| 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 htor
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 htFirstly, 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.
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.
Minimal complete definition
new, newSized, mutate, insert, delete, lookup, foldM, mapM_, lookupIndex, nextByIndex, computeOverhead
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).
mutate :: (Eq k, Hashable k) => h s k v -> k -> (Maybe v -> (Maybe v, a)) -> ST s a Source #
Generalized update. Given a key k, and a user function f, calls:
- `f Nothing` if the key did not exist in the hash table
- `f (Just v)` otherwise
If the user function returns (Nothing, _), then the value is deleted
from the hash table. Otherwise the mapping for k is inserted or
replaced with the provided value.
Returns the second part of the tuple returned by f.
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).
lookupIndex :: (Eq k, Hashable k) => h s k v -> k -> ST s (Maybe Word) Source #
Looks up the index of a key-value mapping in a hash table suitable
for passing to nextByIndex.
nextByIndex :: h s k v -> Word -> ST s (Maybe (Word, k, v)) Source #
Returns the next key-value mapping stored at the given index or at a greater index. The index, key, and value of the next record are returned.
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).
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).