Hello, I noticed the stm types TMVar and TChan don't have Typeable and Eq instances while their MVar counterparts do have them. I propose to add them: http://hackage.haskell.org/trac/ghc/ticket/3973 The patch bundle included in the ticket also contains patches that add these instances to TArray. However I'm not sure if it makes sense to have an Eq instance for TArray so it's probably wise to have some discussion on this. regards, Bas