Data.Utils.List

This module provides various utilities for working with lists.

Documentation

splitLast :: [a] -> Maybe ([a], a)

Splits off the last element of a non-empty list.

>>> splitLast [1, 2, 3]
Just ([1,2],3)

>>> splitLast []
Nothing

pick :: Int -> [a] -> (a, [a])

Given a valid index, returns the list element at the index and the remaining elements.

>>> pick 1 [1,2,3,4]
(2,[1,3,4])

distribute :: Int -> [a] -> [[a]]

Distributes the elements of a list as uniformly as possible amongst a specified number of groups.

>>> distribute 3 [1,2,3,4,5]
[[3],[4,1],[5,2]]

pad :: Int -> a -> [a] -> [a]

Pads a litst with a provided element on the left.

>>> pad 4 'x' "oo"
"xxoo"

data ListEditorT a m b

ListEditorT a m is a monad transformer for editting lists of type [a].

Instances

Monad m => Monad (ListEditorT a m)

Methods

(>>=) :: ListEditorT a m a -> (a -> ListEditorT a m b) -> ListEditorT a m b

(>>) :: ListEditorT a m a -> ListEditorT a m b -> ListEditorT a m b

return :: a -> ListEditorT a m a

fail :: String -> ListEditorT a m a

Functor m => Functor (ListEditorT a m)

Methods

fmap :: (a -> b) -> ListEditorT a m a -> ListEditorT a m b

(<$) :: a -> ListEditorT a m b -> ListEditorT a m a

Monad m => Applicative (ListEditorT a m)

Methods

pure :: a -> ListEditorT a m a

(<*>) :: ListEditorT a m (a -> b) -> ListEditorT a m a -> ListEditorT a m b

(*>) :: ListEditorT a m a -> ListEditorT a m b -> ListEditorT a m b

(<*) :: ListEditorT a m a -> ListEditorT a m b -> ListEditorT a m a

editListT :: Monad m => ListEditorT a m () -> [a] -> m [a]

Runs the editor.

editT :: Monad m => [a] -> ListEditorT a m ()

Replaces the list at the "cursor" with the provided list.

tryLeftT :: Monad m => ListEditorT a m Bool

Tries to move the "cursor" to the left.

tryRightT :: Monad m => ListEditorT a m Bool

Tries to move the "cursor" to the right.

focusT :: Monad m => ListEditorT a m [a]

Gets the list under the "cursor".

type ListEditor a = ListEditorT a Identity

Monad for pure list editting.

editList :: ListEditor a () -> [a] -> [a]

Runs the pure editor.

>>> editList (do _ <- tryRightT; editT [3,2]) [1,2,3]
[1,3,2]

pairs :: [a] -> [(a, a)]

Gets all pairs of adjacent list elements.

>>> pairs "Haskell"
[('H','a'),('a','s'),('s','k'),('k','e'),('e','l'),('l','l')]

indexOf :: Eq a => [a] -> a -> Maybe Int

Gets the first index of the provided element in the list or Nothing if it is not in the list.

>>> indexOf "Haskell" 'l'
Just 5

>>> indexOf "Haskell" 'y'
Nothing

safeHead :: [a] -> Maybe a

Returns the head of a non-empty list or Nothing for the empty list.

>>> safeHead "Haskell"
Just 'H'

>>> safeHead ""
Nothing