# Data.List

- Package
- purescript-lists
- Repository
- purescript/purescript-lists

This module defines a type of *strict* linked lists, and associated helper
functions and type class instances.

*Note*: Depending on your use-case, you may prefer to use
`Data.Sequence`

instead, which might give better performance for certain
use cases. This module is an improvement over `Data.Array`

when working with
immutable lists of data in a purely-functional setting, but does not have
good random-access performance.

### #toUnfoldable Source

`toUnfoldable :: forall f. Unfoldable f => List ~> f`

Convert a list into any unfoldable structure.

Running time: `O(n)`

### #fromFoldable Source

`fromFoldable :: forall f. Foldable f => f ~> List`

Construct a list from a foldable structure.

Running time: `O(n)`

### #(..) Source

Operator alias for Data.List.range *(non-associative / precedence 8)*

An infix synonym for `range`

.

### #some Source

`some :: forall a f. Alternative f => Lazy (f (List a)) => f a -> f (List a)`

Attempt a computation multiple times, requiring at least one success.

The `Lazy`

constraint is used to generate the result lazily, to ensure
termination.

### #someRec Source

`someRec :: forall a f. MonadRec f => Alternative f => f a -> f (List a)`

A stack-safe version of `some`

, at the cost of a `MonadRec`

constraint.

### #many Source

`many :: forall a f. Alternative f => Lazy (f (List a)) => f a -> f (List a)`

Attempt a computation multiple times, returning as many successful results as possible (possibly zero).

The `Lazy`

constraint is used to generate the result lazily, to ensure
termination.

### #manyRec Source

`manyRec :: forall a f. MonadRec f => Alternative f => f a -> f (List a)`

A stack-safe version of `many`

, at the cost of a `MonadRec`

constraint.

### #(!!) Source

Operator alias for Data.List.index *(left-associative / precedence 8)*

An infix synonym for `index`

.

### #elemLastIndex Source

`elemLastIndex :: forall a. Eq a => a -> List a -> Maybe Int`

Find the index of the last element equal to the specified element.

### #findLastIndex Source

`findLastIndex :: forall a. (a -> Boolean) -> List a -> Maybe Int`

Find the last index for which a predicate holds.

### #mapWithIndex Source

`mapWithIndex :: forall b a. (Int -> a -> b) -> List a -> List b`

Apply a function to each element and its index in a list starting at 0.

Deprecated. Use Data.FunctorWithIndex instead.

### #stripPrefix Source

`stripPrefix :: forall a. Eq a => Pattern a -> List a -> Maybe (List a)`

If the list starts with the given prefix, return the portion of the list left after removing it, as a Just value. Otherwise, return Nothing.

`stripPrefix (Pattern (1:Nil)) (1:2:Nil) == Just (2:Nil)`

`stripPrefix (Pattern Nil) (1:Nil) == Just (1:Nil)`

`stripPrefix (Pattern (2:Nil)) (1:Nil) == Nothing`

Running time: `O(n)`

where `n`

is the number of elements to strip.

### #span Source

`span :: forall a. (a -> Boolean) -> List a -> { init :: List a, rest :: List a }`

Split a list into two parts:

- the longest initial segment for which all elements satisfy the specified predicate
- the remaining elements

For example,

```
span (\n -> n % 2 == 1) (1 : 3 : 2 : 4 : 5 : Nil) == { init: (1 : 3 : Nil), rest: (2 : 4 : 5 : Nil) }
```

Running time: `O(n)`

### #group Source

`group :: forall a. Eq a => List a -> List (NonEmptyList a)`

Group equal, consecutive elements of a list into lists.

For example,

```
group (1 : 1 : 2 : 2 : 1 : Nil) == (1 : 1 : Nil) : (2 : 2 : Nil) : (1 : Nil) : Nil
```

Running time: `O(n)`

### #group' Source

`group' :: forall a. Ord a => List a -> List (NonEmptyList a)`

Sort and then group the elements of a list into lists.

```
group' [1,1,2,2,1] == [[1,1,1],[2,2]]
```

### #groupBy Source

`groupBy :: forall a. (a -> a -> Boolean) -> List a -> List (NonEmptyList a)`

Group equal, consecutive elements of a list into lists, using the specified equivalence relation to determine equality.

