You can search for identifiers within the package.
in-package search v0.2.0
val mkdir : string -> (unit option -> unit) -> unit
val rmdir : string -> (unit option -> unit) -> unit
val readdir : string -> (string array option -> unit) -> unit
val stat : string -> 'a option
val open_ : string -> string -> (int option -> unit) -> unit
val close : int -> (unit option -> unit) -> unit
val read : int -> Io_buffer.t -> (int -> unit) -> unit
val write : int -> Io_buffer.t -> (int -> unit) -> unit