Possible solution for run h $ line [[1, 2],[3,4],[5,6]] :: IO Line

line.hs

-- Looks like run h $ line [[1,2],[3,4],[5,6]] :: IO Line was not matching on Array v so was falling to mempty
-- This solution return (in Show form) fromList [LonLat 1 2,LonLat 3 4,LonLat 5 6]
instance FromDatum a => FromDatum (Vector a) where
  parseDatum (Array v) = fmap V.fromList . mapM parseDatum $ V.toList v
  parseDatum (Line l) = fmap V.fromList . mapM (parseDatum . toDatum) $ V.toList l
  parseDatum _ = mempty