res' :: [MediaType] -> Maybe ResolutionDer
res' (x:xs) = case x of
    (Resolution a) -> Just a
    _ -> res' xs
res' :: [MediaType] -> Maybe ResolutionDer
res' (x:xs) = case x of
    (Resolution a) -> Just a
    _ -> res' xs
res' (x:xs) = case x of
    (Resolution a) -> Just a
    _ -> res' xs