package main

// fib returns a function that returns
// successive Fibonacci numbers.
func fib() func() int {
    a, b := 0, 1
    return func() int {
        a, b = b, a+b
        return b
    }
}

func main() {
    f := fib()
    // Function calls are evaluated left-to-right.
    println(f(), f(), f(), f(), f())
}