# A practical List.push example / understanding "null" in List usage
**URL:** https://forum.dfinity.org/t/a-practical-list-push-example-understanding-null-in-list-usage/26213
**Category:** Language Support
**Created:** [January 5, 2024, 12:26am UTC](https://forum.dfinity.org/t/a-practical-list-push-example-understanding-null-in-list-usage/26213 "2024-01-05T00:26:01Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@nolma](https://forum.dfinity.org/u/nolma)
#### Post date: [January 5, 2024, 12:26am UTC](https://forum.dfinity.org/t/a-practical-list-push-example-understanding-null-in-list-usage/26213/1 "2024-01-05T00:26:01Z")
The examples from the documentations use “null” in place of lists for operations like:
```auto
List.push(0, null) // => ?(0, null);
```
the resulting value doesn’t, at a glance, appear to be a List. This was confusing. I would like to see more practical examples for the List operations.
I’m also wondering, is “null” interpreted as an empty list?
What does “?(0, null);” mean?
I would expect something like:
```auto
var numbers = List.nil;
numbers := List.append(1, numbers); //List[1]
```
---
### Author:  [@rossberg](https://forum.dfinity.org/u/rossberg)
#### Post date: [January 5, 2024, 10:40am UTC](https://forum.dfinity.org/t/a-practical-list-push-example-understanding-null-in-list-usage/26213/2 "2024-01-05T10:40:06Z")
The List type is [represented](https://github.com/dfinity/motoko-base/blob/master/src/List.mo#L22) as an optional pair of a value and a tail list:
```auto
public type List = ?(T, List);
```
This effectively is a single-linked list, where `null` (the empty option) represents the empty list.
```auto
let a = null; // [], same as List.nil
let b = ?(1, null); // [1]
let c = ?(1, ?(2, null)); // [1, 2]
let d = ?(0, c); // [0, 1, 2], same as List.push(0, c)
```
`List.append` on the other hand concatenates two lists, so your example won’t type-check. This does:
```auto
let e = List.append(d, d); // [0, 1, 2, 0, 1, 2]
```