T13610.hs:11:15: error:
    • Couldn't match a lifted type with an unlifted type
      When matching types
        a :: *
        Weak# () :: TYPE 'UnliftedRep
      Expected: (# State# RealWorld, a #)
        Actual: (# State# RealWorld, Weak# () #)
    • In the expression: mkWeakNoFinalizer# double () s
      In the first argument of ‘IO’, namely
        ‘(\ s -> mkWeakNoFinalizer# double () s)’
      In a stmt of a 'do' block:
        IO (\ s -> mkWeakNoFinalizer# double () s)
    • Relevant bindings include main :: IO a (bound at T13610.hs:8:1)