## listat
### Instructions
Write a function `ListAt` that takes a pointer to the list `l` and an `int pos` as parameters. This function should return the `NodeL` in the position `pos` of the linked list `l` .
- In case of error the function should return `nil` .
### Expected function and structure
```go
type NodeL struct {
Data interface{}
Next *NodeL
}
func ListAt(l *NodeL, pos int) *NodeL{
}
```
### Usage
Here is a possible program to test your function :
```go
package main
import (
"fmt"
"piscine"
)
func main() {
link := & piscine.List{}
piscine.ListPushBack(link, "hello")
piscine.ListPushBack(link, "how are")
piscine.ListPushBack(link, "you")
piscine.ListPushBack(link, 1)
fmt.Println(piscine.ListAt(link.Head, 3).Data)
fmt.Println(piscine.ListAt(link.Head, 1).Data)
fmt.Println(piscine.ListAt(link.Head, 7))
}
```
And its output :
```console
$ go run .
1
how are
< nil >
$
```
