discriminatedUnionsWithMatch.ts

interface DemoEnumPatternMap<T> {
  Foo: (foo: Foo) => T,
  Bar: (bar: Bar) => T
}

function matchDemoEnum<T>(value: DemoEnum, pattern: DemoEnumPatternMap<T>) : T {
  switch (value.kind) {
    case "Foo":
      return pattern.Foo(value);
    case "Bar":
      return pattern.Bar(value);
  }
}

for (const value of values) {
  matchDemoEnum(value, {
    Foo: ({ n }) => console.log(`Encountered a Foo with n: ${n}`),
    Bar: ({ s }) => console.log(`Bar came with a message: ${s}`)
  });
}