Type and Function generics

typegenerics.vhdl

library ieee;
use ieee.std_logic_1164.all;
entity incrementer is
  generic (type data_type;
           function increment (x: data_type) return data_type);
  port (I : in data_type;
        O : out data_type;
        inc : in std_logic);
end;

architecture RTL of incrementer is
begin
  O <= increment(I) when inc = '1';
end;

library ieee;
use ieee.std_logic_1164.all;
entity typegenerics is
  port (I : in unsigned(7 downto 0);
        O : out unsigned(7 downto 0);
        ena : in std_logic);
end;
architecture RTL of typegenerics is
  function add_one (b : in unsigned(7 downto 0)) return unsigned(7 downto 0) is
  begin
    return (b + 1);
  end;
begin

  incr_inst : entity work.incrementer
  generic map ( data_type => unsigned(7 downto 0),
                increment => add_one )
  port map ( I => I, O => O, inc => ena );
end;