OS.File
val null : fpath
val dash : fpath
val exists : fpath -> bool result
val must_exist : fpath -> fpath result
val delete : ?must_exist:bool -> fpath -> unit result
val fold : ?skip:(fpath -> bool) -> (fpath -> 'a -> 'a) -> 'a -> fpath list -> 'a result
val read : fpath -> string result
val write : fpath -> string -> unit result
val write_subst : fpath -> (string * string) list -> string -> unit result
val tmp : unit -> fpath result