Data.Sequence
 Portability portable Stability experimental Maintainer libraries@haskell.org
 Contents Construction Deconstruction Queries Views Indexing Transformations
Description

General purpose finite sequences. Apart from being finite and having strict operations, sequences also differ from lists in supporting a wider variety of operations efficiently.

An amortized running time is given for each operation, with n referring to the length of the sequence and i being the integral index used by some operations. These bounds hold even in a persistent (shared) setting.

The implementation uses 2-3 finger trees annotated with sizes, as described in section 4.2 of

Note: Many of these operations have the same names as similar operations on lists in the Prelude. The ambiguity may be resolved using either qualification or the hiding clause.

Synopsis
data Seq a
empty :: Seq a
singleton :: a -> Seq a
(<|) :: a -> Seq a -> Seq a
(|>) :: Seq a -> a -> Seq a
(><) :: Seq a -> Seq a -> Seq a
fromList :: [a] -> Seq a
null :: Seq a -> Bool
length :: Seq a -> Int
data ViewL a
 = EmptyL | a :< (Seq a)
viewl :: Seq a -> ViewL a
data ViewR a
 = EmptyR | (Seq a) :> a
viewr :: Seq a -> ViewR a
index :: Seq a -> Int -> a
adjust :: (a -> a) -> Int -> Seq a -> Seq a
update :: Int -> a -> Seq a -> Seq a
take :: Int -> Seq a -> Seq a
drop :: Int -> Seq a -> Seq a
splitAt :: Int -> Seq a -> (Seq a, Seq a)
reverse :: Seq a -> Seq a
Documentation
data Seq a
General-purpose finite sequences.
Instances
 Monad Seq Functor Seq Typeable1 Seq MonadPlus Seq Traversable Seq Foldable Seq Eq a => Eq (Seq a) Data a => Data (Seq a) Ord a => Ord (Seq a) Read a => Read (Seq a) Show a => Show (Seq a) Monoid (Seq a)
Construction
empty :: Seq a
O(1). The empty sequence.
singleton :: a -> Seq a
O(1). A singleton sequence.
(<|) :: a -> Seq a -> Seq a
O(1). Add an element to the left end of a sequence. Mnemonic: a triangle with the single element at the pointy end.
(|>) :: Seq a -> a -> Seq a
O(1). Add an element to the right end of a sequence. Mnemonic: a triangle with the single element at the pointy end.
(><) :: Seq a -> Seq a -> Seq a
O(log(min(n1,n2))). Concatenate two sequences.
fromList :: [a] -> Seq a
O(n). Create a sequence from a finite list of elements. There is a function toList in the opposite direction for all instances of the Foldable class, including Seq.
Deconstruction
Additional functions for deconstructing sequences are available via the Foldable instance of Seq.
Queries
null :: Seq a -> Bool
O(1). Is this the empty sequence?
length :: Seq a -> Int
O(1). The number of elements in the sequence.
Views
data ViewL a
View of the left end of a sequence.
Constructors
 EmptyL empty sequence a :< (Seq a) leftmost element and the rest of the sequence
Instances
 Functor ViewL Typeable1 ViewL Traversable ViewL Foldable ViewL Eq a => Eq (ViewL a) Data a => Data (ViewL a) Ord a => Ord (ViewL a) Read a => Read (ViewL a) Show a => Show (ViewL a)
viewl :: Seq a -> ViewL a
O(1). Analyse the left end of a sequence.
data ViewR a
View of the right end of a sequence.
Constructors
 EmptyR empty sequence (Seq a) :> a the sequence minus the rightmost element, and the rightmost element
Instances
 Functor ViewR Typeable1 ViewR Traversable ViewR Foldable ViewR Eq a => Eq (ViewR a) Data a => Data (ViewR a) Ord a => Ord (ViewR a) Read a => Read (ViewR a) Show a => Show (ViewR a)
viewr :: Seq a -> ViewR a
O(1). Analyse the right end of a sequence.
Indexing
index :: Seq a -> Int -> a
O(log(min(i,n-i))). The element at the specified position, which should be a positive integer less than the size of the sequence. If the position is out of range, index fails with an error.
adjust :: (a -> a) -> Int -> Seq a -> Seq a
O(log(min(i,n-i))). Update the element at the specified position. If the position is out of range, the original sequence is returned.
update :: Int -> a -> Seq a -> Seq a
O(log(min(i,n-i))). Replace the element at the specified position. If the position is out of range, the original sequence is returned.
take :: Int -> Seq a -> Seq a
O(log(min(i,n-i))). The first i elements of a sequence. If i is negative, take i s yields the empty sequence. If the sequence contains fewer than i elements, the whole sequence is returned.
drop :: Int -> Seq a -> Seq a
O(log(min(i,n-i))). Elements of a sequence after the first i. If i is negative, take i s yields the whole sequence. If the sequence contains fewer than i elements, the empty sequence is returned.
splitAt :: Int -> Seq a -> (Seq a, Seq a)
O(log(min(i,n-i))). Split a sequence at a given position. splitAt i s = (take i s, drop i s).
Transformations
reverse :: Seq a -> Seq a
O(n). The reverse of a sequence.