T3330a.hs:19:34: error:
    • Couldn't match type ‘ix’
                     with ‘r ix1 -> Writer [AnyF s] (r'0 ix1)’
      ‘ix’ is a rigid type variable bound by
        the type signature for:
          children :: forall (s :: * -> *) ix (r :: * -> *).
                      s ix -> PF s r ix -> [AnyF s]
        at T3330a.hs:18:1-43
      Expected type: (s0 ix0 -> ix1)
                     -> r ix1 -> Writer [AnyF s] (r'0 ix1)
        Actual type: s ix
    • In the first argument of ‘hmapM’, namely ‘p’
      In the first argument of ‘execWriter’, namely ‘(hmapM p collect x)’
      In the expression: execWriter (hmapM p collect x)
    • Relevant bindings include
        x :: PF s r ix (bound at T3330a.hs:19:12)
        p :: s ix (bound at T3330a.hs:19:10)
        children :: s ix -> PF s r ix -> [AnyF s] (bound at T3330a.hs:19:1)

T3330a.hs:19:44: error:
    • Couldn't match type ‘ix’
                     with ‘r0 ix0 -> Writer [AnyF s0] (r0 ix0)’
      ‘ix’ is a rigid type variable bound by
        the type signature for:
          children :: forall (s :: * -> *) ix (r :: * -> *).
                      s ix -> PF s r ix -> [AnyF s]
        at T3330a.hs:18:1-43
      Expected type: PF s r (r0 ix0 -> Writer [AnyF s0] (r0 ix0))
        Actual type: PF s r ix
    • In the third argument of ‘hmapM’, namely ‘x’
      In the first argument of ‘execWriter’, namely ‘(hmapM p collect x)’
      In the expression: execWriter (hmapM p collect x)
    • Relevant bindings include
        x :: PF s r ix (bound at T3330a.hs:19:12)
        p :: s ix (bound at T3330a.hs:19:10)
        children :: s ix -> PF s r ix -> [AnyF s] (bound at T3330a.hs:19:1)