.. efun:: int notify_fail(string str)
  int notify_fail(closure cl)

  Store :arg:`str` as the error message given instead of the default message "What ?". The result is always 0.

  If a closure is given, it is executed to return the error message string, but not before all attempts to execute the commandline failed (read: not at the time of the call to :efun:`notify_fail`). The closure receives as argument the original commandgiver; usually it is identical to ``this_player()``, unless :hook:`H_MODIFY_COMMAND` changed that.

  If :efun:`notify_fail` is called more than once for this command, only the last call will be used. However, calls to :efun:`notify_fail` in nested commands have no effect on this command.

  .. usage::

    The idea of this function is to give better error messages instead of simply 'What ?'.

    A naive to write a message when a simple command fails is::

      write(message);
      return 1;

    Unfortunately, this message will print before other objects get a chance to evaluate the verb. It is better to use::

      return notify_fail(message);

    This way, the driver only prints a single failure message--and only if the verb fails all of the objects that get a chance to handle it.

  :history 3.2.6 changed: return type from void to int.
  :history 3.2.7 changed: notify-fail settings are saved over nested commands, and NPCs can see their notify-fail messages.

  .. seealso:: :efun:`add_action`, :efun:`command`, :efun:`query_verb`, :efun:`query_command`, :efun:`query_notify_fail`, :overview:`hook`