T12709.hs:28:13: error: [GHC-55287]
    • The argument ‘1’ of ‘(+)’
      does not have a fixed runtime representation.
      Its type is:
        a0 :: TYPE rep0
      Cannot unify ‘rep’ with the type variable ‘rep0’
      because it is not a concrete ‘RuntimeRep’.
    • In the expression: 1 + 2 + 3 + 4
      In an equation for ‘u’: u = 1 + 2 + 3 + 4
      In the expression:
        let
          u :: Num (a :: TYPE rep) => a
          u = 1 + 2 + 3 + 4
        in BUB u u
    • Relevant bindings include u :: a (bound at T12709.hs:28:9)