Hi, I'm trying to attach (f Void#) as a compulsory unfolding to an Id. Here's what I tried originally: let unfolding = mkCoreApp (Var worker_id) (Var voidPrimId) wrapper_id' = setIdUnfolding wrapper_id $ mkCompulsoryUnfolding unfolding However, when I try to use wrapper_id' in the desugarer, the Core linter looks at me strange. This is the original Core: f :: Int [LclIdX, Str=DmdType] f = break<1>() GHC.Types.I# Main.$WPAT and this is the error message ($WPAT is the wrapper_id', PAT is the worker_id in this example) <no location info>: Warning: In the expression: I# (PAT void#) This argument does not satisfy the let/app invariant: PAT void# Now, I thought I'd make sure mkCoreApp generated correct Core by writing it out by hand: let unfolding = Case (Var voidPrimId) voidArgId pat_ty [(DEFAULT,[],App (Var worker_id) (Var voidArgId))] however, bizarrely, this *still* results in *the same* error message, as if something was transforming it back to a straight App. Anyone have any hints what I'm doing wrong here? Bye, Gergo -- .--= ULLA! =-----------------. \ http://gergo.erdi.hu \ `---= gergo@erdi.hu =-------' You are in a twisty maze of little install diskettes.