TODO: yyfmt.

[bison.git] / TODO

diff --git a/TODO b/TODO
index 567e5b7365af7698412091729c4e7844ce0aa56d..9dbd6b423e4cd88e45eab24c78175e22458c18f6 100644 (file)
--- a/TODO
+++ b/TODO
@@ -1,178 +1,203 @@
 -*- outline -*-
 
 -*- outline -*-
 

+* Various
+** YYERRCODE
+Defined to 256, but not used, not documented.  Probably the token
+number for the error token, which POSIX wants to be 256, but which
+Bison might renumber if the user used number 256.  Keep fix and doc?
+Throw away?
+
+** YYFAIL
+It is seems to be *really* obsolete now, shall we remove it?
+
+** YYBACKUP
+There is no test about it, no examples in the doc, and I'm not sure
+what it should look like.  For instance what follows crashes.
+
+  %error-verbose
+  %debug
+  %pure-parser
+  %code {
+  # include <stdio.h>
+  # include <stdlib.h>
+  # include <assert.h>
+
+    static void yyerror (const char *msg);
+    static int yylex (YYSTYPE *yylval);
+  }
+  %%
+  exp:
+    'a'   { printf ("a: %d\n", $1); }
+  | 'b'   { YYBACKUP('a', 123); }
+  ;
+  %%
+  static int
+  yylex (YYSTYPE *yylval)
+  {
+    static char const input[] = "b";
+    static size_t toknum;
+    assert (toknum < sizeof input);
+    *yylval = (toknum + 1) * 10;
+    return input[toknum++];
+  }
+
+  static void
+  yyerror (const char *msg)
+  {
+    fprintf (stderr, "%s\n", msg);
+  }
+
+  int
+  main (void)
+  {
+    yydebug = !!getenv("YYDEBUG");
+    return yyparse ();
+  }
+
+** yychar == yyempty_
+The code in yyerrlab reads:
+
+      if (yychar <= YYEOF)
+       {
+         /* Return failure if at end of input.  */
+         if (yychar == YYEOF)
+           YYABORT;
+       }

 
 

-* URGENT: Prologue
-The %union is declared after the user C declarations. It can be
-a problem if YYSTYPE is declared after the user part.
+There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF.
+But I can't produce the situation where yychar is YYEMPTY here, is it
+really possible?  The test suite does not exercise this case.

 
 

-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:
+This shows that it would be interesting to manage to install skeleton
+coverage analysis to the test suite.

 
 

-       %{
-       ...
-       #include "gettextP.h"
-       ...
-       %}
+** Table definitions
+It should be very easy to factor the definition of the various tables,
+including the separation bw declaration and definition.  See for
+instance b4_table_define in lalr1.cc.  This way, we could even factor
+C vs. C++ definitions.

 
 

-       %union {
-         unsigned long int num;
-         enum operator op;
-         struct expression *exp;
-       }
+* From lalr1.cc to yacc.c
+** Single stack
+Merging the three stacks in lalr1.cc simplified the code, prompted for
+other improvements and also made it faster (probably because memory
+management is performed once instead of three times).  I suggest that
+we do the same in yacc.c.

 
 

-       %{
-       ...
-       static int yylex PARAMS ((YYSTYPE *lval, const char **pexp));
-       ...
-       %}
+** yysyntax_error
+In lalr1.cc we invoke it with the translated lookahead (yytoken), and
+yacc.c uses yychar.  I don't see why.

 
 

-Where the first part defines struct expression, the second uses it to
-define YYSTYPE, and the last uses YYSTYPE.  Only this order is valid.
+** yysyntax_error
+The use of switch to select yyfmt in lalr1.cc seems simpler than
+what's done in yacc.c.

 
 

-Note that we have the same problem with GCC.
+* Header guards

 
 

-I suggest splitting the prologue into pre-prologue and post-prologue.
-The reason is that:
+From Franc,ois: should we keep the directory part in the CPP guard?

