module Bag:A bag is a data structure like a set, except that:sig..end
It doesn't require anything (hashable, comparable) of elements in the bag.
Duplicates are allowed.
Addition and removal are constant time.
module Elt:sig..end
type 'a t
include Container.S1
val invariant : 'a t -> unitval create : unit -> 'a tcreate () returns an empty bag.val add : 'a t -> 'a -> 'a Elt.tadd t v adds v to the bag t, returning an element that can
later be removed from the bag. add runs in constant time.val remove : 'a t -> 'a Elt.t -> unitremove t elt removes elt from the bag t, raising an exception if elt
is not in the bag. remove runs in constant time.some_elt t returns some element in the bag.val some_elt : 'a t -> 'a Elt.t optionval remove_one : 'a t -> 'a optionremove_one t removes some element from the bag, and returns its value.
remove_one runs in constant time.val clear : 'a t -> unitclear t removes all elements from the bag. clear runs in O(1) time.val find_elt : 'a t -> f:('a -> bool) -> 'a Elt.t optionfind_elt t ~f looks at elements in the bag one-by-one until it finds one
elt such that f (Elt.value elt), in which case it returns Some elt.
If there is no element satisfying f, then find_elt returns None.val until_empty : 'a t -> ('a -> unit) -> unituntil_empty t f repeatedly removes a value v from t and runs f v,
continuing until t is empty. Running f may add elements to t if it
wants.val sexp_of_t : ('a -> Std_internal.Sexp.t) -> 'a t -> Std_internal.Sexp.t