thing-i-save.js

const Future = require('fluture');
const R = require('ramda');
const {Reader} = require('monet');

const FakeDb = () => {
  const data = {
    1: {id: 1, name: 'bob', bff: 2},
    2: {id: 2, name: 'alice', bff: 1}
  };

  return { byId: id => Promise.resolve(data[id]) };
};
const upperName = data => data.name.toUpperCase();
const getUser1 = Reader(db => db.byId(1));
const getBestFriend = data => Reader(db => db.byId(data.bff));

const ReaderPromise = value => {
  const map = fn => ReaderPromise(
    value.map(
      promise => promise.then(fn)
    )
  );
  const chain = fn => ReaderPromise(
    value.chain(
      promise => Reader(
        config => promise.then(
          (...args) => fn(...args).run(config)
        )
      )
    )
  );

  return Object.freeze({chain, map, run: (config) => value.run(config)});
}

const program = ReaderPromise(getUser1)
  .chain(data => ReaderPromise(getBestFriend(data)))
  .map(upperName)

program.run(FakeDb()).then(console.log);