_: {"a", "b", "c"} = "a" # OK
_: {"a", "b", "c"} = "d" # ERR

# 1..12 == {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12} as type
_: 1..12 = 1 # OK
_: 1..12 = 13 # ERR

Suite = Class { "Heart", "Spade", "Club", "Diamond" }
Suite.
    is_heart self = self::base == "Heart"
Number = Class 1..13
Number.
    is_ace self = self::base == 1
Card = Class { .suite = Suite; .number = Number }
Card.
    from_str_and_num suite: Str, num: Nat =
        assert suite in {"Heart", "Spade", "Club", "Diamond"}
        assert num in 1..13
        Card.new { .suite = Suite.new suite; .number = Number.new num }
    is_ace_of_heart self = self.suite.is_heart() and self.number.is_ace()

c = Card.new { .suite = Suite.new "Heart"; .number = Number.new 1 }
assert c.is_ace_of_heart()

Nat8 = Inherit 0..255
Nat8.
    as_ascii self = chr self
    satuating_add self, other: Nat =
        if self + other >= 0 and self + other <= 255:
            do: Nat8.new self + other
            do: Nat8.new 255

n = Nat8.new 97
_: Nat = n + 2
assert n.as_ascii() == "a"
assert n.satuating_add(300) == 255