request for a cachedIOWithSTM'

[Vlix]

It's somewhat unfortunate you can't create the cached value inside the STM monad.

I have a situation where I need to inspect some TVars first before deciding whether to create a new Cached value, and the golden path is that it doesn't have to be created, so in general I will be creating unnecessary Cached values to then ignore them.

With the following tweak, it would be an easy addition, I feel.

-- >> New base for all other functions instead of 'cachedIOWith''
cachedIOWithSTM'
    :: (MonadIO t, MonadCatch t)
    => (UTCTime -> UTCTime -> Bool)
    -> (Maybe (UTCTime, a) -> t a)
    -> STM (Cached t a)
cachedIOWithSTM' isCacheStillFresh io = do
  cachedT <- newTVar Uninitialized
  pure . Cached $ do
    ...

-- >> Defined in terms of 'cachedIOWithSTM''
cachedIOWith' isCacheStillFresh io =
  liftIO . atomically $ cachedIOWithSTM' isCachedStillFresh io