uniontypeflow.js

/* @flow */

// daggy.tagged(arguments)
//declare module 'daggy' {
  declare function tagged<T>(...args: string[]): (...xs: Array<T>) => {[k: string]: T};
//}
//import daggy from 'daggy';

var Tuple3 = tagged('x', 'y', 'z');

var _123 = Tuple3(1, 2, 3); // optional new keyword
_123.x == 1 && _123.y == 2 && _123.z == 3; // true
_123 instanceof Tuple3 == true; // true

type Caser<T> = (cs: {[k: $Keys<T> | '_']: Function}) => any
type Caser2 = (cs: {_: Function}) => any

declare function Type<T>(types: T): { case: Caser<T>, [k: $Keys<T>]: Function }

const types = Type({
  Foo: [],
  Bar: [],
});

types.Foo();
types.Bar(1);
// types.Bill();
types.case({
  Foo: () => null,
  Bar: () => 1,
  _: () => null,
});