Hi, I thought I may look at the :next command for GHCi debugger again. If I do, I will not make it before 6.12.1 is out. I have few questions about RTS in relation to :next implementation. If they is easy to answer I would appreciate it, if not, don't bother since I'm not sure I'll do it ... and If I decide to do it I may just figure it out myself or fail again :) Why is stg_nofoceIO_info added as last argument to IO actions in unregistered mode? Do I still need to pass it in even when (I think) my IO action does not need it? E.g. is it required for every IO action by some stack walking code or something? Are there any Cmm functions in RTS with signature (IO()) or signature (Int->IO()) which I could check out as examples to see how they are done? ... and ideally also how they are called from the stack. Are there any special things to do when adding a new field (e.g. simulated stack size) to StgTSO? Thanks, Peter.