Hi. I want to use GHCi as the interface to my Application. The simple solution is to have the Application store its state in global IORefs. A user can then start up ghci with -package Application and use the provided functions to communicate with the Application. This works nicely. Now the tricky part. I want the user to be able to implement her own layers on top of the Application API. A typical user interaction could look something like this: $ ghci -package Application *Application:API> startApplication *Application:API> :load UserLayer *main:UserLayer> myCleverFunction 42 The problem, of course, is that as soon as the user says ':load' ghci forgets all about the state of the Application. My solution to the problem is to compile my own version of ghci (copy InteractiveUI.hs and use -package ghc) and remove the call to rts_revertCAFs when loading new modules. This seems to work, but since I don't really have a clue what I'm doing I wanted to ask a few questions: 1) What is a CAF? 2) What breaks down if you don't revert them? 3) Does not reverting the CAFs really solve my problem? / Ulf