I’ll start a new thread related to what <@U0B8UEMV1> suggested on <here>.

# arrow-contributors

[pablisco]

I’ll start a new thread related to what @pakoito suggested on here.

[pablisco]

Would it make sense to have shortcut bindings? We may be able to save having to create an Either if not needed. Something like:

leftValue.bindLeft()
rightValue.bindRight()

And potentially the same for other types:

nullable.bindOr { fallbackLeft }
option.bindOr { fallbackLeft }
result.bindOr { e -> someOtherLeftFrom(e) }

[simon.vergauwen]

I’m actually really looking forward to multiple receivers

[simon.vergauwen]

Not sure if it’s relevant here but I often find myself wanting to use it in production projects

[simon.vergauwen]

To enhance the Either DSL in cool ways

[pablisco]

Until we have MR, I’m trying to create this to provide similar restrictions that we can use to create a nicer API 🙂

[simon.vergauwen]

I tried looking into the repo, but didn’t grasp the functionality yet I think 😅 Add a readme 😜

[pablisco]

Yeah, it was just an intial try to use Meta 😅
The target functionality for the first prototype is defined here. Means that we can define custom Scope annotations. These can be used to tell the compiler that they can only be run on other functions annotated with that same annotation.
Additionally, I would like to add some scope aware storage to share dependencies. Potentially typesafe 🤞

[simon.vergauwen]

Ah okay, got it 👍 That is pretty cool for special DSLs, kinda like RestrictSuspension but without limiting suspension

[Marc]

I’m sorry for my ignorance but what cases are you thinking MR would be beneficial for? (any example?)

[simon.vergauwen]

You can basically add domain specific DSLs to either, or have access to bind without wrapping in either { }.
Here ensureNotNull comes from either { }, and this function can only be called inside either<MyError, A> but potentially you can write your whole domain code like this without having Either in the return type.

@Context(EitherEffect<MyError, Any?>)
suspend fun ProductRepo.fetchUsers(): List<User> =
  ensureNotNull(fetch("SQL QUERY")) { MyError("Users not found") }

[simon.vergauwen]

Or when you want to enable special DSLs because you typically want to enable special extension on Either<E, A> but you also want access to the EitherEffect<E, Any?>.
So currently we can only add special functions for the DSL inside Arrow Core but with multiple receivers you can add special DSL functions from outside the library also.

@Context(EitherEffect<E, Any?>)
suspend fun <E> Either<E, A>.customDSL(): A {
  val a = this.bind()
  // DSL logic
  a
}

either<E, A> {
   1.right().customDSL()
}

[Marc]

an what is a EitherEffect?

[simon.vergauwen]

EitherEffect is the receiver of the either { } dsl.

Here either<E, A> { this }, this is EitherEffect<E, Any?>

[simon.vergauwen]

That’s why you can only call customDSL inside either { }