Module Id.Map

type key = t
type 'a t
val empty : 'a t
val find_exn : key -> 'a t -> 'a
val find_opt : key -> 'a t -> 'a option
val add : key -> 'a -> 'a t -> 'a t
val find_add : key -> ('a option -> 'a) -> 'a t -> 'a t
val iter : (key -> 'a -> unit) -> 'a t -> unit
val fold : (key -> 'a -> 'acc -> 'acc) -> 'a t -> 'acc -> 'acc