tcfail179.hs:14:39:
    Couldn't match expected type ‛s’ with actual type ‛x’
      ‛x’ is a rigid type variable bound by
          a pattern with constructor
            T :: forall s x. (s -> (x -> s) -> (x, s, Int)) -> T s,
          in a case alternative
          at tcfail179.hs:14:14
      ‛s’ is a rigid type variable bound by
          the type signature for run :: T s -> Int at tcfail179.hs:12:8
    Relevant bindings include
      run :: T s -> Int (bound at tcfail179.hs:13:1)
      ts :: T s (bound at tcfail179.hs:13:5)
      g :: s -> (x -> s) -> (x, s, Int) (bound at tcfail179.hs:14:16)
      x :: x (bound at tcfail179.hs:14:26)
    In the first argument of ‛g’, namely ‛x’
    In the expression: g x id
    In a pattern binding: (x, _, b) = g x id