:: Ord a => [a] -> [a] -package:ghc -package:safe -package:errors -package:Cabal -package:containers

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. The argument must be finite.

Examples

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

>>> sort "haskell"
"aehklls"

>>> import Data.Semigroup(Arg(..))

>>> sort [Arg ":)" 0, Arg ":D" 0, Arg ":)" 1, Arg ":3" 0, Arg ":D" 1]
[Arg ":)" 0,Arg ":)" 1,Arg ":3" 0,Arg ":D" 0,Arg ":D" 1]

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.

Examples

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

>>> take 10 (cycle [42])
[42,42,42,42,42,42,42,42,42,42]

>>> take 10 (cycle [2, 5, 7])
[2,5,7,2,5,7,2,5,7,2]

>>> take 1 (cycle (42 : undefined))
[42]

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

Laziness

reverse is lazy in its elements.

>>> head (reverse [undefined, 1])
1

>>> reverse (1 : 2 : undefined)
*** Exception: Prelude.undefined

Examples

>>> 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.

Warning: This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty.

Return all the elements of a list except the last one. The list must be non-empty. WARNING: This function is partial. Consider using unsnoc instead.

Examples

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

>>> init [1]
[]

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

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

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

Examples

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

>>> tail [1]
[]

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

Sort a vector.

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]

Generalized version of runInBoundThread.

Generalized version of runInUnboundThread.

Generalized version of mask_.

Generalized version of uninterruptibleMask_.

A trivial product type that stores nothing and simply returns the given tag as the result.