local
    fun drop_string n st = foldr (fn (x,y) => str(x) ^ y) "" (List.drop((explode st),n))
    fun index _ [] = ~1
        | index n (x::xs) = if n = x then 0 else
            let
                val l = (index n xs)
            in
                if (l = ~1) then l else l + 1
            end
    fun fraction2RepeatingDecimal_aux 0 _ _ output = output
        | fraction2RepeatingDecimal_aux n m lst output =
            let
                val quation = ((n*10) div m)
                val reminder = ((n*10) - (quation*m))
                val l = (index reminder lst)
            in
                if (l = ~1) then
                    fraction2RepeatingDecimal_aux reminder m (lst @ [reminder]) (output ^ Int.toString(quation))
                else if String.substring(output, l, 1) <> Int.toString(quation) then
                    String.substring(output, 0, l + 1) ^ "(" ^ Int.toString(quation) ^ ")"
                else String.substring(output, 0, l) ^ "(" ^ (drop_string l output) ^ ")"
            end
in
    fun fraction2RepeatingDecimal 0 _ = "0.0"
        | fraction2RepeatingDecimal n m = "0." ^ (fraction2RepeatingDecimal_aux n m [] "")
end;