Hi all, I'm working on pulling the core parts of Joachim Breitner's ghc-heap-view library into GHC. The WIP Phab review is here: https://phabricator.haskell.org/D3055 Currently that library has a function: getClosureData :: a -> IO Closure which works fine for lifted types. However, some of the supported closure types in http://hackage.haskell.org/trac/ghc/browser/includes/rts/storage/InfoTables.... actually refer to unlifted types, like the `MUT_ARR_PTRS_*` and `SMALL_MUT_ARR_PTRS_*`. I've had a look at the levity polymorphism stuff implemented in ghc 8.0 and came up with a new type for `getClosureData`: getClosureData :: forall (r :: RuntimeRep) (a :: TYPE r). a -> IO Closure but that results in: A representation-polymorphic type is not allowed here: Type: a Kind: TYPE r In the type of binder ‘x’ Am I barking up the wrong tree here? Any one have a clue on how I might make progress on this? Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/