Re: [PATCH] todo: short term

[Akim Demaille]

Le 26 sept. 2009 à 06:24, Joel E. Denny a écrit :

Hi Joel!

> On Thu, 17 Sep 2009, Akim Demaille wrote:
>
> > +** 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").
>
> To fix that, use %token.

Yes, but what would you return?  %token INVALID "invalid token"?  This  
is poor, as compared to wrapping an error message as for instance we  
currently do in Bison's scanner:

  {directive} {
    complain_at (*loc, _("invalid directive: %s"), quote (yytext));
  }

> > Since the scanner probably
> > +already reported the error, we should directly enter error-recovery,
> > +without reporting the error message (i.e., YYERROR's semantics).
>
> Maybe Bison can define a special token that the scanner can return to
> induce a YYERROR?  That seems simpler than a function call.

I think both are nice.  A special token is nice when you're in the  
scanner itself.  Throwing an exception is nice in C++, especially from  
functions called from the scanner.