include Set.Make(String)

let list_of_csv x = Str.(split (regexp " *, *")) (String.trim x)
let of_string x = of_list (list_of_csv x)
let to_string ?(pre="") ?(sep=", ") s =
  let j a x = match a, x with "", _ -> x | _, "" -> a | _ -> a ^ sep ^ x in
  fold (fun x acc -> j acc x) s pre

let query string =
  let partition (include_set, exclude_set) elt =
    if String.get elt 0 = '!' then (include_set, add String.(sub elt 1 (length elt - 1)) exclude_set)
    else (add elt include_set, exclude_set) in
  List.fold_left partition (empty, empty) @@ list_of_csv string

let predicate (inc, exl) set = not (disjoint inc set) && disjoint exl set