Safe Haskell	None
Language	Haskell98

Data.HashTable.Class

Description

This module contains a HashTable typeclass for the hash table implementations in this package. This allows you to provide functions which will work for any hash table implementation in this collection.

It is recommended to create a concrete type alias in your code when using this package, i.e.:

import qualified Data.HashTable.IO as H

type HashTable k v = H.BasicHashTable k v

foo :: IO (HashTable Int Int)
foo = do
    ht <- H.new
    H.insert ht 1 1
    return ht

or

import qualified Data.HashTable.ST.Cuckoo as C
import qualified Data.HashTable.Class as H

type HashTable s k v = C.HashTable s k v

foo :: ST s (HashTable s k v)
foo = do
    ht <- H.new
    H.insert ht 1 1
    return ht

Firstly, this makes it easy to switch to a different hash table implementation, and secondly, using a concrete type rather than leaving your functions abstract in the HashTable class should allow GHC to optimize away the typeclass dictionaries.

Note that the functions in this typeclass are in the ST monad; if you want hash tables in IO, use the convenience wrappers in Data.HashTable.IO.

Synopsis

Documentation

class HashTable h where Source

A typeclass for hash tables in the ST monad. The operations on these hash tables are typically both key- and value-strict.

Methods

new :: ST s (h s k v) Source

Creates a new, default-sized hash table. O(1).

newSized :: Int -> ST s (h s k v) Source

Creates a new hash table sized to hold n elements. O(n).

insert :: (Eq k, Hashable k) => h s k v -> k -> v -> ST s () Source

Inserts a key/value mapping into a hash table, replacing any existing mapping for that key.

O(n) worst case, O(1) amortized.

delete :: (Eq k, Hashable k) => h s k v -> k -> ST s () Source

Deletes a key-value mapping from a hash table. O(n) worst case, O(1) amortized.

lookup :: (Eq k, Hashable k) => h s k v -> k -> ST s (Maybe v) Source

Looks up a key-value mapping in a hash table. O(n) worst case, (O(1) for cuckoo hash), O(1) amortized.

foldM :: (a -> (k, v) -> ST s a) -> a -> h s k v -> ST s a Source

A strict fold over the key-value records of a hash table in the ST monad. O(n).

mapM_ :: ((k, v) -> ST s b) -> h s k v -> ST s () Source

A side-effecting map over the key-value records of a hash table. O(n).

computeOverhead :: h s k v -> ST s Double Source

Computes the overhead (in words) per key-value mapping. Used for debugging, etc; time complexity depends on the underlying hash table implementation. O(n).

Instances

HashTable HashTable
HashTable HashTable
HashTable HashTable

fromList :: (HashTable h, Eq k, Hashable k) => [(k, v)] -> ST s (h s k v) Source

Create a hash table from a list of key-value pairs. O(n).

fromListWithSizeHint :: (HashTable h, Eq k, Hashable k) => Int -> [(k, v)] -> ST s (h s k v) Source

Create a hash table from a list of key-value pairs, with a size hint. O(n).

toList :: HashTable h => h s k v -> ST s [(k, v)] Source

Given a hash table, produce a list of key-value pairs. O(n).