extractNl :: Node.List               -- ^ The original node list
          -> Maybe Node.AllocElement -- ^ The result of the allocation attempt
          -> Node.List               -- ^ The new node list
extractNl nl Nothing = nl
extractNl :: Node.List               -- ^ The original node list
          -> Maybe Node.AllocElement -- ^ The result of the allocation attempt
          -> Node.List
extractNl nl Nothing = nl
extractNl nl Nothing = nl