X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/aef1ffd56f6a9cd1ffcaa9f4c5f496f4f74ea82a..84614e137327c1ed6eba23c9b89bd6e587de0d45:/TODO diff --git a/TODO b/TODO index 0e385ebc..7514df80 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,155 @@ -*- outline -*- +* Several %unions +I think this is a pleasant (but useless currently) feature, but in the +future, I want a means to %include other bits of grammars, and _then_ +it will be important for the various bits to define their needs in +%union. + +When implementing multiple-%union support, bare the following in mind: + +- when --yacc, this must be flagged as an error. Don't make it fatal + though. + +- The #line must now appear *inside* the definition of yystype. + Something like + + { + #line 12 "foo.y" + int ival; + #line 23 "foo.y" + char *sval; + } + +* Language independent actions + +Currently bison, the generator, transforms $1, $$ and so forth into +direct C code, manipulating the stacks. This is problematic, because +(i) it means that if we want more languages, we need to update the +generator, and (ii), it forces names everywhere (e.g., the C++ +skeleton would be happy to use other naming schemes, and actually, +even other accessing schemes). + +Therefore we want + +1. the generator to replace $1, etc. by M4 macro invocations + (b4_dollar(1), b4_at(3), b4_dollar_dollar) etc. + +2. the skeletons to define these macros. + +But currently the actions are double-quoted, to protect them from M4 +evaluation. So we need to: + +3. stop quoting them + +4. change the [ and ] in the actions into @<:@ and @:>@ + +5. extend the postprocessor to maps these back onto [ and ]. + +* 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. + +* Using enums instead of int for tokens. +Paul suggests: + + #ifndef YYTOKENTYPE + # if defined (__STDC__) || defined (__cplusplus) + /* Put the tokens into the symbol table, so that GDB and other debuggers + know about them. */ + enum yytokentype { + FOO = 256, + BAR, + ... + }; + /* POSIX requires `int' for tokens in interfaces. */ + # define YYTOKENTYPE int + # endif + #endif + #define FOO 256 + #define BAR 257 + ... + +* Output directory +Akim: + +| I consider this to be a bug in bison: +| +| /tmp % mkdir src +| /tmp % cp ~/src/bison/tests/calc.y src +| /tmp % mkdir build && cd build +| /tmp/build % bison ../src/calc.y +| /tmp/build % cd .. +| /tmp % ls -l build src +| build: +| total 0 +| +| src: +| total 32 +| -rw-r--r-- 1 akim lrde 27553 oct 2 16:31 calc.tab.c +| -rw-r--r-- 1 akim lrde 3335 oct 2 16:31 calc.y +| +| +| Would it be safe to change this behavior to something more reasonable? +| Do you think some people depend upon this? + +Jim: + +Is it that behavior documented? +If so, then it's probably not reasonable to change it. +I've Cc'd the automake list, because some of automake's +rules use bison through $(YACC) -- though I'll bet they +all use it in yacc-compatible mode. + +Pavel: + +Hello, Jim and others! + +> Is it that behavior documented? +> If so, then it's probably not reasonable to change it. +> I've Cc'd the automake list, because some of automake's +> rules use bison through $(YACC) -- though I'll bet they +> all use it in yacc-compatible mode. + +Yes, Automake currently used bison in Automake-compatible mode, but it +would be fair for Automake to switch to the native mode as long as the +processed files are distributed and "missing" emulates bison. + +In any case, the makefiles should specify the output file explicitly +instead of relying on weird defaults. + +> | src: +> | total 32 +> | -rw-r--r-- 1 akim lrde 27553 oct 2 16:31 calc.tab.c +> | -rw-r--r-- 1 akim lrde 3335 oct 2 16:31 calc.y + +This is not _that_ ugly as it seems - with Automake you want to put +sources where they belong - to the source directory. + +> | This is not _that_ ugly as it seems - with Automake you want to put +> | sources where they belong - to the source directory. +> +> The difference source/build you are referring to is based on Automake +> concepts. They have no sense at all for tools such as bison or gcc +> etc. They have input and output. I do not want them to try to grasp +> source/build. I want them to behave uniformly: output *here*. + +I realize that. + +It's unfortunate that the native mode of Bison behaves in a less uniform +way than the yacc mode. I agree with your point. Bison