let commaize s =
        let rec insert_commas list = 
            match List.length list with
            | 0 -> []
            | 1 -> list
            | 2 -> list.Head :: " and " :: list.Tail
            | _ -> list.Head :: ", " :: insert_commas list.Tail

        String.concat "" (Seq.toList s |> insert_commas )