Typechecked:
AbsBinds [] [] [(fubar.t439, Main.fubar{-r79-})]
    {- nonrec -}
    fubar.t439 :: IoWorld -> (Int, IoWorld)
    fubar.t439
	= (thenIO_{-r99-} [bpv83, Int]) (ccall  f [bpv83] ) (ccall  b [Int] )
{- nonrec -}
{- nonrec -}
Desugared:

Fail: panic! (the `impossible' happened):
	getBoxedPrimTypeInfo: bpv83

Please report it as a compiler bug to glasgow-haskell-bugs@dcs.glasgow.ac.uk.