package main import "fmt" // fibonacci is a function that returns // a function that returns an int. func fibonacci() func() int { f0, f1 := 0, 1 return func() int { f := f0 f0, f1 = f1, f+f1 return f } } func main() { f := fibonacci() for i := 0; i < 10; i++ { fmt.Println(f()) } }