> especially now that they've added HKTs

Hmm .. as far as I'm aware, they haven't added this yet: https://github.com/microsoft/TypeScript/issues/1213

Note that higher-kinded types (though I'd rather call it "higher-kinded polymorphism" or something—type-level functions are not really types) would allow code similar to this:

  function foo<F, A>(f: (v: A) => F<A>, v: A): F<A> {
      return f(v);
  }