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

[John Smith]

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