gistfile1.hs

data Param m k v = Param {
    cacheSize :: Int
  , table     :: H.HashTableSTM k (Ref v)
  , toIO      :: forall a. m a -> IO a
  , lock      :: TVar Int
  }

newtype CacheSTM m k v a = CacheSTM { runCacheSTM :: ReaderT (Param m k v) STM a }
                         deriving (Monad, MonadReader (Param m k v), Functor)

evalCacheSTM :: Param m k v -> CacheSTM m k v a -> IO a
evalCacheSTM p m =
  atomically $ runReaderT (runCacheSTM m) p

sizedParam :: Int -> (forall a. m a -> IO a) -> IO (Param m k v)
sizedParam s f = do
  ht <- H.newSized s
  mv <- atomically $ newTVar 0
  return $ Param s ht f mv