Module

Data.List.Lazy

Package
purescript-lists
Repository
purescript/purescript-lists

This module defines a type of lazy 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)

#singleton Source

singleton :: forall a. a -> List a

Create a list with a single element.

Running time: O(1)

#(..) Source

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

An infix synonym for range.

#range Source

range :: Int -> Int -> List Int

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

#replicate Source

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

Create a list with repeated instances of a value.

#replicateM Source

replicateM :: forall m a. Monad m => Int -> m a -> m (List a)

Perform a monadic action n times collecting all of the results.

#some Source

some :: forall f a. 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.

#many Source

many :: forall f a. 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.

#repeat Source

repeat :: forall a. a -> List a

Create a list by repeating an element

#iterate Source

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

Create a list by iterating a function

#cycle Source

cycle :: forall a. List a -> List a

Create a list by repeating another list

#null Source

null :: forall a. List a -> Boolean

Test whether a list is empty.

Running time: O(1)

#length Source

length :: forall a. List a -> Int

Get the length of a list

Running time: O(n)

#snoc Source

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 Source

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

Insert an element into a sorted list.

Running time: O(n)

#insertBy Source

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 Source

head :: List ~> Maybe

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

Running time: O(1).

#last Source

last :: List ~> Maybe

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

Running time: O(n).

#tail Source

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 Source

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 Source

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)

#(!!) Source

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

An infix synonym for index.

#index Source

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.

#elemIndex Source

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

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

#elemLastIndex Source

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

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

#findIndex Source

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

Find the first index for which a predicate holds.

#findLastIndex Source

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

Find the last index for which a predicate holds.

#insertAt Source

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

This function differs from the strict equivalent in that out-of-bounds arguments result in the element being appended at the end of the list.

Running time: O(n)

#deleteAt Source

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

This function differs from the strict equivalent in that out-of-bounds arguments result in the original list being returned unchanged.

Running time: O(n)

#updateAt Source

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

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

This function differs from the strict equivalent in that out-of-bounds arguments result in the original list being returned unchanged.

Running time: O(n)

#modifyAt Source

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

This function differs from the strict equivalent in that out-of-bounds arguments result in the original list being returned unchanged.

Running time: O(n)

#alterAt Source

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

This function differs from the strict equivalent in that out-of-bounds arguments result in the original list being returned unchanged.

Running time: O(n)

#reverse Source

reverse :: List ~> List

Reverse a list.

Running time: O(n)

#concat Source

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 Source

concatMap :: forall a b. (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 Source

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 Source

filterM :: forall a m. 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 Source

mapMaybe :: forall a b. (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 Source

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

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

#Pattern Source

newtype Pattern a

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

Constructors

Instances

#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 (fromFoldable [1])) (fromFoldable [1,2]) == Just (fromFoldable [2])
  • stripPrefix (Pattern (fromFoldable [])) (fromFoldable [1]) == Just (fromFoldable [1])
  • stripPrefix (Pattern (fromFoldable [2])) (fromFoldable [1]) == Nothing

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

#slice Source

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

Extract a sublist by a start and end index.

#take Source

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 Source

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 Source

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 Source

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 Source

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) == Tuple (1 : 3 : Nil) (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)

#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)

#partition Source

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

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

Running time: O(n)

#nub Source

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

Remove duplicate elements from a list.

Running time: O(n^2)

#nubBy Source

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 Source

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

Calculate the union of two lists.

Running time: O(n^2)

#unionBy Source

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 Source

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 Source

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)

#(\\) Source

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

#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)

#intersect Source

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

Calculate the intersection of two lists.

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 a b c. (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 m a b c. 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 Source

zip :: forall a b. 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 Source

unzip :: forall a b. 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 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)

#foldM Source

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

Perform a fold using a monadic step function.

#foldrLazy Source

foldrLazy :: forall a b. Lazy b => (a -> b -> b) -> b -> List a -> b

Perform a right fold lazily

#scanrLazy Source

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

Perform a right scan lazily

Re-exports from Data.Foldable

#foldMap Source

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

#foldl Source

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

#foldr Source

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

#notElem Source

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

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

#intercalate Source

intercalate :: forall f m. 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]

#fold Source

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

Fold a data structure, accumulating values in some Monoid.

#findMap Source

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

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

#find Source

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

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

#elem Source

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

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

#any Source

any :: forall a b f. 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 a b f. 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.Lazy.Types

#Step Source

data Step a

A list is either empty (represented by the Nil constructor) or non-empty, in which case it consists of a head element, and another list (represented by the Cons constructor).

Constructors

#step Source

step :: forall a. List a -> Step a

Unwrap a lazy linked list

#nil Source

nil :: forall a. List a

The empty list.

Running time: O(1)

#cons Source

cons :: forall a. a -> List a -> List a

Attach an element to the front of a lazy list.

Running time: O(1)

#(:) Source

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

An infix alias for cons; attaches an element to the front of a list.

Running time: O(1)

Re-exports from Data.Traversable

#scanr Source

scanr :: forall a b f. 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 a b f. 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]