Data.HashTable.Class

hashtables-1.2.0.1: Mutable hash tables in the ST monad

Safe Haskell | Safe
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

- class HashTable h where
  - new :: ST s (h s k v)
  - newSized :: Int -> ST s (h s k v)
  - insert :: (Eq k, Hashable k) => h s k v -> k -> v -> ST s ()
  - delete :: (Eq k, Hashable k) => h s k v -> k -> ST s ()
  - lookup :: (Eq k, Hashable k) => h s k v -> k -> ST s (Maybe v)
  - foldM :: (a -> (k, v) -> ST s a) -> a -> h s k v -> ST s a
  - mapM_ :: ((k, v) -> ST s b) -> h s k v -> ST s ()
  - computeOverhead :: h s k v -> ST s Double
- fromList :: (HashTable h, Eq k, Hashable k) => [(k, v)] -> ST s (h s k v)
- fromListWithSizeHint :: (HashTable h, Eq k, Hashable k) => Int -> [(k, v)] -> ST s (h s k v)
- toList :: HashTable h => h s k v -> ST s [(k, v)]

# Documentation

class HashTable h where

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)

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

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

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 ()

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 ()

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)

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

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 ()

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

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

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)

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)

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)]

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