module Equeue:sig..end
Equeue implements generic event queues. An event system 
 consists of an event queue, a list of event handlers, and an 
 event source. The queue has FIFO semantics, i.e. the first event
 is processed next, and new events are appended to its end. When
 an event is delivered to an event handler, all handlers are tried
 until a handler accepts the event (or the event is dropped if no
 such handler can be found). See below how a handler can indicate
 whether to accept or reject an event.
 When the queue is empty, the event source is called once. The source
 can add events to the queue, in order to continue event processing.
 If the queue remains empty, the execution of the event system
 stops.
 The module can be used in multi-threaded program provided no
 event system is shared by several threads, or if so, access to
 functions is serialized.
type 'a t 
exception Reject
exception Terminate
exception Out_of_handlers
run when the event source adds new events to the queue
 but there are no event handlers to process themval create : ?string_of_event:('a -> string) -> ('a t -> unit) -> 'a t'a t -> unit is the
 event source. The source can call add_event to put new events
 into the queue.
string_of_event : Optionally, one can pass a printer for events.
   This has only an effect for debugging output.val add_event : 'a t -> 'a -> unitval add_handler : 'a t -> ('a t -> 'a -> unit) -> unitAn event handler is called with the event system and the event as arguments. The handler can return in various ways:
Reject: The event is rejected by the handler. The other
   handlers are asked to process the event.Terminate: The event is accepted, but the handler is
   terminated, i.e. will never be called again.run.val run : 'a t -> unitrun invocation and all later added events are
 gone through. Each event is presented to the handlers until one
 handler accepts the event. Events rejected by all handlers are
 dropped silently. If there is no pending event the default event
 source is called once. If there are still no events the system stops
 and returns. If there are events to process but no handlers which
 can do them all events are silently dropped, and the default event
 source is called once.
 The exception Out_of_handlers is raised if there are events but no
 handlers after the event source has been called. This is considered
 as a programming error, and would cause infinite looping if not
 detected.
Note that there is an implicit order among the handlers which is simply the order the handlers have been added to the system. This means that you can set a fallback handler which catches any unprocessed event by adding it last.
Note that the events are processed in the order they happen. There is no mechanism to assign priorities to events.
 Handlers are allowed to raise arbitrary exceptions. Exceptions other
 than Reject and Terminate are not caught, so the caller has to do this
 if appropriate. It is possible to restart an event system by just
 calling run again.
val is_running : 'a t -> boolmodule Debug:sig..end