How to Aggregate Errors on Tasks?

This is a use case I haven’t been able to solve.

I have 3 http requests, if one fails, I want, at least, the result of the other 2. Ideally, I would want to know what error happened.

I’m still using data.task from folktale 1, and this is how I do the requests, which fails fast (if one fails, I only get the first error with no result):

const mergeResults = data => logs => customer => ({ data, logs, customer })

liftA3(
  mergeResults,
  getDataFromAPI(userId),
  getLogs(userId),
  getCustomer(customerID)
).fork(
   error => ... Handle the first thrown error,
   result => ... All 3 requests succeeded here
)

Here, I would like to have data and logs returned if getCustomer API call fails. Thanks in advance

[robotlolita]

Oh! So you want individual results rather than the overall results. That’s easier.

With:

const Task = require('data.task');
const Validation = require('data.validation');
const { parallel } = require('control.async')(Task);

const toTaskOfValidations = (task) =>
  task.map(Validation.of)
      .orElse(error => Task.of(Validation.Failure(error)));

const runEach = (tasks) =>
  parallel(tasks.map(toTaskOfValidations));

And use it as:

const getDataFromAPI = a => Task.of('data');
const getLogs = b => Task.rejected('logs');
const getCustomer = c => Task.rejected('customer');

const mergeResults = (data, logs, customer) => ({ data, logs, customer });

const userId = 1;

runEach([
  getDataFromAPI(userId),
  getLogs(userId),
  getCustomer(userId)
]).map(xs => mergeResults(...xs))
  .fork(
    error => /* never happens */,
    value => console.log(value)
  );

Here each value of the results record will be a Validation, however, so you’ll need to pattern match on whether each individual result is a failure or a success.

[diasbruno]

Sorry for suddenly jump in. I’ve recently needed something like this, but with plain promises.