include module type of Stdlib.Hashtbl

(** [map f m] maps the values in [m] by [f]. This involves converting [m] to
    a {!Seq}, mapping the values by [m], then constructing the new hashtable
    from the resulting sequence. *)
val map : ('a -> 'b) -> ('k, 'a) t -> ('k, 'b) t

(** [group_by k l] groups the values in [l] by the keys assigned by [k] into
    a hashtable. *)
val group_by : ('a -> 'k) -> 'a list -> ('k, 'a list) t
