func ping(x:Int)->[Text]
	if x > 0
		return ["ping: {x}"] ++ pong(x-1)
	else
		return ["ping: {x}"]

func pong(x:Int)->[Text]
	if x > 0
		return ["pong: {x}"] ++ ping(x-1)
	else
		return ["pong: {x}"]

>> ping(3)
= ["ping: 3", "pong: 2", "ping: 1", "pong: 0"]