tcfail065.hs:29:18: error:
    • Couldn't match type ‘x1’ with ‘x’
      ‘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
      Expected type: X x
        Actual type: X x1
    • In the expression: X x
      In an equation for ‘setX’: setX x (X _) = X x
      In the instance declaration for ‘HasX (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)