# :: Ord a => [a] -> [a]

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

>>> take 20 \$ cycle [42]
[42,42,42,42,42,42,42,42,42,42...

>>> take 20 \$ cycle [2, 5, 7]
[2,5,7,2,5,7,2,5,7,2,5,7...
```
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
```