:: Ord a => [a] -> [a] is:exact -package:imports -package:incipit-base -package:base-prelude -package:Cabal-syntax -package:integration -package:base -package:mono-traversable -package:containers

Remove duplicates but keep elements in order. O(n * log n)

Like nub, but has O(n log n) complexity instead of O(n^2). Code for ordNub and listUnion taken from Niklas Hambüchen's ordnub package.

A right-biased version of ordNub. Example:

>>> ordNub [1,2,1] :: [Int]
[1,2]

>>> ordNubRight [1,2,1] :: [Int]
[2,1]

O(n log n). The nubOrd function removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element. Unlike the standard nub operator, this version requires an Ord instance and consequently runs asymptotically faster.

nubOrd "this is a test" == "this ae"
nubOrd (take 4 ("this" ++ undefined)) == "this"
\xs -> nubOrd xs == nub xs

O(n log n). The nubSort function sorts and removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element.

nubSort "this is a test" == " aehist"
\xs -> nubSort xs == nub (sort xs)

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 *

A total variant of tail.

A total variant of init.

tailSafe [] = []
tailSafe [1,3,4] = [3,4]

Equivalent to drop 1, but likely to be faster and a single lexeme.

drop1 ""         == ""
drop1 "test"     == "est"
\xs -> drop 1 xs == drop1 xs

Equivalent to dropEnd 1, but likely to be faster and a single lexeme.

dropEnd1 ""         == ""
dropEnd1 "test"     == "tes"
\xs -> dropEnd 1 xs == dropEnd1 xs

Identical to tail, namely that fails on an empty list. Useful to avoid the x-partial warning introduced in GHC 9.8.

tailErr [] = error "Prelude.tail: empty list"
tailErr [1,2,3] = [2,3]

The nub function which removes duplicate elements from a vector.

Sort 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]

A minimum that fails using mzero

A maximum that fails using mzero

Generalized version of runInBoundThread.