Data.List

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

Convert a list into any unfoldable structure.

Running time: O(n)

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

Construct a list from a foldable structure.

Running time: O(n)

singleton :: forall a. a -> List a

Create a list with a single element.

Running time: O(1)

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

An infix synonym for range.

range :: Int -> Int -> List Int

Create a list containing a range of integers, including both endpoints.

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 :: 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 :: 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 :: 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.

null :: forall a. List a -> Boolean

Test whether a list is empty.

Running time: O(1)

length :: forall a. List a -> Int

Get the length of a list

Running time: O(n)

snoc :: forall a. List a -> a -> List a

Append an element to the end of a list, creating a new list.

Running time: O(n)

insert :: forall a. Ord a => a -> List a -> List a

Insert an element into a sorted list.

Running time: O(n)

insertBy :: forall a. (a -> a -> Ordering) -> a -> List a -> List a

Insert an element into a sorted list, using the specified function to determine the ordering of elements.

Running time: O(n)

head :: List ~> Maybe

Get the first element in a list, or Nothing if the list is empty.

Running time: O(1).

last :: List ~> Maybe

Get the last element in a list, or Nothing if the list is empty.

Running time: O(n).

tail :: forall a. List a -> Maybe (List a)

Get all but the first element of a list, or Nothing if the list is empty.

Running time: O(1)

init :: forall a. List a -> Maybe (List a)

Get all but the last element of a list, or Nothing if the list is empty.

Running time: O(n)

uncons :: forall a. List a -> Maybe { head :: a, tail :: List a }

Break a list into its first element, and the remaining elements, or Nothing if the list is empty.

Running time: O(1)

unsnoc :: forall a. List a -> Maybe { init :: List a, last :: a }

Break a list into its last element, and the preceding elements, or Nothing if the list is empty.

Running time: O(n)

index :: forall a. List a -> Int -> Maybe a

Get the element at the specified index, or Nothing if the index is out-of-bounds.

Running time: O(n) where n is the required index.

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

An infix synonym for index.

elemIndex :: forall a. Eq a => a -> List a -> Maybe Int

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

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

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

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

Find the first index for which a predicate holds.

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

Find the last index for which a predicate holds.

insertAt :: forall a. Int -> a -> List a -> Maybe (List a)

Insert an element into a list at the specified index, returning a new list or Nothing if the index is out-of-bounds.

Running time: O(n)

deleteAt :: forall a. Int -> List a -> Maybe (List a)

Delete an element from a list at the specified index, returning a new list or Nothing if the index is out-of-bounds.

Running time: O(n)

updateAt :: forall a. Int -> a -> List a -> Maybe (List a)

Update the element at the specified index, returning a new list or Nothing if the index is out-of-bounds.

Running time: O(n)

modifyAt :: forall a. Int -> (a -> a) -> List a -> Maybe (List a)

Update the element at the specified index by applying a function to the current value, returning a new list or Nothing if the index is out-of-bounds.

Running time: O(n)

alterAt :: forall a. Int -> (a -> Maybe a) -> List a -> Maybe (List a)

Update or delete the element at the specified index by applying a function to the current value, returning a new list or Nothing if the index is out-of-bounds.

Running time: O(n)

reverse :: List ~> List

Reverse a list.

Running time: O(n)

concat :: forall a. List (List a) -> List a

Flatten a list of lists.

Running time: O(n), where n is the total number of elements.

concatMap :: forall b a. (a -> List b) -> List a -> List b

Apply a function to each element in a list, and flatten the results into a single, new list.

Running time: O(n), where n is the total number of elements.

filter :: forall a. (a -> Boolean) -> List a -> List a

Filter a list, keeping the elements which satisfy a predicate function.

Running time: O(n)

filterM :: forall m a. Monad m => (a -> m Boolean) -> List a -> m (List a)

Filter where the predicate returns a monadic Boolean.

For example:

powerSet :: forall a. [a] -> [[a]]
powerSet = filterM (const [true, false])

mapMaybe :: forall b a. (a -> Maybe b) -> List a -> List b

Apply a function to each element in a list, keeping only the results which contain a value.

Running time: O(n)

catMaybes :: forall a. List (Maybe a) -> List a

Filter a list of optional values, keeping only the elements which contain a value.

