In verbose parse error message, don't report `error' as an

[bison.git] / TODO

diff --git a/TODO b/TODO
index e94652cd35f24d50231813ebc54bf0ca3624d22d..49775d1857d1a2757688a4254c2357f994d1c1e9 100644 (file)
--- a/TODO
+++ b/TODO
@@ -1,6 +1,66 @@
 -*- outline -*-
 
 -*- outline -*-
 

-* Several %unions
+* URGENT: Documenting C++ output
+Write a first documentation for C++ output.
+
+
+* Documentation
+Before releasing, make sure the documentation refers to the current
+`output' format.
+
+
+* Error messages
+Some are really funky.  For instance
+
+       type clash (`%s' `%s') on default action
+
+is really weird.  Revisit them all.
+
+
+* 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.
+
+
+* 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 $<foo>n on her
+union, doesn't she?
+
+
+* Report
+
+**  GLR
+How would Paul like to display the conflicted actions?  In particular,
+what when two reductions are possible on a given lookahead, 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.
+
+
+* Extentions
+
+** yyerror, yysymprint 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...
+
+** 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
 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


@@ -21,110 +81,6 @@ When implementing multiple-%union support, bare the following in mind:
          char *sval;
        }
 
          char *sval;
        }
 

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


@@ -137,50 +93,36 @@ 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...
+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?

 
 

-* 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.
+* Documentation
+
+** History/Bibliography
+Some history of Bison and some bibliography would be most welcome.
+Are there any Texinfo standards for bibliography?
+
+
+
+
+* 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.
+
+

 
 * --graph
 Show reductions.       []
 
 * --graph
 Show reductions.       []


@@ -216,59 +158,6 @@ skeleton muscles.  []
 ** tests/pure-parser.at        []
 New tests.
 
 ** 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.
 * input synclines
 Some users create their foo.y files, and equip them with #line.  Bison
 should recognize these, and preserve them.


@@ -277,66 +166,45 @@ should recognize these, and preserve them.
 See if we can integrate backtracking in Bison.  Contact the BTYacc
 maintainers.
 
 See if we can integrate backtracking in Bison.  Contact the BTYacc
 maintainers.
 

-* Automaton report
-Display more clearly the lookaheads for each item.
+** 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 adjustements 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++.
+
+** Improve the skeletons
+Have them support yysymprint, yydestruct and so forth.

 
 

-* 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).
+
+This will be possible with a Bison parser for the grammar, as it will
+make it much easier to extend the grammar.
+
+** Correlation b/w precedence and associativity
+Also, I fail to understand why we have to assign the same
+associativity to operators with the same precedence.  For instance,
+why can't I decide that the precedence of * and / is the same, but the
+latter is nonassoc?
+
+If there is really no profound motivation, we should find a new syntax
+to allow specifying this.
+
+** RR conflicts
+See if we can use precedence between rules to solve RR conflicts.  See
+what POSIX says.

 
 
 * $undefined
 
 
 * $undefined


@@ -347,6 +215,7 @@ 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


@@ -361,6 +230,20 @@ $<type_name>$ = $<type_name>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).
 
 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 <florian@edamail.fishkill.ibm.com>
 Subject: YYACT_EPILOGUE
 * Pre and post actions.
 From: Florian Krohm <florian@edamail.fishkill.ibm.com>
 Subject: YYACT_EPILOGUE


@@ -389,23 +272,27 @@ 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.
 

+* 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.
+

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