Re: help with an if rule!

[Hans Aberg]

On 14 Aug 2005, at 21:43, Roberto Mandall wrote:

> thx for the answer,but i still get errors, i guess i just do not  
> undertsnad bison well enough.
> i have this now:
> %nonassoc ELSE
> %nonassoc THEN
>
> open_if_statement : IF boolean_expression {} THEN  statement {/}
>            |IF boolean_expression  {} THEN closed_statement  ELSE   
> open_statement{} ;
>           closed_if_statement : IF boolean_expression {} THEN  
> closed_statement  ELSE closed_statement {};
>
>
> i get this:
> bison -d --debug -v parser.y
> parser.y: conflicts: 1 reduce/reduce
>
> parser out put says:
> State 140 conflicts: 1 reduce/reduce
>
> state 140 has got this:
>
> state 140
>
>   38 statement: closed_statement .
>   54 open_if_statement: IF boolean_expression THEN  
> closed_statement . @13 ELSE open_statement
>   56 closed_if_statement: IF boolean_expression THEN  
> closed_statement . @14 ELSE closed_statement
>
>    ELSE      reduce using rule 53 (@13)
>    ELSE      [reduce using rule 55 (@14)]
>    $default  reduce using rule 38 (statement)
>
>    @13  go to state 162
>    @14  go to state 163
>
> can any1 plz tell me what am i doing wrong? i do really need those  
> semantic rules after the "THEN closed_statement"

You have put a series of mid-rule actions, which causes reduce/reduce  
conflicts, as implemented as an empty rule. The token precedences  
just looks at the tokens immediately before and after the ".", and  
cannot resolve that. So you have to remove those mid-rule actions,  
putting the actions in the rules of the grammar variables preceding  
them.

  Hans Aberg