vendingMachineGeneric.ts

// TypeScript

// Types
type P = { readonly tag: "P" };
type Q = { readonly tag: "Q" };
type R = { readonly tag: "R" };

type Theorem = (h: (p: P) => (q: Q) => R) => ((hpq: { left: P; right: Q }) => R);

// Theorem
const theorem: Theorem = (h) => {
  return function (hpq) {
    return h(hpq.left)(hpq.right);
  };
}

// We could have also used tuple type as well for hpq: [P,Q]