clos <- trIO $ getClosureData a
case tipe clos of
-- Thunks we may want to force
--- NB. this won't attempt to force a BLACKHOLE. Even with :force, we never
--- force blackholes, because it would almost certainly result in deadlock,
--- and showing the '_' is more useful.
t | isThunk t && force -> traceTR (text "Forcing a " <> text (show t)) >>
seq a (go (pred max_depth) my_ty old_ty a)
+-- Blackholes are indirections iff the payload is not TSO or BLOCKING_QUEUE. So we
+-- treat them like indirections; if the payload is TSO or BLOCKING_QUEUE, we'll end up
+-- showing '_' which is what we want.
+ Blackhole -> do traceTR (text "Following a BLACKHOLE")
+ appArr (go max_depth my_ty old_ty) (ptrs clos) 0
-- We always follow indirections
Indirection i -> do traceTR (text "Following an indirection" <> parens (int i) )
go max_depth my_ty old_ty $! (ptrs clos ! 0)
go my_ty a = do
clos <- trIO $ getClosureData a
case tipe clos of
+ Blackhole -> appArr (go my_ty) (ptrs clos) 0 -- carefully, don't eval the TSO
Indirection _ -> go my_ty $! (ptrs clos ! 0)
MutVar _ -> do
contents <- trIO$ IO$ \w -> readMutVar# (unsafeCoerce# a) w