T13233.hs:22:16: error:
    A levity-polymorphic type is not allowed here:
      Type: a
      Kind: TYPE rep1
    When trying to create a variable of type: a

T13233.hs:27:10: error:
    Cannot use function with levity-polymorphic arguments:
      mkWeak# :: a
                 -> b
                 -> (State# RealWorld -> (# State# RealWorld, c #))
                 -> State# RealWorld
                 -> (# State# RealWorld, Weak# b #)
    (Note that levity-polymorphic primops such as 'coerce' and unboxed tuples
    are eta-expanded internally because they must occur fully saturated.
    Use -fprint-typechecker-elaboration to display the full expression.)
    Levity-polymorphic arguments: a :: TYPE rep