Hashcode for reference

Hi all, I'm wondering if there is a way to get an hashcode from references (IORef or STRef)? I have looked in the library and a little in the sources of GHC but haven't found anything allowing to do this. I'm generating Haskell code from the Isabelle/HOL proof assistant, which generate "generic" code for other langages too which all have this notion, and I would so need an equivalent in Haskell. Have you any hint on how to achieve this, or even if it is possible? Mathieu