anchor.diff:  
   parse_req_field(Code, ParseValue, L) ->
       case parse_opt_field(Code, ParseValue, L) of
  -        {'undefined', _Rest} -> error({'missing_field', Code});
  +        {'undefined', _Rest} -> throw_error({'missing_field', Code});
           X -> X
       end.
   
  
positive.code:     {{FieldCode, FieldValue}, _Rest} = parse_field(Bytes),
      case FieldCode of
          1 -> FieldValue;
          _ -> error('invalid_toplevel_header')
      end.
  
  
  
negative.code:     find_fields(Code, T, Accu, [H | Rest]).
  
  
  -spec throw_error/1 :: (any()) -> no_return().
  
  throw_error(X) ->
      throw({'piqirun_error', X}).
  
  
  