Thanks to reactions! What do you think about such a function? This function is still a bit dangerous (I think). I don't know how to make sure the compiler does not lift cache to something global. But on the other hand this use of unsafePerformIO is legit because it doesn't alter the referential transparency of the function. The same as in DiffArray. Greetings Gerben memo f = let cache = unsafePerformIO $ newIORef M.empty cachedFunc x = unsafePerformIO (do m <- readIORef cache case M.lookup x m of Just y -> return y Nothing -> do let res = f x writeIORef cache $ M.insert x res m return res) in cachedFunc memo2 f = curry $ memo $ uncurry f -- View this message in context: http://www.nabble.com/memoization-tp25306687p25381881.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.