Hi Haskell Lovers, Im trying to compile Vertigo (http://conal.net/Vertigo), which seems to be a module from which I can really learn a lot of stuff. However, it seems to use a Memo module, which does not seem to be part of GHC (anymore?) As far as I understand, it uses a memo function to make sure that when performing symbolic differentiation, it does not get stuck in an endless loop. As I realize no generic memoization function can be made, I guess it got removed at some point? Can anyone give me a hint how to find a suitable Memo module for Vertigo? As a sidenote, I must say the memoization section on Haskell.org is not really helpful for a newbie like me... Thanks, Peter PS: I adapted the following code from SOE, but I'm not sure it does the job correctly (it will certainly be slow...) {-# OPTIONS_GHC -fglasgow-exts #-} module Memo(memo) where import Data.IORef import System.IO.Unsafe memo :: Eq a => (a->b) -> (a->b) memo f = unsafePerformIO $ do cache <- newIORef [] return $ \x -> unsafePerformIO $ do vals <- readIORef cache case x `inCache` vals of Nothing -> do let y = f x modifyIORef cache ((x,y):) return y Just y -> do return y inCache :: Eq a => a -> [(a,b)] -> Maybe b x `inCache` [] = Nothing x `inCache` ((x',y'):xys) = if x == x' then Just y' else x `inCache` xys