:: Ord a => [a] -> [a] -package:html-entities -package:Cabal -package:mono-traversable -package:base is:exact -package:ghc -package:statistics -package:basement -package:incipit-base -package:extra -package:lifted-base -package:errors -package:Cabal-syntax -package:hedgehog -package:vector -package:safe

The sort function implements a stable sorting algorithm. It is a special case of sortBy, which allows the programmer to supply their own comparison function. Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.

>>> sort [1,6,4,3,2,5]
[1,2,3,4,5,6]

The argument must be finite.

The nubOrd function removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element. By using a Set internally it has better asymptotics than the standard nub function.

Strictness

nubOrd is strict in the elements of the list.

Efficiency note

When applicable, it is almost always better to use nubInt or nubIntOn instead of this function, although it can be a little worse in certain pathological cases. For example, to nub a list of characters, use

nubIntOn fromEnum xs

The nub function which removes duplicate elements from a vector.

Removes duplicate elements from a list, keeping only the first occurrence. This is asymptotically faster than using nub from Data.List.

>>> ordNub [3,2,1,3,2,1]
[3,2,1]

cycle ties a finite list into a circular one, or equivalently, the infinite repetition of the original list. It is the identity on infinite lists.

>>> cycle []
*** Exception: Prelude.cycle: empty list

>>> cycle [42]
[42,42,42,42,42,42,42,42,42,42...

>>> cycle [2, 5, 7]
[2,5,7,2,5,7,2,5,7,2,5,7...

Extract the elements after the head of a list, which must be non-empty.

>>> tail [1, 2, 3]
[2,3]

>>> tail [1]
[]

>>> tail []
*** Exception: Prelude.tail: empty list

WARNING: This function is partial. You can use case-matching or uncons instead.

Return all the elements of a list except the last one. The list must be non-empty.

>>> init [1, 2, 3]
[1,2]

>>> init [1]
[]

>>> init []
*** Exception: Prelude.init: empty list

WARNING: This function is partial. You can use reverse with case-matching or uncons instead.

reverse xs returns the elements of xs in reverse order. xs must be finite.

>>> reverse []
[]

>>> reverse [42]
[42]

>>> reverse [2,5,7]
[7,5,2]

>>> reverse [1..]
* Hangs forever *

all nodes of a tree

Take a parser that may consume input, and on failure, go back to where we started and fail as if we didn't consume input.