-*- 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
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
* 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
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
* 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, 2008-2009 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