A simple state machine using recursive type in Go as shared here: http://talks.golang.org/2014/compiling.slide#6

state_machine.go

package main

import "fmt"

type F func(*State) F

type State int

func Begin(s *State) F {
	*s = 1
	return Middle
}

func Middle(s *State) F {
	*s++
	if *s >= 10 {
		return End
	}
	return Middle
}

func End(s *State) F {
	fmt.Println(*s)
	return nil
}

func main() {
	var f F = Begin
	var s State
	for f != nil {
		f = f(&s)
	}
}