sig
type t = string
val compare : t -> t -> int
val string : t -> t
val substring : t -> int -> int -> t
external channel : in_channel -> int -> t = "caml_md5_chan"
val file : t -> t
val output : out_channel -> t -> unit
val input : in_channel -> t
val to_hex : t -> t
val from_hex : t -> t
end