A Zipper a is a nonempty list with a focused element.

Add elements at the end of the Zipper.

import Zipper exposing (Zipper(..))


Zipper.append [ 5, 4 ] (Zipper [ 0 ] 1 [ 2, 3 ]) == Zipper [ 0 ] 1 [ 2, 3, 5, 4 ]

Add elements at the beginning of the Zipper.

import Zipper exposing (Zipper(..))


Zipper.prepend [ -1, -2 ] (Zipper [ 0 ] 1 [ 2, 3 ]) == Zipper [ -1, -2, 0 ] 1 [ 2, 3 ]

Transforms a Zipper into a regular list.

import Zipper exposing (Zipper(..))


Zipper.toList (Zipper [0] 1 [2,3,4]) == [0,1,2,3,4]

Returns the elements before the focused element.

  import Zipper exposing (Zipper(..))


  Zipper.prev (Zipper [0] 1 [2,3,4]) == [0]

Returns the focused element.

import Zipper exposing (Zipper(..))


Zipper.extract (Zipper [0] 1 [2,3,4]) == 1

Returns the elements after the focused element.

  import Zipper exposing (Zipper(..))


  Zipper.next (Zipper [0] 1 [2,3,4]) == [2,3,4]

Attempts to select the element to the left of the focus, returns Nothing if there are no previous elements.

  import Zipper exposing (Zipper(..))


  Zipper.leftMay (Zipper [] 1 [2,3,4]) == Nothing


  Zipper.leftMay (Zipper [1] 2 [3,4]) == Just (Zipper [] 1 [2, 3, 4])

Attempts to select the element to the right of the focus, returns Nothing if there are no next elements.

import Zipper exposing (Zipper(..))


Zipper.rightMay (Zipper [0] 1 []) == Nothing


Zipper.rightMay (Zipper [1] 2 [3,4]) == Just (Zipper [1, 2] 3 [4])

Attempts to select the element to the left of the focus. Returns the Zipper unchanged if there are no previous elements.

  import Zipper exposing (Zipper(..))


  Zipper.left (Zipper [] 1 [2,3,4]) == Zipper [] 1 [2,3,4]


  Zipper.left (Zipper [1] 2 [3,4]) == Zipper [] 1 [2, 3, 4]

Attempts to select the element to the right of the focus. Returns the Zipper unchanged if there are no next elements.

import Zipper exposing (Zipper(..))


Zipper.right (Zipper [0] 1 []) == Zipper [0] 1 []


Zipper.right (Zipper [1] 2 [3,4]) == Zipper [1, 2] 3 [4]

Apply a function to every element in the Zipper.

import Zipper exposing (Zipper(..))


Zipper.map (\x -> 2 * x) (Zipper [2, 0, 5] 1 [2]) == Zipper [4, 0, 10] 2 [4]

Returns a Zipper in which every element is a Zipper list.

import Zipper exposing (Zipper(..))


duplicate (Zipper [0] 1 [2]) == Zipper [Zipper [] 0 [1,2]] (Zipper [0] 1 [2]) [Zipper [0, 1] 2 []]

Map elements in the Zipper, having access to the elements before and after it.

import Zipper exposing (Zipper(..))


maxSoFar (Zipper prev curr _) = List.foldr Basics.max curr prev


Zipper.extend maxSoFar (Zipper [2, 1, 3, 4, 5] 1 [2]) == Zipper [2, 2, 3, 4, 5] 5 [5]