fibonacci implements by go, and used closure.

fib.go

package main

import (
    "fmt"
)

func fib(i, j int) func() int {
    return func() int {
        i, j = j, i+j
        return j
    }
}

func main() {
    f := fib(0, 1)
    for i := 0; i < 20; i++ {
        fmt.Println(f())
    }
}