Theoretically speaking, any machine that keeps a fixed (finite) amount of state is a finite state machine. Once you recognize that, you will realize that you ha

Theoretically speaking, any machine that keeps a fixed (finite) amount of state is a finite state machine. Once you recognize that, you will realize that you have written lots of them without even trying. If a problem inherently requires a fixed amount of state, writing a finite state machine is virtually inevitable. So it's not really a choice of whether to write a finite state machine; it's a choice of how you want it to look; it's a question of style. The state machine style assigns a name to each state, and makes the transitions very obvious. Co-routines can be finite state machines, quite clearly. You could argue that they do not follow the state machine style, though.