Data.Sequence

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

• Ralf Hinze and Ross Paterson, "Finger trees: a simple general-purpose data structure", Journal of Functional Programming 16:2 (2006) pp 197-217. http://www.soi.city.ac.uk/~ross/papers/FingerTree.html

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.

Documentation

data Seq a

General-purpose finite sequences.

Instances

Monad Seq

Functor Seq

Typeable1 Seq

MonadPlus Seq

Foldable Seq

Traversable 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

Foldable ViewL

Traversable 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

Foldable ViewR

Traversable 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.