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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Moduleghc-9.10.3GHC2021

GHC.Data.Word64Set.Internal

WARNING

This module is considered internal.

The Package Versioning Policy does not apply.

The contents of this module may change in any way whatsoever and without any warning between minor versions of this package.

Authors importing this module are expected to track development closely.

Description

An efficient implementation of integer sets.

These modules are intended to be imported qualified, to avoid name clashes with Prelude functions, e.g.

 import Data.Word64Set (Word64Set)
 import qualified Data.Word64Set as Word64Set

The implementation is based on big-endian patricia trees. This data structure performs especially well on binary operations like union and intersection. However, my benchmarks show that it is also (much) faster on insertions and deletions when compared to a generic size-balanced set implementation (see Data.Set).

  • Chris Okasaki and Andy Gill, "Fast Mergeable Integer Maps", Workshop on ML, September 1998, pages 77-86, http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.37.5452

  • D.R. Morrison, "PATRICIA -- Practical Algorithm To Retrieve Information Coded In Alphanumeric", Journal of the ACM, 15(4), October 1968, pages 514-534.

Additionally, this implementation places bitmaps in the leaves of the tree. Their size is the natural size of a machine word (32 or 64 bits) and greatly reduce memory footprint and execution times for dense sets, e.g. sets where it is likely that many values lie close to each other. The asymptotics are not affected by this optimization.

Many operations have a worst-case complexity of O(\min(n,W)). This means that the operation can become linear in the number of elements with a maximum of W -- the number of bits in an Int (32 or 64).

  • 5 types
  • 58 values
  • Packageghc-9.10.3
  • Exports63
  • LanguageGHC2021
  • LicenceBSD-3-Clause
  • SourceInternal.hs

Set type

5 declarations
datadata Word64Set
#

A set of integers.

Instances11IsList, Eq, Data, Ord, Read, Show, …

Operators

1 declaration

Query

11 declarations
valuelookupLT :: Key -> Word64Set -> Maybe Key
#

O(\min(n,W)). Find largest element smaller than the given one.

lookupLT 3 (fromList [3, 5]) == Nothing
lookupLT 5 (fromList [3, 5]) == Just 3
valuelookupGT :: Key -> Word64Set -> Maybe Key
#

O(\min(n,W)). Find smallest element greater than the given one.

lookupGT 4 (fromList [3, 5]) == Just 5
lookupGT 5 (fromList [3, 5]) == Nothing
valuelookupLE :: Key -> Word64Set -> Maybe Key
#

O(\min(n,W)). Find largest element smaller or equal to the given one.

lookupLE 2 (fromList [3, 5]) == Nothing
lookupLE 4 (fromList [3, 5]) == Just 3
lookupLE 5 (fromList [3, 5]) == Just 5
valuelookupGE :: Key -> Word64Set -> Maybe Key
#

O(\min(n,W)). Find smallest element greater or equal to the given one.

lookupGE 3 (fromList [3, 5]) == Just 3
lookupGE 4 (fromList [3, 5]) == Just 5
lookupGE 6 (fromList [3, 5]) == Nothing
valuedisjoint :: Word64Set -> Word64Set -> Bool
#

O(n+m). Check whether two sets are disjoint (i.e. their intersection is empty).

disjoint (fromList [2,4,6])   (fromList [1,3])     == True
disjoint (fromList [2,4,6,8]) (fromList [2,3,5,7]) == False
disjoint (fromList [1,2])     (fromList [1,2,3,4]) == False
disjoint (fromList [])        (fromList [])        == True

Construction

5 declarations
valuedelete :: Key -> Word64Set -> Word64Set
#

O(\min(n,W)). Delete a value in the set. Returns the original set when the value was not present.

Combine

4 declarations

Filter

8 declarations
valuesplit :: Key -> Word64Set -> (Word64Set, Word64Set)
#

O(\min(n,W)). The expression (split x set) is a pair (set1,set2) where set1 comprises the elements of set less than x and set2 comprises the elements of set greater than x.

split 3 (fromList [1..5]) == (fromList [1,2], fromList [4,5])
valuesplitRoot :: Word64Set -> [Word64Set]
#

O(1). Decompose a set into pieces based on the structure of the underlying tree. This function is useful for consuming a set in parallel.

