-*- outline -*-
+* Short term
+** Use syntax_error from the scanner?
+This would provide a means to raise syntax error from function called
+from the scanner. Actually, there is no good solution to report a
+lexical error in general. Usually they are kept at the scanner level
+only, ignoring the guilty token. But that might not be the best bet,
+since we don't benefit from the syntactic error recovery.
+
+We still have the possibility to return an invalid token number, which
+does the trick. But then the error message from the parser is poor
+(something like "unexpected $undefined"). Since the scanner probably
+already reported the error, we should directly enter error-recovery,
+without reporting the error message (i.e., YYERROR's semantics).
+
+Back to lalr1.cc (whose name is now quite unfortunate, since it also
+covers lr and ielr), if we support exceptions from yylex, should we
+propose a lexical_error in addition to syntax_error? Should they have
+a common root, say parse_error? Should syntax_error be renamed
+syntactic_error for consistency with lexical_error?
+
+** Variable names.
+What should we name `variant' and `lex_symbol'?
+
+** Use b4_symbol in all the skeleton
+Then remove the older system, including the tables generated by
+output.c
+
+** Update the documentation on gnu.org
+
+** Get rid of fake #lines [Bison: ...]
+Possibly as simple as checking whether the column number is nonnegative.
+
+I have seen messages like the following from GCC.
+
+<built-in>:0: fatal error: opening dependency file .deps/libltdl/argz.Tpo: No such file or directory
+
+
+** Discuss about %printer/%destroy in the case of C++.
+It would be very nice to provide the symbol classes with an operator<<
+and a destructor. Unfortunately the syntax we have chosen for
+%destroy and %printer make them hard to reuse. For instance, the user
+is invited to write something like
+
+ %printer { debug_stream() << $$; } <my_type>;
+
+which is hard to reuse elsewhere since it wants to use
+"debug_stream()" to find the stream to use. The same applies to
+%destroy: we told the user she could use the members of the Parser
+class in the printers/destructors, which is not good for an operator<<
+since it is no longer bound to a particular parser, it's just a
+(standalone symbol).
+
+** Rename LR0.cc
+as lr0.cc, why upper case?
+
+** bench several bisons.
+Enhance bench.pl with %b to run different bisons.
+
+** Use b4_symbol everywhere.
+Move its definition in the more standard places and deploy it in other
+skeletons.
+
* Various
+** YYPRINT
+glr.c inherits its symbol_print function from c.m4, which supports
+YYPRINT. But to use YYPRINT yytoknum is needed, which not defined by
+glr.c.
+
+Anyway, IMHO YYPRINT is obsolete and should be restricted to yacc.c.
+
** 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?
+Also, why don't we output the token name of the error token in the
+output? It is explicitly skipped:
-** 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)
+ /* Skip error token and tokens without identifier. */
+ if (sym != errtoken && id)
+
+Of course there are issues with name spaces, but if we disable we have
+something which seems to be more simpler and more consistent instead
+of the special case YYERRCODE.
+
+ enum yytokentype {
+ error = 256,
+ // ...
+ };
+
+
+We could (should?) also treat the case of the undef_token, which is
+numbered 257 for yylex, and 2 internal. Both appear for instance in
+toknum:
+
+ const unsigned short int
+ parser::yytoken_number_[] =
{
- fprintf (stderr, "%s\n", msg);
- }
+ 0, 256, 257, 258, 259, 260, 261, 262, 263, 264,
+
+while here
- int
- main (void)
+ enum yytokentype {
+ TOK_EOF = 0,
+ TOK_EQ = 258,
+
+so both 256 and 257 are "mysterious".
+
+ const char*
+ const parser::yytname_[] =
{
- yydebug = !!getenv("YYDEBUG");
- return yyparse ();
- }
+ "\"end of command\"", "error", "$undefined", "\"=\"", "\"break\"",
+
+
+** YYFAIL
+It is seems to be *really* obsolete now, shall we remove it?
** yychar == yyempty_
The code in yyerrlab reads:
if (yychar <= YYEOF)
- {
- /* Return failure if at end of input. */
- if (yychar == YYEOF)
- YYABORT;
- }
+ {
+ /* Return failure if at end of input. */
+ if (yychar == YYEOF)
+ YYABORT;
+ }
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
we do the same in yacc.c.
** yysyntax_error
-In lalr1.cc we invoke it with the translated lookahead (yytoken), and
-yacc.c uses yychar. I don't see why.
+The code bw glr.c and yacc.c is really alike, we can certainly factor
+some parts.
* Header guards
* Report
+** Figures
+Some statistics about the grammar and the parser would be useful,
+especially when asking the user to send some information about the
+grammars she is working on. We should probably also include some
+information about the variables (I'm not sure for instance we even
+specify what LR variant was used).
+
** 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
* 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; }
+ baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; }
we should be able to have:
* Unit rules
Maybe we could expand unit rules, i.e., transform
- exp: arith | bool;
- arith: exp '+' exp;
- bool: exp '&' exp;
+ exp: arith | bool;
+ arith: exp '+' exp;
+ bool: exp '&' exp;
into
- exp: exp '+' exp | exp '&' exp;
+ exp: exp '+' exp | exp '&' exp;
when there are no actions. This can significantly speed up some
grammars. I can't find the papers. In particular the book `LR
Some history of Bison and some bibliography would be most welcome.
Are there any Texinfo standards for bibliography?
-
+** %printer
+Wow, %printer is not documented. Clearly mark YYPRINT as obsolete.
* 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.
+ 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.
+ 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
Show reductions.
* Better graphics
Equip the parser with a means to create the (visual) parse tree.
+* Complaint submessage indentation.
+We already have an implementation that works fairly well for named
+reference messages, but it would be nice to use it consistently for all
+submessages from Bison. For example, the "previous definition"
+submessage or the list of correct values for a %define variable might
+look better with indentation.
+
+However, the current implementation makes the assumption that the
+location printed on the first line is not usually much shorter than the
+locations printed on the submessage lines that follow. That assumption
+may not hold true as often for some kinds of submessages especially if
+we ever support multiple grammar files.
+
+Here's a proposal for how a new implementation might look:
+
+ http://lists.gnu.org/archive/html/bison-patches/2009-09/msg00086.html
+
-----
-Copyright (C) 2001, 2002, 2003, 2004, 2006, 2008 Free Software Foundation,
-Inc.
+Copyright (C) 2001-2004, 2006, 2008-2012 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
projects / bison.git / blobdiff