ocaml中集合的定义

module Set : sig
  type ('a, 'b) t
  val empty : ('a, 'b) t
  val is_empty : ('a, 'b) t -> bool
  val mem : 'a -> ('a, 'b) t -> bool
  val add : 'a -> ('a, 'b) t -> ('a, 'b) t
  val singleton : 'a -> ('a, 'b) t
  val remove : 'a -> ('a, 'b) t -> ('a, 'b) t
  val union : ('a, 'b) t -> ('a, 'b) t -> ('a, 'b) t
  val inter : ('a, 'b) t -> ('a, 'b) t -> ('a, 'b) t
  val diff : ('a, 'b) t -> ('a, 'b) t -> ('a, 'b) t
  val compare : ('a -> 'a -> int) -> ('a, 'b) t -> ('a, 'b) t -> int
  val equal : ('a -> 'a -> bool) -> ('a, 'b) t -> ('a, 'b) t -> bool
  val subset : ('a, 'b) t -> ('a, 'b) t -> bool
  val iter : ('a -> unit) -> ('a, 'b) t -> unit
  val map : ('a -> 'c) -> ('a, 'b) t -> ('c, 'b) t
  val fold : ('a -> 'b -> 'b) -> ('a, 'c) t -> 'b -> 'b
  val for_all : ('a -> bool) -> ('a, 'b) t -> bool
  val exists : ('a -> bool) -> ('a, 'b) t -> bool
  val filter : ('a -> bool) -> ('a, 'b) t -> ('a, 'b) t
  val partition : ('a -> bool) -> ('a, 'b) t -> ('a, 'b) t * ('a, 'b) t
  val cardinal : ('a, 'b) t -> int
  val elements : ('a, 'b) t -> 'a list
  val min_elt : ('a, 'b) t -> 'a
  val max_elt : ('a, 'b) t -> 'a
  val choose : ('a, 'b) t -> 'a
  val split : 'a -> ('a, 'b) t -> ('a, 'b) t * bool * ('a, 'b) t
end

module IntSet = Set.Make(struct type t = int let compare = compare end)

let s = IntSet.empty
let s' = IntSet.add 1 s
let s'' = IntSet.add 2 s'
let s''' = IntSet.remove 1 s''
let b = IntSet.mem 1 s''
let c = IntSet.cardinal s''