VHDL: recursive n bit comparator

I have to create a n bit comparator (under respect of n = 2**k) in VHDL with recursion. Since the necassary chapter is taken after the christmasbreak, I have no lecture notes. My idea was using the generic statement like this:. I thought I could use the generic statement, like this:

entity comperator is
    generic (k: integer := 0);
    port(a, b: std_logic_vector(2**k-1 downto 0);
         c: out std_logic_vector (1 downto 0));
end;

architecture recursive of comperator is 
  signal e,d: std_logic_vector(1 downto 0);

begin
    p2: if k /= 0 generate
      d1 : entity comperator
           port map (a(2**k-1 downto 2**(k-1)), b(2**k-1 downto 2**(k-1)), d);

I made with testbench a simulation but I got strange error reports, something like this: "sem_parenthesis_name: cannot handle IIR_KIND_COMPONENT_INSTANTIATION_STATEMENT (design.vhd:19:11)"

If you need the hole code: https://www.edaplayground.com/x/2RuY

I have no idea why the code doesn't work. Has anyone an idea?

Greedings, What's in the box

Solution

I've found the mistake, now it works. If someone has the same or similar problem, here is the link to the working source code: https://www.edaplayground.com/x/2RuY