IO monad example in typescript

IOMonad.ts

interface IO<T> {
   (unsafeIO: Function): IO<T>; 
   chain(fn: (a: T) => IO<T>): IO<T>
   of(performUnsafeIO: (a: T) => T): IO<T>;
   fork(): IO<T>;
   map(fn: (a: T) => T): IO<T>;
   value: Function
};
type KIO<T> = (a: T) => T;
type FIO<T> = (a: T) => IO<T>;

function IO<T>(this: IO<T>, unsafeIO: (Function)) {
  this.value = unsafeIO;
  return this;
};

IO.prototype.chain = function<T>(fn: FIO<T>) {
  return fn(this.value())
}

function new_(x: any, k: any) {
  return new x(k);
}

IO.of = function<T>(performUnsafeIO: KIO<T>): IO<T> {
  return new_(IO, performUnsafeIO);
}

IO.prototype.fork = function() {
  return new_(IO, this.value());
}

IO.prototype.map = function(fn: Function) {
  return new_(IO, () => fn(this.value()))
}


// USAGE

const fn: ((a: number) => number) = a => a + 1.0;
const gn: ((a: number) => string) = g => g + "1.0";
const a = IO.of(() => Math.random()).map(fn).map(a => a * 2).chain(p => IO.of(fn)).chain((k) => IO.of(() => Math.random() + k)).fork()


console.log(a);