Control.Concurrent.CachedIO

Example usage:

-- Downloads a large payload from an external data store.
downloadData :: IO ByteString

cachedDownloadData :: IO (Cached IO ByteString)
cachedDownloadData = cachedIO (secondsToNominalDiffTime 600) downloadData

The first time cachedDownloadData is called, it calls downloadData, stores the result, and returns it. If it is called again:

• before 10 minutes have passed, it returns the stored value.
• after 10 minutes have passed, it calls downloadData and stores the result again.

Documentation

newtype Cached m a

A cached IO action in some monad m. Use runCached to extract the action when you want to query it.

Note that using join when the cached action and the outer monad are the same will ignore caching.

Constructors

Cached

Fields

• runCached :: m a

cachedIO

Arguments

:: (MonadIO m, MonadIO t, MonadCatch t)

=> NominalDiffTime

Number of seconds before refreshing cache

-> t a

IO action to cache

-> m (Cached t a)

Cache an IO action, producing a version of this IO action that is cached for interval seconds. The cache begins uninitialized.

The outer IO is responsible for setting up the cache. Use the inner one to either get the cached value or refresh, if the cache is older than interval seconds.

cachedIOWith

Arguments

:: (MonadIO m, MonadIO t, MonadCatch t)

=> (UTCTime -> UTCTime -> Bool)

Test function: If isCacheStillFresh lastUpdated now returns True the cache is considered still fresh and returns the cached IO action

-> t a

action to cache.

-> m (Cached t a)

Cache an IO action, The cache begins uninitialized.

The outer IO is responsible for setting up the cache. Use the inner one to either get the cached value or refresh

cachedIO'

Arguments

:: (MonadIO m, MonadIO t, MonadCatch t)

=> NominalDiffTime

Number of seconds before refreshing cache

-> (Maybe (UTCTime, a) -> t a)

action to cache. The stale value and its refresh date are passed so that the action can perform external staleness checks

-> m (Cached t a)

Cache an IO action, producing a version of this IO action that is cached for interval seconds. The cache begins uninitialized.

The outer IO is responsible for setting up the cache. Use the inner one to either get the cached value or refresh, if the cache is older than interval seconds.

cachedIOWith'

Arguments

:: (MonadIO m, MonadIO t, MonadCatch t)

=> (UTCTime -> UTCTime -> Bool)

Test function: If isCacheStillFresh lastUpdated now returns True the cache is considered still fresh and returns the cached IO action

-> (Maybe (UTCTime, a) -> t a)

action to cache. The stale value and its refresh date are passed so that the action can perform external staleness checks

-> m (Cached t a)

Cache an IO action, The cache begins uninitialized.

The outer IO is responsible for setting up the cache. Use the inner one to either get the cached value or refresh