> For the complete documentation index, see [llms.txt](https://ploegert.gitbook.io/til/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ploegert.gitbook.io/til/programmy/elixir/check-list-membership.md).

# Check List Membership

You can use the [`in` operator](https://hexdocs.pm/elixir/operators.html) to check if something appears in a list. This is a handy way of checking if a variable is one of a few acceptable or expected values.

For instance, a common DateTime comparison pattern relies on this to check if a DateTime is `>=` or `<=` to another DateTime.

```elixir
{:ok, datetime} = DateTime.from_naive(~N[2016-05-24 13:26:08.003], "Etc/UTC")

DateTime.compare(datetime, DateTime.utc_now()) in [:lt, :eq]
```

Alternatively, you can check that something does not have membership in a list by also including the `not` operator.

```elixir
DateTime.compare(datetime, DateTime.utc_now()) not in [:lt, :eq]
```