ParseJson

I need to parse some JSON, since it's an operation that can fail we use Either<E,A>

import { pipe } from "fp-ts/lib/pipeable";
import * as E from "fp-ts/lib/Either";
import * as A from "fp-ts/lib/Apply";

const dataToBeParsed = JSON.stringify({ firstJson: true });

pipe(
  E.parseJSON(dataToBeParsed, E.toError),
  E.fold(
    e => console.log(e),
    data => console.log(data)
  )
);
// {"firstJson":true}

What if I have two JSON to parse?

Here we can use Chain and Map in a naive way

import { pipe } from "fp-ts/lib/pipeable";
import * as E from "fp-ts/lib/Either";
import * as A from "fp-ts/lib/Apply";

const dataToBeParsed = JSON.stringify({ firstJson: true });
const secondDataToBeParsed = JSON.stringify({
  thisIsTheSecondJson: "Yes it is"
});

pipe(
  E.parseJSON(dataToBeParsed, E.toError),
  E.chain(one =>
    pipe(
      E.parseJSON(secondDataToBeParsed, E.toError),
      E.map(two => [one, two])
    )
  ),
  E.fold(
    e => console.log(e),
    data => console.log(data)
  )
);
// [{"firstJson":true},{"thisIsTheSecondJson":"Yes it is"}]

As you can see this does not scale very well so we can use SequenceT to have the Eitheras arguments and parse the two JSON

import { pipe } from "fp-ts/lib/pipeable";
import * as E from "fp-ts/lib/Either";
import * as A from "fp-ts/lib/Apply";

const dataToBeParsed = JSON.stringify({ firstJson: true });
const secondDataToBeParsed = JSON.stringify({
  thisIsTheSecondJson: "Yes it is"
});

const sequenceE = A.sequenceT(E.either);

pipe(
  sequenceE(
    E.parseJSON(dataToBeParsed, E.toError),
    E.parseJSON(secondDataToBeParsed, E.toError)
  ),
  E.fold(
    e => console.log(e),
    data => console.log(data)
  )
);

//[{"firstJson":true},{"thisIsTheSecondJson":"Yes it is"}]

You can find the code for this example here in the example.ts file