e48d4e1a ​

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