generics.js

import {sample, sampleOne, types} from 'babel-plugin-transform-flow-to-gen/api';
import type {Animal, Dog} from './types';

const dogGen = Animal(types.literal('dog'));
const anySpeciesGen = Animal(types.string());

const dog = sampleOne(dogGen);

console.log(dog);
// { "species": "dog", "name": "ahKL9p" }

console.log(Dog());
// { "species": "dog", "name": "1c" }

types.js

export type Animal<T> = {
  species: T,
  name: string
}

export type Dog = Animal<'dog'>;

export type AnySpecies = Animal<string>;