`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`