X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/b4cbf822eba2133e123d165603bc5542c5662b33..6c35d22c399d53cc4ce2b0f594a3033ede3ae117:/TODO diff --git a/TODO b/TODO index 27d2c084..d3725032 100644 --- a/TODO +++ b/TODO @@ -1,49 +1,46 @@ -*- outline -*- +* URGENT: Documenting C++ output +Write a first documentation for C++ output. -* URGENT: Prologue -The %union is declared after the user C declarations. It can be -a problem if YYSTYPE is declared after the user part. +* value_components_used +Was defined but not used: where was it coming from? It can't be to +check if %union is used, since the user is free to $n on her +union, doesn't she? -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" - ... - %} +* 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... - %union { - unsigned long int num; - enum operator op; - struct expression *exp; - } +* documentation +Explain $axiom (and maybe change its name: BTYacc names it `goal', +byacc `$accept' probably based on AT&T Yacc, Meta `Start'...). +Complete the glossary (item, axiom, ?). - %{ - ... - static int yylex PARAMS ((YYSTYPE *lval, const char **pexp)); - ... - %} +* Error messages +Some are really funky. For instance -Where the first part defines struct expression, the second uses it to -define YYSTYPE, and the last uses YYSTYPE. Only this order is valid. + type clash (`%s' `%s') on default action -Note that we have the same problem with GCC. +is really weird. Revisit them all. -I suggest splitting the prologue into pre-prologue and post-prologue. -The reason is that: +* Report documentation +Extend with error. The hard part will probably be finding the right +rule so that a single state does not exhibit to many yet undocumented +``features''. Maybe an empty action ought to be presented too. Shall +we try to make a single grammar with all these features, or should we +have several very small grammars? -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) +* Documentation +Some history of Bison and some bibliography would be most welcome. +Are there any Texinfo standards for bibliography? -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. +* 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: @@ -60,30 +57,10 @@ When implementing multiple-%union support, bare the following in mind: 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 ]. +* --report=conflict-path +Provide better assistance for understanding the conflicts by providing +a sample text exhibiting the (LALR) ambiguity. See the paper from +DeRemer and Penello: they already provide the algorithm. * Coding system independence Paul notes: @@ -98,36 +75,6 @@ Paul notes: 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 - ... - -> 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: @@ -211,7 +158,10 @@ into exp: exp '+' exp | exp '&' exp; when there are no actions. This can significantly speed up some -grammars. +grammars. I can't find the papers. In particular the book `LR +parsing: Theory and Practice' is impossible to find, but according to +`Parsing Techniques: a Practical Guide', it includes information about +this issue. Does anybody have it? * Stupid error messages An example shows it easily: @@ -237,11 +187,6 @@ 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. @@ -263,7 +208,6 @@ 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. @@ -352,9 +296,6 @@ should recognize these, and preserve them. See if we can integrate backtracking in Bison. Contact the BTYacc maintainers. -* Automaton report -Display more clearly the lookaheads for each item. - * RR conflicts See if we can use precedence between rules to solve RR conflicts. See what POSIX says. @@ -364,55 +305,16 @@ It is unfortunate that there is a total order for precedence. It makes it impossible to have modular precedence information. We should move to partial orders. +This will be possible with a Bison parser for the grammar, as it will +make it much easier to extend the grammar. + * 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.) +Rewrite the reader in Flex/Bison. There will be delicate parts, in +particular, expect the scanner to be hard to write. Many interesting +features cannot be implemented without such a new reader. +I'm on it! I already have a proto that parses (but the actions are +not fully written yet). -- Akim * $undefined From Hans: @@ -436,6 +338,18 @@ $$ = $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). +Note: Robert Anisko handles this. He knows how to do it. + +* Warnings +It would be nice to have warning support. See how Autoconf handles +them, it is fairly well described there. It would be very nice to +implement this in such a way that other programs could use +lib/warnings.[ch]. + +Don't work on this without first announcing you do, as I already have +thought about it, and know many of the components that can be used to +implement it. + * Pre and post actions. From: Florian Krohm Subject: YYACT_EPILOGUE @@ -464,6 +378,10 @@ 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. +* Move to Graphviz +Well, VCG seems really dead. Move to Graphviz instead. Also, equip +the parser with a means to create the (visual) parse tree. + ----- Copyright (C) 2001, 2002 Free Software Foundation, Inc.