code: protected int findVarDef( String name)
      {
      int varCount = name==null? 0 : vars_.size();
      int i;
      for( i = 0; i < varCount && !name.equals( vars_.get(i).getName()); i++);
      return i < varCount? i : -1;
      }
docs: Returns the index of the variable definition with the given name.