// An optional integer value.
type OptionalInt = union {
    Some: int;
    None: unit
};

fun displayOption(o: OptionalInt): unit =
    match o with {
        Some{x} -> println(x);
        None{_} -> println("None")
    };

displayOption(Some{42});
displayOption(None{()});

// A shape type.
type Shape = union {
    Circle: struct { radius: float };
    Rectangle: struct { width: float; height: float };
    Square: struct { side: float }
};

// Return the area of a shape.
fun area(s: Shape): float =
    match s with {
        Circle{c} -> c.radius * c.radius * 3.14f;
        Rectangle{r} -> r.width * r.height;
        Square{s} -> s.side * s.side
    };

assert(area(Circle{struct {radius = 2.0f}}) = 12.56f);
assert(area(Rectangle{struct {width = 2.0f; height = 3.0f}}) = 6.0f);
assert(area(Square{struct {side = 5.0f}}) = 25.0f)