It depends on perspective. Having a finite stack is just a way of organizing a state machine. In practice all computer software is state machines. A computer is

It depends on perspective. Having a finite stack is just a way of organizing a state machine. In practice all computer software is state machines. A computer is nothing but a big state machine. A very big finite state machine. Running some software on a computer is just commanding that state machine. In computing theory we have som ideal abstractions, such as nondeterministic finite state machines, and others which are not state machines. These abstractions are just tools we use to make the design of our very big state machine programs manageable. The point of the article is that the interoperation of two or more coroutines can be modeled as an abstract state machine.