Map a given function onto a set and union the resulting set.

neighbors :: (Int, Int) -> Set (Int, Int)
neighbors (x, y) =
    Set.fromList
      [ (x - 1, y - 1), (x, y - 1), (x + 1, y - 1)
      , (x - 1, y),                 (x + 1, y)
      , (x - 1, y + 1), (x, y + 1), (x + 1, y + 1)
      ]
Set.Extra.concatMap neighbors setOfPoints

Check if a Set is a subset of another Set.

Set.Extra.subset (Set.fromList [1,2,3]) (Set.fromList [1,2,3,4,5]) -- True