module Category = struct
  type t = Unlisted | Published | Invalid | Custom of string
  let compare = Stdlib.compare
  let of_string = function "unlisted" | "published" -> Invalid | c -> Custom c
  let to_string = function Custom c -> c | _ -> ""
end

include Category

module CategorySet = struct
  include Set.Make (Category)
  let of_stringset s = String_set.fold (fun e a -> add (Category.of_string e) a) s empty
  let of_query q = of_stringset (fst q), of_stringset (snd q)
  let predicate (inc, exl) set = not (disjoint inc set) && disjoint exl set
  let of_string x = of_stringset (String_set.of_string x)
  let to_string set =
    let f elt a =
      let s = Category.to_string elt in
      if a <> "" then a ^ ", " ^ s else s
    in
    fold f set ""
end