[Haskell-cafe] Value-weak hash tables for GHC?

Hi, Does anyone have an implementation of value-weak hash tables for GHC he'd be willing to share? (Hash tables where an entry is removed when the value, not the key, is collected.) Since GHC has (usable) weak pointers, finalisers and hash tables, I could in principle roll my own, but I'd rather get an efficient implementation off someone competent. Oh, and it needs to be under a license that makes it suitable for inclusion in Darcs. Thanks a lot, Juliusz P.S. I am not subscribed to the list -- I'd be grateful if you could CC me with any replies.