VHDL "EVENT" Problem

Hello, I'm a beginner for using Quartus II. I have an error in this VHDL code

--------------------------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity Test is

port(clk : in std_logic;

preset : in std_logic;

flag : in std_logic;

out : out std_logic_vector(15 downto 0);

done : out std_logic

);

end Test;

architecture RTL of Test is

signal d :std_logic_vector(15 downto 0);

signal q :std_logic_vector(15 downto 0);

signal I :std_logic_vector(15 downto 0) := "0111010101001101";

signal flag_sgl : std_logic ;

signal done_sgl, VI, : std_logic;

begin

process(clk,flag)

begin

if(preset= '0') then

flag_sgl <= '0';

done_sgl <= '0';

VI <= '1';

elsif (clk'event and clk='1') then

VI <= '0';

if (flag_sgl = '1')then

flag_sgl <= '0';

done <= not(done_sgl);

done_sgl <= not(done_sgl);

out <= q(15 downto 0);

q <= d;

end if;

end if;

if (flag'event ) then

flag_sgl <= '1';

end if;

end process ;

------------------------

d(0) <= I(0) when VI = '1' else q(1) ;

d(1) <= I(1) when VI = '1' else q(2) ;

d(2) <= I(2) when VI = '1' else q(0) xor q(3) ;

d(3) <= I(3) when VI = '1' else q(4) ;

d(4) <= I(4) when VI = '1' else q(5) ;

d(5) <= I(5) when VI = '1' else q(6) ;

d(6) <= I(6) when VI = '1' else q(0) xor q(7) ;

d(7) <= I(7) when VI = '1' else q(8) ;

d(8) <= I(8) when VI = '1' else q(9) ;

d(9) <= I(9) when VI = '1' else q(0) xor q(10);

d(10) <= I(10) when VI = '1' else q(11) ;

d(11) <= I(11) when VI = '1' else q(0) xor q(12);

d(12) <= I(12) when VI = '1' else q(13) ;

d(13) <= I(13) when VI = '1' else q(14);

d(14) <= I(14) when VI = '1' else q(0) xor q(15);

d(15) <= I(15) when VI = '1' else q(0);

end architecture RTL;

-----------------------------------------------------------------------------------------

I got a problem in the "RED" color line.

I would like "flag_sgl" change value to '1', everytime that input signal "flag" change its value.

Are there any way for detecting "flag" changing without using 'EVENT?

Thank you in advance ^^