 
 

-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.
+* Yacc.c: CPP Macros

 
 

-When implementing multiple-%union support, bare the following in mind:
+Do some people use YYPURE, YYLSP_NEEDED like we do in the test suite?
+They should not: it is not documented.  But if they need to, let's
+find something clean (not like YYLSP_NEEDED...).

 
 

-- 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
+* Installation

 
 

-       {
-       #line 12 "foo.y"
-         int ival;
-       #line 23 "foo.y"
-         char *sval;
-       }
+* Documentation
+Before releasing, make sure the documentation ("Understanding your
+parser") refers to the current `output' format.

 
 

-* Coding system independence
-Paul notes:
+* Report

 
 

-       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.
+**  GLR
+How would Paul like to display the conflicted actions?  In particular,
+what when two reductions are possible on a given lookahead token, but one is
+part of $default.  Should we make the two reductions explicit, or just
+keep $default?  See the following point.
+
+** Disabled Reductions
+See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
+what we want to do.
+
+** Documentation
+Extend with error productions.  The hard part will probably be finding
+the right rule so that a single state does not exhibit too 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?
+
+** --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.
+
+** Statically check for potential ambiguities in GLR grammars.  See
+<http://www.i3s.unice.fr/~schmitz/papers.html#expamb> for an approach.
+
+
+* Extensions
+
+** Labeling the symbols
+Have a look at the Lemon parser generator: instead of $1, $2 etc. they
+can name the values.  This is much more pleasant.  For instance:
+
+       exp (res): exp (a) '+' exp (b) { $res = $a + $b; };
+
+I love this.  I have been bitten too often by the removal of the
+symbol, and forgetting to shift all the $n to $n-1.  If you are
+unlucky, it compiles...
+
+But instead of using $a etc., we can use regular variables.  And
+instead of using (), I propose to use `:' (again).  Paul suggests
+supporting `->' in addition to `:' to separate LHS and RHS. In other
+words:
+
+       r:exp -> a:exp '+' b:exp { r = a + b; };
+
+That requires an significant improvement of the grammar parser.  Using
+GLR would be nice.  It also requires that Bison know the type of the
+symbols (which will be useful for %include anyway).  So we have some
+time before...
+
+Note that there remains the problem of locations: `@r'?
+
+
+** $-1
+We should find a means to provide an access to values deep in the
+stack.  For instance, instead of
+
+       baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; }
+
+we should be able to have:
+
+  foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; }
+
+Or something like this.

 
 

-* 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:
-
-| 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.
+** %if and the like
+It should be possible to have %if/%else/%endif.  The implementation is
+not clear: should it be lexical or syntactic.  Vadim Maslow thinks it
+must be in the scanner: we must not parse what is in a switched off
+part of %if.  Akim Demaille thinks it should be in the parser, so as
+to avoid falling into another CPP mistake.

 
 

+** XML Output
+There are couple of available extensions of Bison targeting some XML
+output.  Some day we should consider including them.  One issue is
+that they seem to be quite orthogonal to the parsing technique, and
+seem to depend mostly on the possibility to have some code triggered
+for each reduction.  As a matter of fact, such hooks could also be
+used to generate the yydebug traces.  Some generic scheme probably
+exists in there.
+
+XML output for GNU Bison and gcc
+   http://www.cs.may.ie/~jpower/Research/bisonXML/
+
+XML output for GNU Bison
+   http://yaxx.sourceforge.net/

 
 * Unit rules
 Maybe we could expand unit rules, i.e., transform
 
 * Unit rules
 Maybe we could expand unit rules, i.e., transform


@@ -186,207 +211,82 @@ into
        exp: exp '+' exp | exp '&' exp;
 
 when there are no actions.  This can significantly speed up some
        exp: exp '+' exp | exp '&' exp;
 
