Comment by ts0000

In addition to the other TypeScript examples, here's one that I would actually use. Now, it's not encoding the types not as positional, but named arguments via objects. Allows me to destructure them, for added clarity.

  type Circle = {x: number; y: number; r: number};
  type Rectangle = {x: number; y: number; w: number; h: number};
  
  type Shape = <T>(xs: {
      circle: (args: Circle) => T;
      rectangle: (args: Rectangle) => T;
  }) => T;
  
  function Circle(x: Circle): Shape {
      return ({circle}) => circle(x);
  }
  
  function Rectangle(x: Rectangle): Shape {
      return ({rectangle}) => rectangle(x);
  }
  
  const exampleCircle = Circle({x: 2, y: 1.4, r: 4.5});
  const exampleRectangle = Rectangle({x: 1.3, y: 3.1, w: 10.3, h: 7.7});
  
  const area = (shape: Shape): number =>
      shape({
          circle: ({r}: Circle) => Math.PI * r * r,
          rectangle: ({w, h}: Rectangle) => w * h,
      });
  
  console.log(area(exampleCircle));
  console.log(area(exampleRectangle));

/edit: Fixed formatting. /edit: Clarify something.