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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02

Modulepqueue-1.7.0.0Haskell2010

Data.PQueue.Max

General purpose priority queue, supporting view-maximum operations.

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

This implementation is based on a binomial heap augmented with a global root.

This implementation does not guarantee stable behavior.

This implementation offers a number of methods of the form xxxU, where U stands for unordered. No guarantees whatsoever are made on the execution or traversal order of these functions.

Contents

Basic operations
Query operations
Construction operations
Subsets
Extracting subsets
Predicates
Filter/Map
Fold/Functor/Traversable variations
List operations
Unordered operations
Miscellaneous operations

Synopsis

Packagepqueue-1.7.0.0
Exports47
LanguageHaskell2010
LicenceBSD-3-Clause
SourceMax.hs

newtypenewtype MaxQueue a

A priority queue with elements of type a. Supports extracting the maximum element. Implemented as a wrapper around MinQueue.

Instances8Eq, Data, Ord, Read, Show, Semigroup, …

Ord a => Eq (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
(Data a, Ord a) => Data (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
Ord a => Ord (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
(Ord a, Read a) => Read (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
(Ord a, Show a) => Show (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
Ord a => Semigroup (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
Ord a => Monoid (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max
NFData a => NFData (MaxQueue a)Defined in pqueue-1.7.0.0 · Data.PQueue.Max

Basic operations

valueempty :: MaxQueue a

O(1). The empty priority queue.

valuenull :: MaxQueue a -> Bool

O(1). Is this the empty priority queue?

valuesize :: MaxQueue a -> Int

O(1). The number of elements in the queue.

Query operations

valuefindMax :: MaxQueue a -> a

O(1). Returns the maximum element of the queue. Throws an error on an empty queue.

valuegetMax :: MaxQueue a -> Maybe a

O(1). The top (maximum) element of the queue, if there is one.

valuedeleteMax :: Ord a => MaxQueue a -> MaxQueue a

O(\log n). Deletes the maximum element of the queue. Does nothing on an empty queue.

valuedeleteFindMax :: Ord a => MaxQueue a -> (a, MaxQueue a)

O(\log n). Extracts the maximum element of the queue. Throws an error on an empty queue.

valuedelete :: Ord a => MaxQueue a -> Maybe (MaxQueue a)

O(\log n). Delete the top (maximum) element of the sequence, if there is one.

valuemaxView :: Ord a => MaxQueue a -> Maybe (a, MaxQueue a)

O(\log n). Extract the top (maximum) element of the sequence, if there is one.

Construction operations

valuesingleton :: a -> MaxQueue a

O(1). Construct a priority queue with a single element.

valueinsert :: Ord a => a -> MaxQueue a -> MaxQueue a

O(1). Insert an element into the priority queue.

valueunion :: Ord a => MaxQueue a -> MaxQueue a -> MaxQueue a

O(\log min(n_1,n_2)). Take the union of two priority queues.

valueunions :: Ord a => [MaxQueue a] -> MaxQueue a

Takes the union of a list of priority queues. Equivalent to foldl union empty.

Subsets

Extracting subsets

value(!!) :: Ord a => MaxQueue a -> Int -> a

O(k \log n). Returns the (k+1)th largest element of the queue.

valuetake :: Ord a => Int -> MaxQueue a -> [a]

O(k \log n). Returns the list of the k largest elements of the queue, in descending order, or all elements of the queue, if k >= n.

valuedrop :: Ord a => Int -> MaxQueue a -> MaxQueue a

O(k \log n). Returns the queue with the k largest elements deleted, or the empty queue if k >= n.

valuesplitAt :: Ord a => Int -> MaxQueue a -> ([a], MaxQueue a)

O(k \log n). Equivalent to (take k queue, drop k queue).

Predicates

valuetakeWhile :: Ord a => (a -> Bool) -> MaxQueue a -> [a]

takeWhile, applied to a predicate p and a queue queue, returns the longest prefix (possibly empty) of queue of elements that satisfy p.

valuedropWhile :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a

dropWhile p queue returns the queue remaining after takeWhile p queue.

valuespan :: Ord a => (a -> Bool) -> MaxQueue a -> ([a], MaxQueue a)

span, applied to a predicate p and a queue queue, returns a tuple where first element is longest prefix (possibly empty) of queue of elements that satisfy p and second element is the remainder of the queue.

valuebreak :: Ord a => (a -> Bool) -> MaxQueue a -> ([a], MaxQueue a)

break, applied to a predicate p and a queue queue, returns a tuple where first element is longest prefix (possibly empty) of queue of elements that do not satisfy p and second element is the remainder of the queue.

