pointedlist-0.1: A zipper-like comonad which works as a list, tracking a position.

Data.List.PointedList

Description

An implementation of a zipper-like non-empty list structure that tracks an index position in the list (the focus).

Synopsis

Documentation

data PointedList a Source

The implementation of the pointed list structure which tracks the current position in the list structure.

Constructors

PointedList [a] a [a] 

Instances

singleton :: a -> PointedList aSource

Create a PointedList with a single element.

fromList :: [a] -> Maybe (PointedList a)Source

Possibly create a Just PointedList if the provided list has at least one element; otherwise, return Nothing.

The provided list's head will be the focus of the list, and the rest of list will follow on the right side.

fromListEnd :: [a] -> Maybe (PointedList a)Source

Possibly create a Just PointedList if the provided list has at least one element; otherwise, return Nothing.

The provided list's last element will be the focus of the list, following the rest of the list in order, to the left.

focus :: PointedList a -> aSource

The focus element of the pointed list.

next :: PointedList a -> Maybe (PointedList a)Source

Possibly move the focus to the next element in the list.

tryNext :: PointedList a -> PointedList aSource

Attempt to move the focus to the next element, or error if there are no more elements.

previous :: PointedList a -> Maybe (PointedList a)Source

Possibly move the focus to the previous element in the list.

tryPrevious :: PointedList a -> PointedList aSource

Attempt to move the focus to the previous element, or error if there are no more elements.

insert :: a -> PointedList a -> PointedList aSource

An alias for insertRight.

insertLeft :: a -> PointedList a -> PointedList aSource

Insert an element to the left of the focus, then move the focus to the new element.

insertRight :: a -> PointedList a -> PointedList aSource

Insert an element to the right of the focus, then move the focus to the new element.

delete :: PointedList a -> Maybe (PointedList a)Source

An alias of deleteRight.

deleteLeft :: PointedList a -> Maybe (PointedList a)Source

Possibly delete the element at the focus, then move the element on the left to the focus. If no element is on the left, focus on the element to the right. If the deletion will cause the list to be empty, return Nothing.

deleteRight :: PointedList a -> Maybe (PointedList a)Source

Possibly delete the element at the focus, then move the element on the right to the focus. If no element is on the right, focus on the element to the left. If the deletion will cause the list to be empty, return Nothing.

length :: PointedList a -> IntSource

The length of the list.

atStart :: PointedList a -> BoolSource

Whether the focus is the first element.

atEnd :: PointedList a -> BoolSource

Whether the focus is the last element.

positions :: PointedList a -> PointedList (PointedList a)Source

Create a PointedList of variations of the provided PointedList, in which each element is focused, with the provided PointedList as the focus of the sets.

contextMap :: (PointedList a -> b) -> PointedList a -> PointedList bSource

Map over the PointedLists created via positions, such that f is called with each element of the list focused in the provided PointedList. An example makes this easier to understand: 

 contextMap atStart (fromJust $ fromList [1..5])