sort
	CardinalDirection = struct north | east | south | west;


sort
	Colour = struct red | green | yellow;

map
	nextColour: Colour -> Colour;

eqn
	nextColour(red) = green;
	nextColour(green) = yellow;
	nextColour(yellow) = red;

act
	show : CardinalDirection # Colour;

proc
	TrafficLight(direction : CardinalDirection) = TF(direction, red);

	TF(direction : CardinalDirection, colour : Colour) =
		show(direction, colour).
		TF(direction, nextColour(colour))
	;

		

init
	TrafficLight(north) || TrafficLight(east) || TrafficLight(south) || TrafficLight(west)
;