[Go] Higher-order function: enumerate

package main

import (
    "fmt"
)

type Tuple struct {
    Index   int
    Element int
}

func enumerate(m []int) func() (Tuple, bool) {
    i := -1
    return func() (Tuple, bool) {
        i += 1
        if i < len(m) {
            return Tuple{Index: i, Element: m[i]}, true
        } else {
            return Tuple{Index: i, Element: 0}, false
        }
    }
}

func main() {
    m := []int{10, 20, 30, 40, 50}

    iter := enumerate(m)

    for {
        out, ok := iter()
        if !ok {
            break
        }

        fmt.Println(fmt.Sprintf("%d: %d", out.Index, out.Element))
    }
}