module type S = sig .. end
type
type +'a t
val empty : 'a t
val is_empty : 'a t -> bool
val add : key:key ->
data:'a -> 'a t -> 'a t
val find : key -> 'a t -> 'a
val remove : key -> 'a t -> 'a t
val mem : key -> 'a t -> bool
val iter : f:(key:key -> data:'a -> unit) ->
'a t -> unit
val map : f:('a -> 'b) -> 'a t -> 'b t
val mapi : f:(key -> 'a -> 'b) ->
'a t -> 'b t
val fold : f:(key:key -> data:'a -> 'b -> 'b) ->
'a t -> init:'b -> 'b
val compare : cmp:('a -> 'a -> int) ->
'a t -> 'a t -> int
val equal : cmp:('a -> 'a -> bool) ->
'a t -> 'a t -> bool