Re: Odd parser behaviour

[Hans Aberg]

On 25 Sep 2006, at 09:01, Heiko Wundram wrote:

> Bison reduces everything as far as possible before erroring out  
> (that's a
> general properly of LALR(1)-parsers), but here, there's absolutely  
> no rule
> for it to do what you want, so the error occurs on the shift on the  
> expected
> E.

Actually, LR(1) issues an error immediately on seeing the erroneous  
token. LALR(1) compacts certain LR(1) states, and as a consequence of  
that, may perform additional reductions. But there is no general rule  
when this occurs, as far as I know.

So if the original question is over shaky error handling, that is  
just a part of the LALR(1) that Bison uses. The only way to cope with  
it, for now, is trial and error.

It has been discussed to give Bison a LR(1) parser option, which it  
does not have now, where better error handling is one motivation.

  Hans Aberg