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

[bison.git] / TODO

diff --git a/TODO b/TODO
index c056bbbb663c9c1f0226eac3d7b8f497e90ec7a4..49775d1857d1a2757688a4254c2357f994d1c1e9 100644 (file)
--- a/TODO
+++ b/TODO
@@ -1,149 +1,112 @@
 -*- outline -*-
 
 -*- 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.
+* URGENT: Documenting C++ output
+Write a first documentation for C++ output.

 
 

-- The #line must now appear *inside* the definition of yystype.
-  Something like

 
 

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

 
 

-* Experimental report features
-Decide whether they should be enabled, or optional.  For instance, on:

 
 

-       input:
-         exp
-       | input exp
-       ;
+* Error messages
+Some are really funky.  For instance

 
 

-       exp:
-         token1 "1"
-       | token2 "2"
-       | token3 "3"
-       ;
+       type clash (`%s' `%s') on default action

 
 

-       token1: token;
-       token2: token;
-       token3: token;
+is really weird.  Revisit them all.

 
 

-the traditional Bison reports:

 
 

-       state 0
+* 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.

 
 

-           $axiom  ->  . input $   (rule 0)

 
 

-           token       shift, and go to state 1
+* 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?

 
 

-           input       go to state 2
-           exp         go to state 3
-           token1      go to state 4
-           token2      go to state 5
-           token3      go to state 6

 
 

-       state 1
+* Report

 
 

-           token1  ->  token .   (rule 6)
-           token2  ->  token .   (rule 7)
-           token3  ->  token .   (rule 8)
+**  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.

 
 

-           "2"         reduce using rule 7 (token2)
-           "3"         reduce using rule 8 (token3)
-           $default    reduce using rule 6 (token1)
+** Disabled Reductions
+See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
+what we want to do.

 
 

-while with --trace, i.e., when enabling both the display of non-core
-item sets and the display of lookaheads, Bison now displays:
+** 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?

 
 

-       state 0
+** --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.

 
 

-           $axiom  ->  . input $   (rule 0)
-           input  ->  . exp   (rule 1)
-           input  ->  . input exp   (rule 2)
-           exp  ->  . token1 "1"   (rule 3)
-           exp  ->  . token2 "2"   (rule 4)
-           exp  ->  . token3 "3"   (rule 5)
-           token1  ->  . token   (rule 6)
-           token2  ->  . token   (rule 7)
-           token3  ->  . token   (rule 8)

 
 

-           token       shift, and go to state 1
+* Extentions

 
 

-           input       go to state 2
-           exp         go to state 3
-           token1      go to state 4
-           token2      go to state 5
-           token3      go to state 6
+** 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...

 
 

-       state 1
+** 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.

 
 

-           token1  ->  token .  ["1"]   (rule 6)
-           token2  ->  token .  ["2"]   (rule 7)
-           token3  ->  token .  ["3"]   (rule 8)
+When implementing multiple-%union support, bare the following in mind:

 
 

-           "2"         reduce using rule 7 (token2)
-           "3"         reduce using rule 8 (token3)
-           $default    reduce using rule 6 (token1)
+- when --yacc, this must be flagged as an error.  Don't make it fatal
+  though.

 
 

-so decide whether this should be an option, or always enabled.  I'm in
-favor of making it the default, but maybe we should tune the output to
-distinguish core item sets from non core:
+- The #line must now appear *inside* the definition of yystype.
+  Something like

 
 

-       state 0
-           Core:
-           $axiom  ->  . input $   (rule 0)
+       {
+       #line 12 "foo.y"
+         int ival;
+       #line 23 "foo.y"
+         char *sval;
+       }

 
 

-           Derived:
-           input  ->  . exp   (rule 1)
-           input  ->  . input exp   (rule 2)
-           exp  ->  . token1 "1"   (rule 3)
-           exp  ->  . token2 "2"   (rule 4)
-           exp  ->  . token3 "3"   (rule 5)
-           token1  ->  . token   (rule 6)
-           token2  ->  . token   (rule 7)
-           token3  ->  . token   (rule 8)
+* Unit rules
+Maybe we could expand unit rules, i.e., transform

 
 

-           token       shift, and go to state 1
+       exp: arith | bool;
+       arith: exp '+' exp;
+       bool: exp '&' exp;

 
 

-           input       go to state 2
-           exp         go to state 3
-           token1      go to state 4
-           token2      go to state 5
-           token3      go to state 6
+into

 
 

+       exp: exp '+' exp | exp '&' exp;

 
 

-> So, it seems clear that it has to be an additional option :)
+when there are no actions.  This can significantly speed up some
+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?

 
 

-Paul:

 
 

-       There will be further such options in the future, so I'd make
-       them all operands of the --report option.  E.g., you could do
-       something like this:

 
 

-       --report=state --report=lookahead --report=itemset
-       --report=conflict-path
+* Documentation

 
 

-       where "--verbose" is equivalent to "--report=state", and where
-       "--report=conflict-path" reports each path to a conflict
-       state.
+** History/Bibliography
+Some history of Bison and some bibliography would be most welcome.
+Are there any Texinfo standards for bibliography?

 
 

-       (As a minor point, I prefer avoiding plurals in option names.
-       It's partly for brevity, and partly to avoid wearing out the
-       's' keys in our keyboards.  :-)

 
 

-To implement this, see in the Fileutils the latest versions of
-argmatch and so forth.

 
 
 * Coding system independence
 
 
 * Coding system independence


@@ -159,133 +122,7 @@ Paul notes:
        PDP-10 ports :-) but they should probably be documented
        somewhere.
 
        PDP-10 ports :-) but they should probably be documented
        somewhere.
 

-* 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
-
-       exp: arith | bool;
-       arith: exp '+' exp;
-       bool: exp '&' exp;
-
-into
-
-       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.

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


@@ -321,59 +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.


@@ -382,39 +166,46 @@ 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.
+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.
 
 
 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 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.
-
-* 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.)
+** 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
 From Hans:
 
 * $undefined
 From Hans:


@@ -424,6 +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


@@ -440,8 +232,6 @@ a Bison option where every typed default rule is explicitly written out
 
 Note: Robert Anisko handles this.  He knows how to do it.
 
 
 Note: Robert Anisko handles this.  He knows how to do it.
 

-* Documenting C++ output
-Write a first documentation for C++ output.

 
 * Warnings
 It would be nice to have warning support.  See how Autoconf handles
 
 * Warnings
 It would be nice to have warning support.  See how Autoconf handles


@@ -453,6 +243,7 @@ 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.
 
 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


@@ -481,23 +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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+GNU Bison is distributed in the hope that it will be useful,

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