
A heating/cooling thermostat controls both a heater (during winter) and
an air conditioner (during summer). Implement a circuit that will turn on
and off the heater, air conditioning, and blower fan as appropriate. The
thermostat can be in one of two modes: heating (mode = 1) and cooling
(mode = 0). In heating mode, turn the heater on when it is too cold
(too_cold = 1) but do not use the air conditioner. In cooling mode, turn
the air conditioner on when it is too hot (too_hot = 1), but do not turn
on the heater. When the heater or air conditioner are on, also turn on
the fan to circulate the air. In addition, the user can also request the
fan to turn on (fan_on = 1), even if the heater and air conditioner are
off.

module TopModule (
  input mode,
  input too_cold,
  input too_hot,
  input fan_on,
  output heater,
  output aircon,
  output fan
);

