Declare Listener as the owner of the channel. Unlike a
channel opened using listen/2,
channels that have an owner can terminate the channel. This is commonly
used if an object is listening to broadcast messages. In the example
below we define a‘name-item' displaying the name of an identifier
represented by the predicate name_of/2.
:- pce_begin_class(name_item, text_item).
variable(id, any, get, "Id visualised").
initialise(NI, Id:any) :->
name_of(Id, Name),
send_super(NI, initialise, name, Name,
message(NI, set_name, @arg1)),
send(NI, slot, id, Id),
listen(NI, name_of(Id, Name),
send(NI, selection, Name)).
unlink(NI) :->
unlisten(NI),
send_super(NI, unlink).
set_name(NI, Name:name) :->
get(NI, id, Id),
retractall(name_of(Id, _)),
assert(name_of(Id, Name)),
broadcast(name_of(Id, Name)).
:- pce_end_class.
listen(+Listener,
+Template, :Goal)