ea32f347 ​

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