444801d8 ​

input = fill 10v (fill 10h black) |> fold (fold rect) #0
output = fill 10v (fill 10h black) |> fold (λr. rect ((r.2, r.3 + 4 - 4 | r.3, r.4, r.3 + 4), r.1)) #1 |> fold (λr. rect (r, blue)) #2
(OList UList ((VInt, HInt, VInt, HInt), Color), UList (Color, VInt, HInt, VInt), UList (VInt, HInt, VInt, HInt))
([{((2v, 5h, 2v, 6h), blue), ((2v, 6h, 6v, 6h), blue), ((6v, 2h, 6v, 6h), blue), ((2v, 2h, 6v, 2h), blue), ((2v, 2h, 2v, 3h), blue), ((4v, 4h, 4v, 4h), red)}], {(red, 1v, 2h, 5v)}, {(2v, 5h, 2v, 6h), (2v, 6h, 6v, 6h), (6v, 2h, 6v, 6h), (2v, 2h, 6v, 2h), (2v, 2h, 2v, 3h)})
([{((9v, 6h, 9v, 8h), black), ((4v, 3h, 5v, 5h), black)}, {((8v, 8h, 8v, 9h), blue), ((8v, 9h, 10v, 9h), blue), ((10v, 5h, 10v, 9h), blue), ((8v, 5h, 10v, 5h), blue), ((8v, 5h, 8v, 6h), blue), ((3v, 5h, 3v, 6h), blue), ((3v, 6h, 6v, 6h), blue), ((6v, 2h, 6v, 6h), blue), ((3v, 2h, 6v, 2h), blue), ((3v, 2h, 3v, 3h), blue), ((9v, 7h, 9v, 7h), green), ((4v, 4h, 4v, 4h), red)}], {(green, 7v, 5h, 9v), (red, 2v, 2h, 5v)}, {(8v, 8h, 8v, 9h), (8v, 9h, 10v, 9h), (10v, 5h, 10v, 9h), (8v, 5h, 10v, 5h), (8v, 5h, 8v, 6h), (3v, 5h, 3v, 6h), (3v, 6h, 6v, 6h), (6v, 2h, 6v, 6h), (3v, 2h, 6v, 2h), (3v, 2h, 3v, 3h)})
([{((9v, 6h, 9v, 8h), black), ((3v, 3h, 4v, 5h), black)}, {((8v, 8h, 8v, 9h), blue), ((8v, 9h, 10v, 9h), blue), ((10v, 5h, 10v, 9h), blue), ((8v, 5h, 10v, 5h), blue), ((8v, 5h, 8v, 6h), blue), ((2v, 5h, 2v, 6h), blue), ((2v, 6h, 5v, 6h), blue), ((5v, 2h, 5v, 6h), blue), ((2v, 2h, 5v, 2h), blue), ((2v, 2h, 2v, 3h), blue), ((9v, 7h, 9v, 7h), teal), ((3v, 4h, 3v, 4h), fuschia)}], {(teal, 7v, 5h, 9v), (fuschia, 1v, 2h, 4v)}, {(8v, 8h, 8v, 9h), (8v, 9h, 10v, 9h), (10v, 5h, 10v, 9h), (8v, 5h, 10v, 5h), (8v, 5h, 8v, 6h), (2v, 5h, 2v, 6h), (2v, 6h, 5v, 6h), (5v, 2h, 5v, 6h), (2v, 2h, 5v, 2h), (2v, 2h, 2v, 3h)})
([{((8v, 6h, 9v, 8h), black), ((3v, 2h, 4v, 4h), black)}, {((7v, 8h, 7v, 9h), blue), ((7v, 9h, 10v, 9h), blue), ((10v, 5h, 10v, 9h), blue), ((7v, 5h, 10v, 5h), blue), ((7v, 5h, 7v, 6h), blue), ((2v, 4h, 2v, 5h), blue), ((2v, 5h, 5v, 5h), blue), ((5v, 1h, 5v, 5h), blue), ((2v, 1h, 5v, 1h), blue), ((2v, 1h, 2v, 2h), blue), ((8v, 7h, 8v, 7h), orange), ((3v, 3h, 3v, 3h), yellow)}], ?, ?)