`either { }` is already a monad transformer becaus...

# arrow

[pakoito]

either { } is already a monad transformer because it allows suspend functions inside 😱

[julian]

@pakoito I thought transformers work with nested monads. What are the nested monads in this case?

[pakoito]

IO<Either<E, A>> is suspend fun bla(): Either<E, A> . So it’s nested and not immediately composable

[pakoito]

bla().flatMap {
  bla() // cannot call suspend functions inside flatMap
}

[pakoito]

unless you introduce support inline/suspend on the either declaration

[pakoito]

so it becomes EitherT<suspend, E, A>

[pakoito]

either {
  bla().bind()
  bla().bind()
}

[julian]

Thanks, @pakoito .
Were you using EitherT<suspend, E, A> to illustrate, or you meant it literally?

[julian]

Also, can you explain a bit what you mean by "not immediately composable"?

[pakoito]

to illustrate, yes

[pakoito]

Also, can you explain a bit what you mean by “not immediately composable”?

bla().flatMap {
  bla() // cannot call suspend functions inside flatMap
}

that’s one example

[pakoito]

suspend fun somethig() {
  val a: Either<Int, Int> = bla()
  val b: Either<Int, Int> = bla()
}

you don’t have a function to easily sequence one after another and shortcircuit on failure, if you prefer to see it this way

[pakoito]

unless you make flatMap support suspend inside, either directly accepting a suspend lambda or via inline (which is a bad hack IMO)

[pakoito]

the same way different monad types are not immediately composable, i.e. Either with Option, or IO with Observable, you cannot combine Either with Suspend

[pakoito]

or Suspend with Compose for that matter 😛

[julian]

Thanks @pakoito

[julian]

unless you make flatMap support suspend inside, either directly accepting a suspend lambda or via inline (which is a bad hack IMO)

Is this referring to making flatMap inline?