match.ts

function match<T, S>(value: T) {
  let result: ()=>S;
  const context = {
    caseOf(fn:(value: T) => boolean, payload: ()=>S) {
      if (!result && fn(value)) result = payload;
      return context;
    },
    _(payload: ()=>S) {
      if (!result) result = payload;
      return context;
    },
    resolve(): S {
      return result();
    }
  };
  return context;
}

const result = match<number, String>(123)
  .caseOf(w => w > 200, () => "A")
  .caseOf(w => w < 200, () => "B")
  .caseOf(w => w < 200, () => "C")
  ._(() => "D") // wildcard
  .resolve(); // "B"