I've been toying with a little thread manager library, and for sanity's sake I really need a way to install another top-level exception handler on an existing thread. I don't want to replace any other handlers, just put my own handler around the thread's continuation. Of course, it would be pretty easy to do if the IO monad had a nice efficient implementation of call/cc and call/cc1, although I don't need the full power of continuations. I really don't want to create my own "Thread" monad (which could use ContT), I want to be able to do it on plain old IO threads. Is there any way to do this in GHC? Best, Leon