RepPolyTuple2.hs:21:9: error: [GHC-55287]
    • Unsaturated use of a representation-polymorphic data constructor.
      The second argument of ‘(#,#)’
      does not have a fixed runtime representation.
      Its type is:
        b :: TYPE RR
    • In the expression: (#,#) @LiftedRep @RR (expensive x)
      In an equation for ‘tup’:
          tup x = (#,#) @LiftedRep @RR (expensive x)