function generatorBless(generator) {
  generator.map = generatorProtoMap;
  generator.flatmap = generatorProtoFlatMap;
  generator.flatMap = generatorProtoFlatMap;
  return generator;
}
- `generator.bless(f: nat -> a): generator a`

      Bless function with `.map` and `.flatmap` properties.

  - `.map(f: a -> b): generator b`

      Map `generator a` into `generator b`. For example:

      ```js
      positiveIntegersGenerator = nat.generator.map(
        function (x) { return x + 1; });
      ```

  - `.flatmap(f: a -> generator b): generator b`

      Monadic bind for generators. Also `flatMap` version is supported.