Re: bison location tracking ..

[Vardhan Varma]

--- Hans Aberg <address@hidden> wrote:
> >> I've defined yylocation type to struct { offset,
> size
> >> }, and all that's working great.
> >>
> >> my problem is blank RHS .. offset gets set to
> zero.
> >> so  in rule like
> >> atoms:   /* blank */
> >>      | atoms ATOM
> >> since first blank rule gets fired, the offset &
> size
> >> are set to zero.
> >>
> >> Do you have any workaround/solution for this
> 
Well, I figured out this function does the right thing
for me:
typedef struct YYLTYPE
{
  int  start;
  int  finish;
} YYLTYPE;

# define YYLLOC_DEFAULT(Current, Rhs, N)  
updyylval(&Current, Rhs, N);


void  updyylval(YYLTYPE *Current, YYLTYPE Rhs[], int
N) {
    int i;

    Current->start = Current->finish = -1;

    for ( i = 1 ; i <= N ; i ++ )
        if ( Rhs[i].start != -1 ) {
            Current->start = Rhs[i].start;
            break;
        }

    for ( i = N ; i >= 1 ; i -- )
        if ( Rhs[i].finish != -1 ) {
            Current->finish = Rhs[i].finish;
            break;
        }
    //dump(Current);

}


> The Bison location tracking feature is currently
> left essentially
> unsupported, in part because no-one seems to agree

  Well, It's unsupported, but thankfully not broken. 

> on what a suitable
> location tracking ought to be. The Bison default
> location tracking rule
> attempts to pinpoint the total area of the current
> grammar symbol. So, for
> the empty symbol, there is no location yet.

   I'm newbie, but somehow my func above seems to be
working for empty RHS also. ( make them -1/-1 , since
N is zero ). 

> 
> A more prudent location tracking method for use with
> error reporting seems
> to be to keep track of the location of the current
> lookahead token, i.e.,
> its line number and its location on the line. Then
> that must be implemented
> explicitly. Perhaps a tweak of the skeleton file
> might help.
> 
>   Hans Aberg

  The perfect way of doing thins is certainly welcome,
but lesser-learned of the tribes must use what's
availble today.

--Regards
--Vardhan

> 
> 


=====
--
Vardhan


        
                
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