be used to
 244 implement it.
 245
 246
 247 * Pre and post actions.
 248 From: Florian Krohm <florian@edamail.fishkill.ibm.com>
 249 Subject: YYACT_EPILOGUE
 250 To: bug-bison@gnu.org
 251 X-Sent: 1 week, 4 days, 14 hours, 38 minutes, 11 seconds ago
 252
 253 The other day I had the need for explicitly building the parse tree. I
 254 used %locations for that and defined YYLLOC_DEFAULT to call a function
 255 that returns the tree node for the production. Easy. But I also needed
 256 to assign the S-attribute to the tree node. That cannot be done in
 257 YYLLOC_DEFAULT, because it is invoked before the action is executed.
 258 The way I solved this was to define a macro YYACT_EPILOGUE that would
 259 be invoked after the action. For reasons of symmetry I also added
 260 YYACT_PROLOGUE. Although I had no use for that I can envision how it
 261 might come in handy for debugging purposes.
 262 All is needed is to add
 263
 264 #if YYLSP_NEEDED
 265     YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen));
 266 #else
 267     YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen);
 268 #endif
 269
 270 at the proper place to bison.simple. Ditto for YYACT_PROLOGUE.
 271
 272 I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE
 273 to bison. If you're interested, I'll work on a patch.
 274
 275 * Move to Graphviz
 276 Well, VCG seems really dead.  Move to Graphviz instead.  Also, equip
 277 the parser with a means to create the (visual) parse tree.
 278
 279 -----
 280
 281 Copyright (C) 2001, 2002 Free Software Foundation, Inc.
 282
 283 This file is part of GNU Bison.
 284
 285 GNU Bison is free software; you can redistribute it and/or modify
 286 it under the terms of the GNU General Public License as published by
 287 the Free Software Foundation; either version 2, or (at your option)
 288 any later version.
 289
 290 GNU Bison is distributed in the hope that it will be useful,
 291 but WITHOUT ANY WARRANTY; without even the implied warranty of
 292 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 293 GNU General Public License for more details.
 294
 295 You should have received a copy of the GNU General Public License
 296 along with Bison; see the file COPYING.  If not, write to
 297 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 298 Boston, MA 02111-1307, USA.