[boost] [Fusion] Tentative of trasnform_if failed :(

The following code http://ideone.com/xYk4X doesn't compile and i cant get the why of it. The goal is to have a fusion transform_if that takes a compile-time predicates For each element int he sequence, if the predicates its true, we apply some transform on it, if not we return the element unchanged. What am I missing ?