a61f2674 ​

input = fill 9v (fill 9h black) |> fold (λr. rect ((r.1, r.2, 9v, r.2), grey)) #0
output = fill 9v (fill 9h black) |> rect ((#1.1, #1.2, 9v, #1.3), red) |> rect ((#2.1, #2.2, 9v, #2.3), blue)
(UList (VInt, HInt), (VInt, HInt, HInt), (VInt, HInt, HInt))
({(7v, 9h), (6v, 5h), (4v, 1h), (3v, 7h), (2v, 3h)}, (7v, 9h, 9h), (2v, 3h, 3h))
({(8v, 3h), (4v, 7h), (3v, 1h), (1v, 5h)}, (8v, 3h, 3h), (1v, 5h, 5h))
({(9v, 2h), (5v, 6h), (3v, 4h), (2v, 8h)}, (?, ?, ?), (?, ?, ?))