module Subscriber:sig..end
subscribe_exn t ~f causes f to be applied to all values subsequently written to
t (or if t is unstarted, to prior values as well). subscribe_exn raises if it
is called on a started bus with not can_subscribe_after_start. The function f is
allowed to call other Bus functions on t, e.g. write, subscribe_exn, or
unsubscribe.
If f raises, the corresponding subscriber will be automatically unsubscribed, and
the exception will be sent to the monitor in effect when subscribe_exn was called.
Once unsubscribe t subscriber is called, f will never be called again.
type 'a t
val sexp_of_t : ('a -> Sexplib.Sexp.t) -> 'a t -> Sexplib.Sexp.t