T13233_elab.hs:25:16: error:
    A levity-polymorphic type is not allowed here:
      Type: a
      Kind: TYPE rep1
    When trying to create a variable of type: a

T13233_elab.hs:33:10: error:
    Cannot use function with levity-polymorphic arguments:
      mkWeak# @rep @a @b @c :: a
                               -> b
                               -> (State# RealWorld -> (# State# RealWorld, c #))
                               -> State# RealWorld
                               -> (# State# RealWorld, Weak# b #)
    Levity-polymorphic arguments: a :: TYPE rep