Running time: `O(n)`

### #difference Source

`difference :: forall a. Eq a => List a -> List a -> List a`

Delete the first occurrence of each element in the second list from the first list.

Running time: `O(n^2)`

### #intersectBy Source

`intersectBy :: forall a. (a -> a -> Boolean) -> List a -> List a -> List a`

Calculate the intersection of two lists, using the specified function to determine equality of elements.

Running time: `O(n^2)`

### #zipWith Source

`zipWith :: forall c b a. (a -> b -> c) -> List a -> List b -> List c`

Apply a function to pairs of elements at the same positions in two lists, collecting the results in a new list.

If one list is longer, elements will be discarded from the longer list.

For example

```
zipWith (*) (1 : 2 : 3 : Nil) (4 : 5 : 6 : 7 Nil) == 4 : 10 : 18 : Nil
```

Running time: `O(min(m, n))`

### #zipWithA Source

`zipWithA :: forall c b a m. Applicative m => (a -> b -> m c) -> List a -> List b -> m (List c)`

A generalization of `zipWith`

which accumulates results in some `Applicative`

functor.

### #transpose Source

`transpose :: forall a. List (List a) -> List (List a)`

The 'transpose' function transposes the rows and columns of its argument. For example,

```
transpose ((1:2:3:Nil) : (4:5:6:Nil) : Nil) ==
((1:4:Nil) : (2:5:Nil) : (3:6:Nil) : Nil)
```

If some of the rows are shorter than the following rows, their elements are skipped:

```
transpose ((10:11:Nil) : (20:Nil) : Nil : (30:31:32:Nil) : Nil) ==
((10:20:30:Nil) : (11:31:Nil) : (32:Nil) : Nil)
```

## Re-exports from **Data.**Foldable

### #intercalate Source

`intercalate :: forall m f. Foldable f => Monoid m => m -> f m -> m`

Fold a data structure, accumulating values in some `Monoid`

,
combining adjacent elements using the specified separator.

For example:

```
> intercalate ", " ["Lorem", "ipsum", "dolor"]
= "Lorem, ipsum, dolor"
> intercalate "*" ["a", "b", "c"]
= "a*b*c"
> intercalate [1] [[2, 3], [4, 5], [6, 7]]
= [2, 3, 1, 4, 5, 1, 6, 7]
```

### #any Source

`any :: forall f b a. Foldable f => HeytingAlgebra b => (a -> b) -> f a -> b`

`any f`

is the same as `or <<< map f`

; map a function over the structure,
and then get the disjunction of the results.

### #all Source

`all :: forall f b a. Foldable f => HeytingAlgebra b => (a -> b) -> f a -> b`

`all f`

is the same as `and <<< map f`

; map a function over the structure,
and then get the conjunction of the results.

## Re-exports from **Data.**List.Types

### #List Source

`data List a`

#### Constructors

#### Instances

`(Show a) => Show (List a)`

`(Eq a) => Eq (List a)`

`Eq1 List`

`(Ord a) => Ord (List a)`

`Ord1 List`

`Semigroup (List a)`

`Monoid (List a)`

`Functor List`

`FunctorWithIndex Int List`

`Foldable List`

`FoldableWithIndex Int List`

`Unfoldable1 List`

`Unfoldable List`

`Traversable List`

`TraversableWithIndex Int List`

`Apply List`

`Applicative List`

`Bind List`

`Monad List`

`Alt List`

`Plus List`

`Alternative List`

`MonadZero List`

`MonadPlus List`

`Extend List`

## Re-exports from **Data.**Traversable

### #scanr Source

`scanr :: forall f b a. Traversable f => (a -> b -> b) -> b -> f a -> f b`

Fold a data structure from the right, keeping all intermediate results
instead of only the final result. Note that the initial value does not
appear in the result (unlike Haskell's `Prelude.scanr`

).

```
scanr (+) 0 [1,2,3] = [6,5,3]
scanr (flip (-)) 10 [1,2,3] = [4,5,7]
```

### #scanl Source

`scanl :: forall f b a. Traversable f => (b -> a -> b) -> b -> f a -> f b`

Fold a data structure from the left, keeping all intermediate results
instead of only the final result. Note that the initial value does not
appear in the result (unlike Haskell's `Prelude.scanl`

).

```
scanl (+) 0 [1,2,3] = [1,3,6]
scanl (-) 10 [1,2,3] = [9,7,4]
```