function yieldtst, file, yield=yield
   
       nl = 0L  &  tmp=''
       openr,lun,file,/get_lun 
       on_ioerror,NOASCII 
       while not eof(lun) do begin 
           readf,lun,tmp 
           nl = nl + 1 
           if keyword_set(yield) then if (nl mod 30) eq 0 then yield
       endwhile 
       close,lun 
       free_lun,lun 
       NOASCII:
       if keyword_set(yield) then yield, /destroy 
       return,nl
   
   end