What about something like:

import Data.IORef ( IORef, newIORef, readIORef, writeIORef )

newCounter :: IO (IO Int)

newCounter = do

counterRef <- newIORef 0 :: IO (IORef Int)

let getCount :: IO Int

getCount = do

count <- readIORef counterRef

writeIORef counterRef (count + 1)

return count

return getCount

The user calls this function which creates the cache and returns the stateful function. You can use MVars instead of IORefs if you want it to work concurrently.

On Sun, Jul 8, 2018 at 2:29 AM Dennis Raddle <dennis.raddle@gmail.com> wrote:

In this one use case, there might be a simpler solution, but I have encountered lots of situations in which a particular algorithm could benefit from an associated stored cache of information. The most natural way to write an algorithm, sometimes, is in terms of its past decisions or past state of the program, interacting with current state.

D

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