Binary = Patch {0, 1}
Binary.
    invert self =
        if self == 0, 1 else 0
assert 1.invert() == 0
assert 0.invert() == 1

Nat = Patch {I | I >= 0}
Nat.times! self, block! =
    for! 0..<self, _ => block!()
10.times! do!:
    print! "!"