tcfail065.hs:29:20: error: [GHC-25897]
    • Couldn't match expected type ‘x’ with actual type ‘x1’
      ‘x1’ is a rigid type variable bound by
        the type signature for:
          setX :: forall x1. x1 -> X x -> X x
        at tcfail065.hs:29:3-6
      ‘x’ is a rigid type variable bound by
        the instance declaration
        at tcfail065.hs:28:10-19
    • In the first argument of ‘X’, namely ‘x’
      In the expression: X x
      In an equation for ‘setX’: setX x (X _) = X x
    • Relevant bindings include
        x :: x1 (bound at tcfail065.hs:29:8)
        setX :: x1 -> X x -> X x (bound at tcfail065.hs:29:3)