Partial failure in record type update

part_fail.vhd

library ieee;
use ieee.std_logic_1164.all;
library ps;
use ps.hex_conv.all;

entity light is
  port(
    clock_50               : in  std_logic;
    hex0, hex1, hex2, hex3 : out std_logic_vector(0 to 6);
    key                    : in  std_logic_vector(0 to 3);
    sw                     : in  std_logic_vector(0 to 9);
    ledr                   : buffer std_logic_vector(0 to 9);
	  ledg                   : buffer std_logic_vector(0 to 7);
		btn                    : in std_logic_vector(0 to 3)
  );
end light;

architecture arch of light is
  subtype hex_digit is std_logic_vector(0 to 6);
	type hex_digit_array is array(natural range<>) of hex_digit;
  constant digits : hex_digit_array :=
		(
			"0000001", "1001111", "0010010", "0000110", "1001100",
			"0100100", "0100000", "0001111", "0000000", "0000100"
		);
	subtype digit is integer range 0 to 9;
	
	function get_hex_digit(d:digit) return hex_digit is
	begin
		return digits(d);
	end function;
	
	type temp_unit is (celcius, fahrenheit);
	type hex_temp_array is array(temp_unit range <>) of hex_digit;
	constant temp_char_array : hex_temp_array(celcius to fahrenheit) :=
	  ("0110001", "0111000");
		
		
	type temp_setting is record
		temp: integer range 0 to 99;
		unit : temp_unit;
	end record;
	
	signal setting : temp_setting := (25, celcius);
	
begin
	hex3 <= get_hex_digit(setting.temp / 10);
	hex2 <= get_hex_digit(setting.temp rem 10);
	hex1 <= "0011100";
	hex0 <= temp_char_array(setting.unit);
	
	warmer: process(btn)
	begin
		if (btn(0)'event and btn(0) = '1') then
			setting.temp <= 0;
		end if;
	end process;
	
	process(sw)
	begin
		if (sw(0) = '0') then
			setting.unit <= celcius;
		else
			setting.unit <= fahrenheit;
		end if;
	end process;

end architecture arch;