Marxian Economics is certainly a theory...that doesn't mean it works or is agreeable to any one with half a brain...
http://www.investopedia.com/terms/m/marxian-economics.asp
We'll I guess that you could argue that USSR had an economy. Certainly not comparable to a Free Market thriving economy like in the US.... which helped us to win the Cold War.
Communism strangles innovation and kills incentive and motivation which produce a healthy economy. So in that respect and an analogy: a dying man lying in his death bed is still alive. :)