Re: Tree-like construction while parsing the input file

[Hans Aberg]

On 11 Jan 2009, at 18:37, Ilyes Gouta wrote:

> > Then the parse tree of those before will be constructed before  
> > those latter.
> > In your example, item_declaration will be constructed before  
> > item_list, so
> > one can have actions
> > item_declaration {...} item_list {...}
> > Here, the first action {...} can only use the item_declaration  
> > value, but
> > the second can use all that comes before. - See the Bison manual for
> > details.
>
> At the end of that rule, the value of item_declaration is $1 and  
> item_list
> is $2 and the overall return value is $$. What would be the value of
> item_declaration in my action if I put the latter just straight  
> after it
> (not at the end of the rule)?

See the Bison manual for details. They are implemented by inserting an  
implicit non-terminal with an empty rule and an action. Given a rule
  x: a {b} c {d} e {f}
then the action {d} can use $1 from a, $2 from the $$ that {b}  
returns, and $3 from c, but not $4 (it should be $$ inside d) or $5 -  
those can only be used in the action {f}.

  Hans