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.

sort :: forall a. Ord a => List a -> List a

Sort the elements of an list in increasing order.

sortBy :: forall a. (a -> a -> Ordering) -> List a -> List a

Sort the elements of a list in increasing order, where elements are compared using the specified ordering.

newtype Pattern a

A newtype used in cases where there is a list to be matched.

Constructors

• Pattern (List a)

Instances

• (Eq a) => Eq (Pattern a)
• (Ord a) => Ord (Pattern a)
• Newtype (Pattern a) _
• (Show a) => Show (Pattern a)

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.

slice :: Int -> Int -> List ~> List

Extract a sublist by a start and end index.

take :: forall a. Int -> List a -> List a

Take the specified number of elements from the front of a list.

Running time: O(n) where n is the number of elements to take.

takeWhile :: forall a. (a -> Boolean) -> List a -> List a

Take those elements from the front of a list which match a predicate.

Running time (worst case): O(n)

drop :: forall a. Int -> List a -> List a

Drop the specified number of elements from the front of a list.

Running time: O(n) where n is the number of elements to drop.

dropWhile :: forall a. (a -> Boolean) -> List a -> List a

Drop those elements from the front of a list which match a predicate.

Running time (worst case): O(n)

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

Split a list into two parts:

1. the longest initial segment for which all elements satisfy the specified predicate
2. 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 :: 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' :: 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 :: 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)

partition :: forall a. (a -> Boolean) -> List a -> { no :: List a, yes :: List a }

Returns a lists of elements which do and do not satisfy a predicate.

Running time: O(n)

nub :: forall a. Eq a => List a -> List a

Remove duplicate elements from a list.

Running time: O(n^2)

nubBy :: forall a. (a -> a -> Boolean) -> List a -> List a

Remove duplicate elements from a list, using the specified function to determine equality of elements.

Running time: O(n^2)

union :: forall a. Eq a => List a -> List a -> List a

Calculate the union of two lists.

Running time: O(n^2)

unionBy :: forall a. (a -> a -> Boolean) -> List a -> List a -> List a

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

Running time: O(n^2)

delete :: forall a. Eq a => a -> List a -> List a

Delete the first occurrence of an element from a list.

Running time: O(n)

deleteBy :: forall a. (a -> a -> Boolean) -> a -> List a -> List a

Delete the first occurrence of an element from a list, using the specified function to determine equality of elements.

Running time: O(n)

Operator alias for Data.List.difference (non-associative / precedence 5)

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)

intersect :: forall a. Eq a => List a -> List a -> List a

Calculate the intersection of two lists.

Running time: O(n^2)

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 :: 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 :: 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.

zip :: forall b a. List a -> List b -> List (Tuple a b)

Collect pairs of elements at the same positions in two lists.

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

unzip :: forall b a. List (Tuple a b) -> Tuple (List a) (List b)

Transforms a list of pairs into a list of first components and a list of second components.

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)

foldM :: forall b a m. Monad m => (a -> b -> m a) -> a -> List b -> m a

Perform a fold using a monadic step function.

foldMap :: forall f m a. Foldable f => Monoid m => (a -> m) -> f a -> m

foldl :: forall f b a. Foldable f => (b -> a -> b) -> b -> f a -> b

foldr :: forall f b a. Foldable f => (a -> b -> b) -> b -> f a -> b

notElem :: forall f a. Foldable f => Eq a => a -> f a -> Boolean

Test whether a value is not an element of a data structure.

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.

fold :: forall m f. Foldable f => Monoid m => f m -> m

Fold a data structure, accumulating values in some Monoid.

findMap :: forall f b a. Foldable f => (a -> Maybe b) -> f a -> Maybe b

Try to find an element in a data structure which satisfies a predicate mapping.

find :: forall f a. Foldable f => (a -> Boolean) -> f a -> Maybe a

Try to find an element in a data structure which satisfies a predicate.

elem :: forall f a. Foldable f => Eq a => a -> f a -> Boolean

Test whether a value is an element of a data structure.

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 :: 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.

data List a

Constructors

• Nil
• Cons a (List a)

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
• Foldable List
• Unfoldable List
• Traversable List
• Apply List
• Applicative List
• Bind List
• Monad List
• Alt List
• Plus List
• Alternative List
• MonadZero List
• MonadPlus List
• Extend List

Operator alias for Data.List.Types.Cons (right-associative / precedence 6)

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

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]