LRU-0.1.1: Implements an LRU data structure



This module implements a least-recently-used structure. Conceptually, it's a list of values where the head of the list is the most recently used value. When a value is used, it's moved from its place in the list to the head of the list. The last element in the list is thus the least-recently-used value.

This structure is often used in caches to decide which values to evict when the cache becomes full.

This module uses a Map to implement the LRU efficiently and thus there's the requirement that the elements of the LRU be instances of Ord, which a more general (but slower) LRU implementation could avoid.



data Ord a => LRU a Source

An LRU. Contains the head element, last element and the map from elements to their Items


(Ord a, Show a) => Show (LRU a) 

empty :: Ord a => LRU aSource

Returns an empty LRU. O(1)

null :: Ord a => LRU a -> BoolSource

Returns True iff the LRU is empty. O(1)

size :: Ord a => LRU a -> IntSource

Returns the number of elements in the LRU. O(1)

hit :: Ord a => a -> LRU a -> LRU aSource

Insert a value into an LRU. If the value is already in the LRU, it's moved to the head of the list. O(log n)

delete :: Ord a => a -> LRU a -> LRU aSource

Removes an element from the LRU, if it exists. O(log n)

toList :: Ord a => LRU a -> [a]Source

Returns a list of the members of the LRU in order, newest first. O(n(log n))

member :: Ord a => a -> LRU a -> BoolSource

Returns true iff the given element is in the LRU. O(log n)

pop :: Ord a => LRU a -> LRU aSource

Remove the last element of the LRU. Errors out if the LRU is empty. O(log n)

last :: (Ord a, Monad m) => LRU a -> m aSource

Return the last element of the LRU. O(1)