Re: [Haskell-cafe] Troubles understanding memoization in SOE

24 Sep 2007


      On Sat, 22 Sep 2007, Peter Verswyvelen wrote:
...
Hi,
in SOE, the following memoization function is implemented:
memo1 :: (a->b) -> (a->b)
memo1 f = unsafePerformIO $ do
cache <- newIORef []
return $ \x -> unsafePerformIO $ do
            vals <- readIORef cache
            case x `inCache` vals of
              Nothing -> do let y = f x
                            writeIORef cache [(x,y)] -- ((x,y) : -- 
if null vals then [] else [head vals])
                            return y
              Just y  -> do return y
Hm, why the unsafePerformIO hacks? It should be possible without:
   http://www.haskell.org/haskellwiki/Memoization

Re: [Haskell-cafe] Troubles understanding memoization in SOE

Henning Thielemann