No guarantee is made as to the sizes of the pieces; an internal, but deterministic process determines this. However, it is guaranteed that the pieces returned will be in ascending order (all elements in the first submap less than all elements in the second, and so on).

Examples:

splitRoot (fromList [1..120]) == [fromList [1..63],fromList [64..120]]
splitRoot empty == []

Note that the current implementation does not return more than two subsets, but you should not depend on this behaviour because it can change in the future without notice. Also, the current version does not continue splitting all the way to individual singleton sets -- it stops at some point.

Map

2 declarations
valuemap :: (Key -> Key) -> Word64Set -> Word64Set
#

O(n \min(n,W)). map f s is the set obtained by applying f to each element of s.

It's worth noting that the size of the result may be smaller if, for some (x,y), x /= y && f x == f y

valuemapMonotonic :: (Key -> Key) -> Word64Set -> Word64Set
#

O(n). The

mapMonotonic f s == map f s, but works only when f is strictly increasing. The precondition is not checked. Semi-formally, we have:

and [x < y ==> f x < f y | x <- ls, y <- ls]
                    ==> mapMonotonic f s == map f s
    where ls = toList s

Folds

2 declarations
valuefoldr :: (Key -> b -> b) -> b -> Word64Set -> b
#

O(n). Fold the elements in the set using the given right-associative binary operator, such that foldr f z == foldr f z . toAscList.

For example,

toAscList set = foldr (:) [] set
valuefoldl :: (a -> Key -> a) -> a -> Word64Set -> a
#

O(n). Fold the elements in the set using the given left-associative binary operator, such that foldl f z == foldl f z . toAscList.

For example,

toDescList set = foldl (flip (:)) [] set

Strict folds

valuefoldr' :: (Key -> b -> b) -> b -> Word64Set -> b
#

O(n). A strict version of foldr. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.

valuefoldl' :: (a -> Key -> a) -> a -> Word64Set -> a
#

O(n). A strict version of foldl. Each application of the operator is evaluated before using the result in the next application. This function is strict in the starting value.

Legacy folds

valuefold :: (Key -> b -> b) -> b -> Word64Set -> b
#

O(n). Fold the elements in the set using the given right-associative binary operator. This function is an equivalent of foldr and is present for compatibility only.

Please note that fold will be deprecated in the future and removed.

Min/Max

8 declarations

O(\min(n,W)). Delete the minimal element. Returns an empty set if the set is empty.

Note that this is a change of behaviour for consistency with Set – versions prior to 0.5 threw an error if the Word64Set was already empty.

O(\min(n,W)). Delete the maximal element. Returns an empty set if the set is empty.

Note that this is a change of behaviour for consistency with Set – versions prior to 0.5 threw an error if the Word64Set was already empty.

Conversion

0 declarations

List

valuetoList :: Word64Set -> [Key]
#

O(n). Convert the set to a list of elements. Subject to list fusion.

Ordered list

valuetoAscList :: Word64Set -> [Key]
#

O(n). Convert the set to an ascending list of elements. Subject to list fusion.

valuetoDescList :: Word64Set -> [Key]
#

O(n). Convert the set to a descending list of elements. Subject to list fusion.

valuefromAscList :: [Key] -> Word64Set
#

O(n). Build a set from an ascending list of elements. The precondition (input list is ascending) is not checked.

O(n). Build a set from an ascending list of distinct elements. The precondition (input list is strictly ascending) is not checked.

Debugging

2 declarations
valueshowTree :: Word64Set -> String
#

O(n \min(n,W)). Show the tree that implements the set. The tree is shown in a compressed, hanging format.

valueshowTreeWith :: Bool -> Bool -> Word64Set -> String
#

O(n \min(n,W)). The expression (showTreeWith hang wide map) shows the tree that implements the set. If hang is True, a hanging tree is shown otherwise a rotated tree is shown. If wide is True, an extra wide version is shown.

Internals

5 declarations