[A Tour of Go] Exercise: Fibonacci closure

https://go.dev/tour/moretypes/26

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	f1, f2 := 0, 1
	return func() int {
		res := f1
		f1, f2 = f2, f1 + f2
		return res
	}
}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}