qustavo / go-fsm-example

An example FSM implementation in Go

go-fsm-example

An example FSM implementation in Go using State functions (or what I understood from Lexical Scanning in Go)

The idea is simple, each state function returns the next state.

// stateFn represents the state of the machine
// as a function that returns the next state.
type stateFn func(*fsm) stateFn

Then each state is defined as a function that receives a *fsm and return a stateFn

func idleState(f *fsm) stateFn {
	f.code = ""
	fmt.Printf("Enter code: ")
	return readState
}

In this example I'm creating a fsm that verify some secret code.

To represent the done state a stateFn must return nil and the machine stops, the main loop looks like:

func (self *fsm) run() {
	self.reader = bufio.NewReader(os.Stdin)
	for s := idleState; s != nil; {
		s = s(self)
	}
}

And that's it.