Either Up or Down.

The other direction. Down ⇆ Up

Save a location alongside a structure.

import Array
import Array.Linear


Array.fromList [ 'a', 'c', 'd' ]
    |> Linear.at ( Down, 2 )
    |> Array.Linear.insert (\() -> 'b')
--> Array.fromList [ 'a', 'b', 'c', 'd' ]

Locating an index can fail for

• negative numbers
• numbers >= the structure's length