$Gen.js

import uuid from 'uuid-v4';
import {sample} from 'babel-plugin-transform-flow-to-gen/api';
import type {$Gen} from 'babel-plugin-transform-flow-to-gen/Gen';

// FYI,
// type $Gen<T, _U> = T;

type User = {
  id: $Gen<string, uuid>, // $Gen only supports references to function calls
  name: string
}
  
console.log(sampleOne(User()));
// { "id": "90d53f1a-c49c-4010-aeaa-68d52e56181f", "name": "pnxR" }