[Haskell-cafe] Question about HList possibilities

Hello all, Given an HList (http://homepages.cwi.nl/~ralf/HList/) would it be possible to do the following: Create a class/function/magicks that would essentially do what hOccursMany does, except it would not return a list of elements, but a new HList. For example, would this allow us to be able to write more lax typing constraints and say extract only things that are in lists. ie) HCons "hi" (HCons [2.2,3.3] (HCons 'a' hNil)) -> HCons "hi" (HCons [2.2,3.3] hNil) (removing the Char element). I tried to write something like this but I did not get very far, is it even possible? I'm new to this type-level programming :) Scott