Stop writing Python in TypeScript.

@dataclass
class Circle:
    radius: float

@dataclass
class Rect:
    width: float
    height: float

def area(s):
    if isinstance(s, Circle):
        return pi * s.radius ** 2
    return s.width * s.heightclass Circle {
  constructor(public radius: number) {}
}
class Rect {
  constructor(
    public width: number,
    public height: number,
  ) {}
}
function area(s: Circle | Rect): number {
  if (s instanceof Circle)
    return Math.PI * s.radius ** 2;
  return s.width * s.height;
}type Circle = { kind: "circle"; radius: number };
type Rect = {
  kind: "rect";
  width: number;
  height: number;
};

function area(s: Circle | Rect): number {
  if (s.kind === "circle")
    return Math.PI * s.radius ** 2;
  return s.width * s.height;
}type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "rect"; width: number; height: number };

function area(s: Shape): number {
  switch (s.kind) {
    case "circle":
      return Math.PI * s.radius ** 2;
    case "rect":
      return s.width * s.height;
  }
}