Filter/Map

valuefilter :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a

O(n). Returns a queue of those elements which satisfy the predicate.

valuepartition :: Ord a => (a -> Bool) -> MaxQueue a -> (MaxQueue a, MaxQueue a)

O(n). Returns a pair of queues, where the left queue contains those elements that satisfy the predicate, and the right queue contains those that do not.

valuemapMaybe :: Ord b => (a -> Maybe b) -> MaxQueue a -> MaxQueue b

O(n). Maps a function over the elements of the queue, and collects the Just values.

valuemapEither

:: (Ord b, Ord c)
=> a -> Either b c
-> MaxQueue a
-> (MaxQueue b, MaxQueue c)

O(n). Maps a function over the elements of the queue, and separates the Left and Right values.

Fold/Functor/Traversable variations

valuemap :: Ord b => (a -> b) -> MaxQueue a -> MaxQueue b

O(n). Creates a new priority queue containing the images of the elements of this queue. Equivalent to fromList . Data.List.map f . toList.

valuemapMonotonic :: (a -> b) -> MaxQueue a -> MaxQueue b

O(n). Assumes that the function it is given is (weakly) monotonic (meaning that x <= y implies f x <= f y), and applies this function to every element of the priority queue, as in fmap. If the function is not monotonic, the result is undefined.

valuefoldrAsc :: Ord a => (a -> b -> b) -> b -> MaxQueue a -> b

O(n \log n). Performs a right-fold on the elements of a priority queue in ascending order. foldrAsc f z q == foldlDesc (flip f) z q.

valuefoldlAsc :: Ord a => (b -> a -> b) -> b -> MaxQueue a -> b

O(n \log n). Performs a left-fold on the elements of a priority queue in descending order. foldlAsc f z q == foldrDesc (flip f) z q.

valuefoldrDesc :: Ord a => (a -> b -> b) -> b -> MaxQueue a -> b

O(n \log n). Performs a right-fold on the elements of a priority queue in descending order.

valuefoldlDesc :: Ord a => (b -> a -> b) -> b -> MaxQueue a -> b

O(n \log n). Performs a left-fold on the elements of a priority queue in descending order.

List operations

valuetoList :: Ord a => MaxQueue a -> [a]

O(n \log n). Returns the elements of the priority queue in descending order. Equivalent to toDescList.

If the order of the elements is irrelevant, consider using toListU.

valuetoAscList :: Ord a => MaxQueue a -> [a]

O(n \log n). Extracts the elements of the priority queue in ascending order.

valuetoDescList :: Ord a => MaxQueue a -> [a]

O(n \log n). Extracts the elements of the priority queue in descending order.

valuefromList :: Ord a => [a] -> MaxQueue a

O(n \log n). Constructs a priority queue from an unordered list.

valuefromAscList :: [a] -> MaxQueue a

O(n). Constructs a priority queue from an ascending list. Warning: Does not check the precondition.

valuefromDescList :: [a] -> MaxQueue a

O(n). Constructs a priority queue from a descending list. Warning: Does not check the precondition.

Unordered operations

valuemapU :: (a -> b) -> MaxQueue a -> MaxQueue b

Deprecated. use mapMonotonic instead

valuefoldrU :: (a -> b -> b) -> b -> MaxQueue a -> b

O(n). Unordered right fold on a priority queue.

valuefoldlU :: (b -> a -> b) -> b -> MaxQueue a -> b

O(n). Unordered left fold on a priority queue. This is rarely what you want; foldrU and foldlU' are more likely to perform well.

valuefoldlU' :: (b -> a -> b) -> b -> MaxQueue a -> b

O(n). Unordered strict left fold on a priority queue.

valuefoldMapU :: Monoid m => (a -> m) -> MaxQueue a -> m

O(n). Unordered monoidal fold on a priority queue.

valueelemsU :: MaxQueue a -> [a]

Equivalent to toListU.

valuetoListU :: MaxQueue a -> [a]

O(n). Returns a list of the elements of the priority queue, in no particular order.

Miscellaneous operations

valuekeysQueue :: MaxPQueue k a -> MaxQueue k

O(n). Constructs a priority queue from the keys of a MaxPQueue.

valueseqSpine :: MaxQueue a -> b -> b

Deprecated. This function is no longer necessary or useful.

O(\log n). seqSpine q r forces the spine of q and returns r.

Note: The spine of a MaxQueue is stored somewhat lazily. In earlier versions of this package, some operations could produce chains of thunks along the spine, occasionally necessitating manual forcing. Now, all operations are careful to force enough to avoid this problem.