Why FSMs?
  Easy way to think about control structure:
    Nodes = actions, Transitions = reactions
  Separates control (links) from function (nodes)
  Easy way to handle fork/join, randomness, timeouts
  Easy to trace execution



Events: 
  internally generated: completion, success/failure
  external: taps, text messages

show how transitions become active, listen, fire...

FSMs
  notation
  Event and EventListener
  handling failures, completions, and cancellations

  runfsm
  genfsm
  tracefsm