gistfile1.txt

task1.hs:43:22:
    Could not deduce (a ~ Query)
    from the context (Data a)
      bound by a type expected by the context: Data a => a -> a
      at task1.hs:(42,14)-(44,22)
      `a' is a rigid type variable bound by
          a type expected by the context: Data a => a -> a at task1.hs:42:14
    In the expression: a
    In a case alternative: (SNot (SNot a)) -> a
    In the expression:
      case node of {
        (SNot (SNot a)) -> a
        otherwise -> node }
Failed, modules loaded: none.