Re: improving yysyntax_error()

[Hans Aberg]

It happened on 21 Jun 2007, at 22:02, that Christian Schoenebeck wrote:

> Es geschah am Thursday, 21. June 2007 20:18 als Hans Aberg schrieb:
> > How should %atomic be implemented?
>
> How it "should" be implemented is the wrong question, or at least  
> addressed to
> the wrong person, since I'm not familiar enough with the bison  
> implementation
> yet. That was actually my main reason to write to this list, to  
> probably get
> suggestions how this could fit into the current implementation of  
> bison.

So until somebody figure that out, it won't happen.

> > > The rest
> > > would be needed for implementing UTF-8 support.
> >
> > No, as sequences of bytes can be put directly into the rules.
>
> Either we have a misapprehension here, or this is exactly what I  
> did in my
> example, so I don't get the point.

As I wrote in my reply, one can already have token character  
sequences 'c_1'...'c_k' in the rules. If 'c_1...c_k' is interpreted  
as 'c_1'...'c_k', then if the grammar file is written in UTF-8, the  
parser will identify the UTF-8 multibyte sequence. So if the lexer  
feeds that to the parser, one will get an identification. But the  
error messages will currently only write out the leading byte.

> > > Another future
> > > application would be integrated type completion support within the
> > > bison
> > > skeleton parser.
> >
> > I cannot parse this. Please elaborate.
>
> With "intergrated type completion support" I mean a convenient way  
> for parser
> developers (or actually interpreter developers) to let the user  
> "complete"
> the current input upon the current parser state, in case there is  
> only one
> possible shift transition, that is for highly redundant languages.

This has been discussed here. One really need LR(1) for that, because  
LALR(1) compacts the states in way that the error tokens may not  
appear until some reductions have been performed (And so causing the  
same problem if one wants to find the completion tokens directly from  
the states).

LR(1) is being implemented now, but I do not know if it is the  
version that does not do this type of compaction.

  Hans Aberg