 when there are no actions.  This can significantly speed up some

-grammars.
-
-* Stupid error messages
-An example shows it easily:
-
-src/bison/tests % ./testsuite -k calc,location,error-verbose -l
-GNU Bison 1.49a test suite test groups:
-
- NUM: FILENAME:LINE      TEST-GROUP-NAME
-      KEYWORDS
-
-  51: calc.at:440        Calculator --locations --yyerror-verbose
-  52: calc.at:442        Calculator --defines --locations --name-prefix=calc --verbose --yacc --yyerror-verbose
-  54: calc.at:445        Calculator --debug --defines --locations --name-prefix=calc --verbose --yacc --yyerror-verbose
-src/bison/tests % ./testsuite 51 -d
-## --------------------------- ##
-## GNU Bison 1.49a test suite. ##
-## --------------------------- ##
- 51: calc.at:440       ok
-## ---------------------------- ##
-## All 1 tests were successful. ##
-## ---------------------------- ##
-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.
-
-* Memory leaks in the generator
-A round of memory leak clean ups would be most welcome.  Dmalloc,
-Checker GCC, Electric Fence, or Valgrind: you chose your tool.
-
-* Memory leaks in the parser
-The same applies to the generated parsers.  In particular, this is
-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.
+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?
+
+
+
+* Documentation
+
+** History/Bibliography
+Some history of Bison and some bibliography would be most welcome.
+Are there any Texinfo standards for bibliography?
+
+
+
+* Java, Fortran, etc.
+
+
+* 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.
+
+       More importantly, Bison does not currently allow NUL bytes in
+       tokens, either via escapes (e.g., "x\0y") or via a NUL byte in
+       the source code.  This should get fixed.

 
 * --graph
 
 * --graph

-Show reductions.       []
+Show reductions.

 
 * Broken options ?
 
 * Broken options ?

-** %no-lines           [ok]
-** %no-parser          []
-** %pure-parser                []
-** %semantic-parser    []
-** %token-table                []
-** Options which could use parse_dquoted_param ().
-Maybe transfered in lex.c.
-*** %skeleton          [ok]
-*** %output            []
-*** %file-prefix       []
-*** %name-prefix       []
-
-** Skeleton strategy.  []
-Must we keep %no-parser?
-            %token-table?
-*** New skeletons.     []
-
-* src/print_graph.c
-Find the best graph parameters.        []
-
-* doc/bison.texinfo
-** Update
-informations about ERROR_VERBOSE.      []
-** Add explainations about
-skeleton muscles.      []
-%skeleton.             []
-
-* testsuite
-** tests/pure-parser.at        []
-New tests.
-
-* Debugging parsers
-
-From Greg McGary:
-
-akim demaille <akim.demaille@epita.fr> writes:
-
-> With great pleasure!  Nonetheless, things which are debatable
-> (or not, but just `big') should be discuss in `public': something
-> like help- or bug-bison@gnu.org is just fine.  Jesse and I are there,
-> but there is also Jim and some other people.
-
-I have no idea whether it qualifies as big or controversial, so I'll
-just summarize for you.  I proposed this change years ago and was
-surprised that it was met with utter indifference!
-
-This debug feature is for the programs/grammars one develops with
-bison, not for debugging bison itself.  I find that the YYDEBUG
-output comes in a very inconvenient format for my purposes.
-When debugging gcc, for instance, what I want is to see a trace of
-the sequence of reductions and the line#s for the semantic actions
-so I can follow what's happening.  Single-step in gdb doesn't cut it
-because to move from one semantic action to the next takes you through
-lots of internal machinery of the parser, which is uninteresting.
-
-The change I made was to the format of the debug output, so that it
-comes out in the format of C error messages, digestible by emacs
-compile mode, like so:
-
-grammar.y:1234: foo: bar(0x123456) baz(0x345678)
-
-where "foo: bar baz" is the reduction rule, whose semantic action
-appears on line 1234 of the bison grammar file grammar.y.  The hex
-numbers on the rhs tokens are the parse-stack values associated with
-those tokens.  Of course, yytype might be something totally
-incompatible with that representation, but for the most part, yytype
-values are single words (scalars or pointers).  In the case of gcc,
-they're most often pointers to tree nodes.  Come to think of it, the
-right thing to do is to make the printing of stack values be
-user-definable.  It would also be useful to include the filename &
-line# of the file being parsed, but the main filename & line# should
-continue to be that of grammar.y
-
-Anyway, this feature has saved my life on numerous occasions.  The way
-I customarily use it is to first run bison with the traces on, isolate
-the sequence of reductions that interests me, put those traces in a
-buffer and force it into compile-mode, then visit each of those lines
-in the grammar and set breakpoints with C-x SPACE.  Then, I can run
-again under the control of gdb and stop at each semantic action.
-With the hex addresses of tree nodes, I can inspect the values
-associated with any rhs token.
-
-You like?
-
-* input synclines
-Some users create their foo.y files, and equip them with #line.  Bison
-should recognize these, and preserve them.
+** %token-table
+** Skeleton strategy
+Must we keep %token-table?

