val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
type ic = Lwt_io.input_channel
type oc = Lwt_io.output_channel
val iter : ('a -> unit t) -> 'a list -> unit t
val read_line : ic -> string option t
val read : ic -> int -> string t
val read_exactly : ic -> int -> string option t
val write : oc -> string -> unit t