async-await.js

(function () {

  const Promise = require('Promise');

  const wrap_gen = g =>
    ({
      next: () => {
        try {
          const value = g.next();
          if (value.done) {
            return value;
          }
          return {
            done: false,
            value: value,
          };
        }
        catch (e) {
          return { done: true };
        }
      },
    });

  const g_return = value =>
    ({ done: true, value: value });

  const awaiter = g => new Promise(resolve => {
    let fulfilled_value;
    const fulfilled = value => {
      fulfilled_value = value;
      step(g.next());
    };
    const step = result => {
      result.done ?
        resolve(result.value) :
        new Promise(resolve => { resolve(result.value); }).then(fulfilled);
    };
    g = g(() => fulfilled_value);
    step(g.next());
  });

  const async = g =>
    awaiter(rv => wrap_gen(g(rv)()));

  module.exports = {
    async: async,
    g_return: g_return,
  };

})();