X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/20c37f213a14c112251907734402cbf80f44d780..b98ec53ee42edc8c709505472faca84d1cd4b4c3:/TODO diff --git a/TODO b/TODO index c87808a3..43405335 100644 --- a/TODO +++ b/TODO @@ -1,5 +1,90 @@ -*- outline -*- + +* URGENT: 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. + +Note that we have the same problem with GCC. + +I suggest splitting the prologue into pre-prologue and post-prologue. +The reason is that: + +1. we keep language independance as it is the skeleton that joins the +two prologues (there is no need for the engine to encode union yystype +and to output it inside the prologue, which breaks the language +independance of the generator) + +2. that makes it possible to have several %union in input. 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: @@ -33,16 +118,6 @@ Paul suggests: #define BAR 257 ... -> I'm in favor of -> -> %token FOO 256 -> %token BAR 257 -> -> and Bison moves error into 258. - -Yes, I think that's a valid extension too, if the user doesn't define -the token number for error. - * Output directory Akim: @@ -171,40 +246,6 @@ 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. - -Note that we have the same problem with GCC. - * --graph Show reductions. [] @@ -363,6 +404,56 @@ 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.