maintainters may +want to fix it along with the documentation. + + * Unit rules Maybe we could expand unit rules, i.e., transform @@ -38,6 +188,11 @@ src/bison/tests % cd ./testsuite.dir/51 tests/testsuite.dir/51 % echo "()" | ./calc 1.2-1.3: parse error, unexpected ')', expecting error or "number" or '-' or '(' +* yyerror, yyprint interface +It should be improved, in particular when using Bison features such as +locations, and YYPARSE_PARAMS. For the time being, it is recommended +to #define yyerror and yyprint to steal internal variables... + * read_pipe.c This is not portable to DOS for instance. Implement a more portable scheme. Sources of inspiration include GNU diff, and Free Recode. @@ -52,38 +207,6 @@ critical for user data: when aborting a parsing, when handling the error token etc., we often throw away yylval without giving a chance of cleaning it up to the user. -* NEWS -Sort from 1.31 NEWS. - -* Prologue -The %union is declared after the user C declarations. It can be -a problem if YYSTYPE is declared after the user part. [] - -Actually, the real problem seems that the %union ought to be output -where it was defined. For instance, in gettext/intl/plural.y, we -have: - - %{ - ... - #include "gettextP.h" - ... - %} - - %union { - unsigned long int num; - enum operator op; - struct expression *exp; - } - - %{ - ... - static int yylex PARAMS ((YYSTYPE *lval, const char **pexp)); - ... - %} - -Where the first part defines struct expression, the second uses it to -define YYSTYPE, and the last uses YYSTYPE. Only this order is valid. - * --graph Show reductions. [] @@ -91,7 +214,6 @@ Show reductions. [] ** %no-lines [ok] ** %no-parser [] ** %pure-parser [] -** %semantic-parser [] ** %token-table [] ** Options which could use parse_dquoted_param (). Maybe transfered in lex.c. @@ -194,3 +316,121 @@ move to partial orders. * Parsing grammars Rewrite the reader in Bison. + +* Problems with aliases +From: "Baum, Nathan I" +Subject: Token Alias Bug +To: "'bug-bison@gnu.org'" + +I've noticed a bug in bison. Sadly, our eternally wise sysadmins won't let +us use CVS, so I can't find out if it's been fixed already... + +Basically, I made a program (in flex) that went through a .y file looking +for "..."-tokens, and then outputed a %token +line for it. For single-character ""-tokens, I reasoned, I could just use +[%token 'A' "A"]. However, this causes Bison to output a [#define 'A' 65], +which cppp chokes on, not unreasonably. (And even if cppp didn't choke, I +obviously wouldn't want (char)'A' to be replaced with (int)65 throughout my +code. + +Bison normally forgoes outputing a #define for a character token. However, +it always outputs an aliased token -- even if the token is an alias for a +character token. We don't want that. The problem is in /output.c/, as I +recall. When it outputs the token definitions, it checks for a character +token, and then checks for an alias token. If the character token check is +placed after the alias check, then it works correctly. + +Alias tokens seem to be something of a kludge. What about an [%alias "..."] +command... + + %alias T_IF "IF" + +Hmm. I can't help thinking... What about a --generate-lex option that +creates an .l file for the alias tokens used... (Or an option to make a +gperf file, etc...) + +* Presentation of the report file +From: "Baum, Nathan I" +Subject: Token Alias Bug +To: "'bug-bison@gnu.org'" + +I've also noticed something, that whilst not *wrong*, is inconvienient: I +use the verbose mode to help find the causes of unresolved shift/reduce +conflicts. However, this mode insists on starting the .output file with a +list of *resolved* conflicts, something I find quite useless. Might it be +possible to define a -v mode, and a -vv mode -- Where the -vv mode shows +everything, but the -v mode only tells you what you need for examining +conflicts? (Or, perhaps, a "*** This state has N conflicts ***" marker above +each state with conflicts.) + + +* $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. + +----- + +Copyright (C) 2001, 2002 Free Software Foundation, Inc. + +This file is part of GNU Autoconf. + +GNU Autoconf 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 2, or (at your option) +any later version. + +GNU Autoconf 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. 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