Event

`sig
type 'a channel
val new_channel : unit -> 'a Event.channel
type +'a event
val send : 'a Event.channel -> 'a -> unit Event.event
val receive : 'a Event.channel -> 'a Event.event
val always : 'a -> 'a Event.event
val choose : 'a Event.event list -> 'a Event.event
val wrap : 'a Event.event -> ('a -> 'b) -> 'b Event.event
val wrap_abort : 'a Event.event -> (unit -> unit) -> 'a Event.event
val guard : (unit -> 'a Event.event) -> 'a Event.event
val sync : 'a Event.event -> 'a
val select : 'a Event.event list -> 'a
val poll : 'a Event.event -> 'a option
end`