Accessing a single element of a list by index

Getting an element from a list using an index is a common language idiom.

In ruby you would use the squares [] method (similar to Java, C#, etc.).

> [:a, :b, :c, :d][2]
:c

But Elixir is not object oriented and instead provides the Enum module that has many functions that can operate on a list. Three functions return an element by index.

iex > Enum.at([:a, :b, :c, :d], 2)
:c
iex > Enum.fetch([:a, :b, :c, :d], 2)
{ :ok, :c }
iex > Enum.fetch!([:a, :b, :c, :d], 2)
{ :ok, :c }

They behave differently when the index doesn't correspond to the list.

iex > Enum.at([:a, :b, :c, :d], 9999)
nil
iex > Enum.fetch([:a, :b, :c, :d], 9999)
:error
iex > Enum.fetch!([:a, :b, :c, :d], 9999)
** (Enum.OutOfBoundsError) out of bounds error
    (elixir) lib/enum.ex:722: Enum.fetch!/2

I don't understand how the statuses (:ok, :error) might be used in application code yet by I'm curious and can't wait to find out!