pkg event =
	type hub(@ev) = struct
		/* opaque */
	;;
	type sendtag = void#

	/* blocks until an event is ready, then returns it. */
	generic wait	: (h : hub(@ev)# -> @ev#)

	/* 
	 * chains one event source into another: when an event on slave 's' is
	 * available, cvt(wait(s)) is fired on the master.
	 */
	generic chain	: (m : hub(@mev)#, s : hub(@sev)#, cvt : (e : @sev -> @mev) -> void)
	/* adds a source; the source should block until the event is ready. */
	generic add	: (h : hub(@ev)#, fn : (-> @ev) -> void)
	/* adds an fd-based source; this may be more convenient on some systems. */
	generic addfd	: (h : hub(@ev)#, fd : std.fd, fn : (fd : std.fd -> @ev) -> void)
;;