Get Value from a IOEither example

[seyfer]

Hey!

If I use getOrElse on IOEither I have to provide IO type value as a Left result, cannot be just null.

What I do now, I convert IOEither to TaskEither with fromIOEither function and then just run and await for TaskEither.
But that makes the whole pipe async. Any other way to get a value from IOEither without async?

[Punie]

Hello 🙂

First, sorry for the delay, I somehow completely missed your issue 😞
I still hope you'll find the (late) answer useful.

If I understand correctly, you are trying to do the following:

pipe(
  someIOEither,
  IOEither.getOrElse(() => null),
  ...do something with the A | null from the IOEither
)

And because it doesn't work, you are going through the trouble of converting your IOEither to a TaskEither (I assume because you are more comfortable with the latter?) which makes your computation async.

The problem you are having is that IOEither<E, A> is just sugar for IO<Either<E, A>> and the getOrElse only applies to the inner Either, collapsing the whole thing into an IO<A> that you can then just run like any other IO.

I think you then have two options:

• use getOrElseW (the W is important as you extend the A with null) and then run the IO:

pipe(
  someIOEither,
  IOEither.getOrElseW(() => IO.of(null)), // <= notice that you have to provide null wrapped in an IO, hence the IO.of(...)
  ...do something with the resulting IO<A | null>,
)() // <= run the IO to get the result

• first run the IO and getOrElse the resulting Either<E, A>:

pipe(
  someIOEither(), // <= run the IO immediately
  Either.getOrElseW(() => null), // <= notice we use Either<E, A> instead of IOEither<E, A> as the IO is already performed
  ...do something with the resulting A | null,
)

I hope that makes sense, please don't hesitate to reach out again if that wasn't clear enough 🙂