Re: LALR : How it work during parsing time with empty rule ? what to do to the stack?

[Hans Aberg]

On 12 Sep 2005, at 23:31, Baldurien (club internet) wrote:

> I've  made  a  little  parser in PHP based on bison output file, and I
> experiment a little problem :
>
> When I have to reduce, saying by rule X : Y '+' X I know I have to pop
> 3  times, but what happens when the rule is simply X : /* empty */ ? I
> can't pop at all, so what should I do?

Just don't pop. If  s  is the state on top of the state stack, the  
total effect is that the state goto(s, X) is pushed onto it. If you  
have a stack for non-terminals and terminals, which the Bison  
generated parser doesn't, then X will be pushed onto that. The rule  
action is executed.

  Hans Aberg