gistfile1.txt

  module Pool = struct
    module TxSet = Set.Make (KEY)

    let data = ref TxSet.empty

    let add ~tx =
      match is_valid ~tx with
      | false -> ()
      | true -> data := TxSet.add tx !data

    let remove ~tx = data := TxSet.remove tx !data
    let mem ~tx = TxSet.mem tx !data
    let elements = TxSet.elements !data
  end