advent-of-code-2021/day-05/lib/bit_extra.sml

structure Bit = struct
    fun to_decimal (bit, ind) =
        (* ind: the index of the bit counted from least significant bit to most
           significant bit (MSB) *)
        bit * IntExtra.expt (2, ind);

    fun bits_to_decimal bit_vector =
        let
            val len = Vector.length bit_vector;
            fun iter (bits, ind, acc) =
                if ind < len
                then
                    let
                        val bit = Vector.sub(bits, ind);
                        val position = (len - 1) - ind;
                        val decimal_value = to_decimal (bit, position);
                    in
                        iter (bits, ind + 1, acc + decimal_value)
                    end
                else
                    acc;
        in
            iter (bit_vector, 0, 0)
        end;

    fun bit_list_from_string str =
        map (fn c =>
                case c of
                    #"1" => 1
                  | #"0" => 0
                  | _ => raise Fail "unrecognized bit value")
            (String.explode str);
end;