Safe Haskell	Safe-Inferred
Language	Haskell98

Data.Cache.LRU.Internal

Description

This module provides access to all the internals use by the LRU type. This can be used to create data structures that violate the invariants the public interface maintains. Be careful when using this module. The valid function can be used to check if an LRU structure satisfies the invariants the public interface maintains.

If this degree of control isn't needed, consider using Data.Cache.LRU instead.

Synopsis

Documentation

data LRU key val Source

Stores the information that makes up an LRU cache

Constructors

LRU
Fields first :: !(Maybe key) the key of the most recently accessed entry last :: !(Maybe key) the key of the least recently accessed entry maxSize :: !(Maybe Integer) the maximum size of the LRU cache content :: !(Map key (LinkedVal key val)) the backing `Map`

Instances

Functor (LRU key)
Ord key => Foldable (LRU key)
Ord key => Traversable (LRU key)
(Eq key, Eq val) => Eq (LRU key val)
(Data key, Data val, Ord key) => Data (LRU key val)
(Ord key, Show key, Show val) => Show (LRU key val)
Typeable (* -> * -> *) LRU

data LinkedVal key val Source

The values stored in the Map of the LRU cache. They embed a doubly-linked list through the values of the Map.

Constructors

Link
Fields value :: val The actual value prev :: !(Maybe key) the key of the value before this one next :: !(Maybe key) the key of the value after this one

Instances

Functor (LinkedVal key)
Foldable (LinkedVal key)
Traversable (LinkedVal key)
(Eq key, Eq val) => Eq (LinkedVal key val)
(Data key, Data val) => Data (LinkedVal key val)
Typeable (* -> * -> *) LinkedVal

newLRU Source

Arguments

:: Ord key
=> Maybe Integer	the optional maximum size of the LRU
-> LRU key val

Make an LRU. If a size limit is specified, the LRU is guaranteed to not grow above the specified number of entries.

fromList Source

Arguments

:: Ord key
=> Maybe Integer	the optional maximum size of the LRU
-> [(key, val)]
-> LRU key val

Build a new LRU from the given maximum size and list of contents, in order from most recently accessed to least recently accessed.

toList :: Ord key => LRU key val -> [(key, val)] Source

Retrieve a list view of an LRU. The items are returned in order from most recently accessed to least recently accessed.

pairs :: (Ord key, Applicative f, Contravariant f) => ((key, val) -> f (key, val)) -> LRU key val -> f (LRU key val) Source

Traverse the (key, value) pairs of the LRU, in a read-only way. This is a Fold in the sense used by the lens package. It must be read-only because alterations could break the underlying Map structure.

keys :: (Ord key, Applicative f, Contravariant f) => (key -> f key) -> LRU key val -> f (LRU key val) Source

Traverse the keys of the LRU, in a read-only way. This is a Fold in the sense used by the lens package. It must be read-only because alterations could break the underlying Map structure.

insert :: Ord key => key -> val -> LRU key val -> LRU key val Source

Add an item to an LRU. If the key was already present in the LRU, the value is changed to the new value passed in. The item added is marked as the most recently accessed item in the LRU returned.

If this would cause the LRU to exceed its maximum size, the least recently used item is dropped from the cache.

insertInforming :: Ord key => key -> val -> LRU key val -> (LRU key val, Maybe (key, val)) Source

Same as insert, but also returns element which was dropped from cache, if any.

lookup :: Ord key => key -> LRU key val -> (LRU key val, Maybe val) Source

Look up an item in an LRU. If it was present, it is marked as the most recently accesed in the returned LRU.

delete :: Ord key => key -> LRU key val -> (LRU key val, Maybe val) Source

Remove an item from an LRU. Returns the new LRU, and the value removed if the key was present.

pop :: Ord key => LRU key val -> (LRU key val, Maybe (key, val)) Source

Removes the least-recently accessed element from the LRU. Returns the new LRU, and the key and value from the least-recently used element, if there was one.

size :: LRU key val -> Int Source

Returns the number of elements the LRU currently contains.

hit' :: Ord key => key -> LRU key val -> LRU key val Source

Internal function. The key passed in must be present in the LRU. Moves the item associated with that key to the most recently accessed position.

delete' Source

Arguments

:: Ord key
=> key	The key must be present in the provided `LRU`
-> LRU key val	This is the `LRU` to modify
-> Map key (LinkedVal key val)	this is the `Map` from the previous argument, but with the key already removed from it. This isn't consistent yet, as it still might contain LinkedVals with pointers to the removed key.
-> LinkedVal key val	This is the `LinkedVal` that corresponds to the key in the passed in LRU. It is absent from the passed in map.
-> LRU key val

An internal function used by insert (when the cache is full) and delete. This function has strict requirements on its arguments in order to work properly.

As this is intended to be an internal function, the arguments were chosen to avoid repeated computation, rather than for simplicity of calling this function.

adjust' :: Ord k => (a -> a) -> k -> Map k a -> Map k a Source

Internal function. This is very similar to adjust, with two major differences. First, it's strict in the application of the function, which is a huge win when working with this structure.

Second, it requires that the key be present in order to work. If the key isn't present, undefined will be inserted into the Map, which will cause problems later.

valid :: Ord key => LRU key val -> Bool Source

Internal function. This checks the four structural invariants of the LRU cache structure:

The cache's size does not exceed the specified max size.
The linked list through the nodes is consistent in both directions.
The linked list contains the same number of nodes as the cache.
Every key in the linked list is in the Map.