Listens to the world while its key is in the subscriptions: an Effect Channel of messages that takes no
input and cannot fail. It either never ends (its end value is never), or ends with one last message, so
that update always learns that it is over. An ended subscription is not started again while its key
stays: only a key that goes away and comes back starts it anew.
Listens to the world while its key is in the subscriptions: an Effect
Channelof messages that takes no input and cannot fail. It either never ends (its end value isnever), or ends with one last message, so thatupdatealways learns that it is over. An ended subscription is not started again while its key stays: only a key that goes away and comes back starts it anew.