 
 * BTYacc
 
 * BTYacc

-See if we can integrate backtracking in Bison.  Contact the BTYacc
-maintainers.
+See if we can integrate backtracking in Bison.  Charles-Henri de
+Boysson <de-boy_c@epita.fr> has been working on this, but never gave
+the results.

 
 

-* Automaton report
-Display more clearly the lookaheads for each item.
+Vadim Maslow, the maintainer of BTYacc was once contacted.  Adjusting
+the Bison grammar parser will be needed to support some extra BTYacc
+features.  This is less urgent.
+
+** Keeping the conflicted actions
+First, analyze the differences between byacc and btyacc (I'm referring
+to the executables).  Find where the conflicts are preserved.
+
+** Compare with the GLR tables
+See how isomorphic the way BTYacc and the way the GLR adjustments in
+Bison are compatible.  *As much as possible* one should try to use the
+same implementation in the Bison executables.  I insist: it should be
+very feasible to use the very same conflict tables.
+
+** Adjust the skeletons
+Import the skeletons for C and C++.

 
 

-* RR conflicts
-See if we can use precedence between rules to solve RR conflicts.  See
-what POSIX says.

 
 * Precedence
 
 * Precedence

+
+** Partial order

 It is unfortunate that there is a total order for precedence.  It
 makes it impossible to have modular precedence information.  We should
 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.
-
-* Parsing grammars
-Rewrite the reader in Bison.
-
-* Problems with aliases
-From: "Baum, Nathan I" <s0009525@chelt.ac.uk>
-Subject: Token Alias Bug
-To: "'bug-bison@gnu.org'" <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" <s0009525@chelt.ac.uk>
-Subject: Token Alias Bug
-To: "'bug-bison@gnu.org'" <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.)
+move to partial orders (sounds like series/parallel orders to me).
+
+** RR conflicts
+See if we can use precedence between rules to solve RR conflicts.  See
+what POSIX says.

 
 
 * $undefined
 
 
 * $undefined


@@ -397,6 +297,7 @@ addition to the $undefined value.
 
 Suggest: Change the name $undefined to undefined; looks better in outputs.
 
 
 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
 * Default Action
 From Hans:
 - For use with my C++ parser, I transported the "switch (yyn)" statement


@@ -439,23 +340,25 @@ 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.
 
 I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE
 to bison. If you're interested, I'll work on a patch.
 

+* Better graphics
+Equip the parser with a means to create the (visual) parse tree.
+

 -----
 
 -----
 

-Copyright (C) 2001, 2002 Free Software Foundation, Inc.
+Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008 Free Software Foundation,
+Inc.

 
 

-This file is part of GNU Autoconf.
+This file is part of Bison, the GNU Compiler Compiler.

 
 

-GNU Autoconf is free software; you can redistribute it and/or modify
+This program is free software: you can redistribute it and/or modify

 it under the terms of the GNU General Public License as published by
 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.
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.

 
 

-GNU Autoconf is distributed in the hope that it will be useful,
+This program 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.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License

-along with autoconf; see the file COPYING.  If not, write to
-the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA.
+along with this program.  If not, see <http://www.gnu.org/licenses/>.