task_spec.js

import Task from 'data.task';
import R from 'ramda';

const run = t => {
  return t.fork(
    err => console.log('err', err),
    R.tap(console.log)
  );
}

// Will run Identity on an object prop
const idProp = key => R.pipe(
  R.prop(key),
  R.identity
);


// Will chain on an object prop
const chainProp = R.curry((key, fn) => R.pipe(
  R.prop(key),
  R.chain(fn)
));

// Will take an object spec and  return a Task
// that will resolve to an object of the same shape
// with each underlying Task resolved
//
// basically considering an object as a traversable and runing all Task in parallel
const assembleSpec = (spec) => {
  const arrSpec = R.toPairs(spec);
  const results = [];

  let rejected = false;
  let finishedAll = false;

  return new Task((reject, resolve) => {

    arrSpec.forEach(([key, task]) => {
      task.fork(guardReject, guardResolve(val => {
        results.push([key, val]);
        if (results.length === arrSpec.length) finishedAll = true;
      }));
    });

    function guardResolve(setter) {
      return x => {
        if (rejected) return;

        setter(x);
        if (finishedAll) return resolve(R.fromPairs(results));

        return x;
      }
    }

    function guardReject(x) {
      if (!rejected) {
        rejected = true;
        return reject(x);
      }
    }
  });
};


const getContact = id => new Task((_, resolve) => resolve({id}));

const createEntity = R.curry((payload, user, contact) => {
  return new Task((_, resolve) => {
    setTimeout(() => {
      resolve({
        ...payload,
        id: 1,
        contactId: contact.id,
        userId: user.id
      });
    }, 1000);
  });
});


const payload = {
  field1: 'value of field 1'
};
const user = {
  id: 666
};

const updateContact = contact => {
  return new Task((_, resolve) => {
    resolve({
      ...contact,
      isActive: true,
    });
  });
}

const prog = R.pipe(
  getContact,
  R.applySpec({
    contact: R.identity,
    beuz: R.chain(createEntity(payload, user)),
  }),
  R.applySpec({
    contact: chainProp('contact', updateContact),
    beuz: idProp('beuz'),
  }),
  assembleSpec
)(10);

run(prog);