[Haskell] Data.Hashtable operations in IO?

[ROBERT DOUGLAS HOELZ]

I was reading the docs for Data.Hashtable, and quickly noticed that operations on a hashtable are of the IO monad.  Why is this?  I should think that the operations would look like this:

insert :: Hashtable -> key -> val -> Hashtable
lookup :: Hashtable -> key -> a

etc.

Thanks,
Rob Hoelz