Re: [Haskell-cafe] Types and hashes of hashes, trouble for a Java-programmer...

If you mean using a non-destructive map where the IO-problem is absent, that is a doable thing. But it would be like cheating :-) What I try do do is something like: test = do   h <- HashTable.new (==) (\key -> key)   h1 <- HashTable.new (==) (\key -> key)   HashTable.insert h 3 h1   HashTable.insert h1 1 1000   res <- case HashTable.lookup h 3 of       Nothing -> Nothing       Just outer -> HashTable.lookup outer 1000   return res