Simon Peyton-Jones wrote: > (Unsatisfactory but would work) You could compile with -ddump-ds and > look at the output. Yes, I did work (for VariableList.hs) attachListOp :: forall pos . ParallelExec -> ListDrawer a pos -> IO (IO ()) Thanks, Christian (I need to get a new ghc-6.5 without the overlapping-instances bug for further tests)