RepPolyArgument.hs:10:18: error: [GHC-55287]
    • The argument ‘(undefined @(R @RuntimeRep))’ of ‘undefined’
      does not have a fixed runtime representation.
      Its type is:
        t0 :: TYPE c0
      Cannot unify ‘R’ with the type variable ‘c0’
      because it is not a concrete ‘RuntimeRep’.
    • In the first argument of ‘undefined’, namely
        ‘(undefined @(R @RuntimeRep))’
      In the expression: undefined (undefined @(R @RuntimeRep))
      In an equation for ‘foo’:
          foo = undefined (undefined @(R @RuntimeRep))