-- | Flexible type extension
ext1 :: (Data a, Typeable t)
     => c a
     -> (forall d. Data d => c (t d))
     -> c a
ext1 def ext = maybe def id (dataCast1 ext)
ext1 :: (Data a, Typeable t)
     => c a
     -> (forall d. Data d => c (t d))
     -> c a
ext1 def ext = maybe def id (dataCast1 ext)
ext1 def ext = maybe def id (dataCast1 ext)