Hi everyone, I had a use case recently where I had to return left in an either if the right value wa...

# arrow

[gabib]

Hi everyone, I had a use case recently where I had to return left in an either if the right value was not null. So I ended up writing an extension function for that:
inline fun <E, B> Either<E, B?>.leftIfNotNull(f: () -> E): Either<E, Nothing?> = flatMap { it.rightIfNull { f() } }
Is there something that might have helped in Arrow and I've missed it?

[thanh]

If you use either effect, I usually use this pattern

fun loadValue(): Either<Error, Value?> = TODO()
either {  
  val valueOrNull = loadValue().bind()
  val value = ensureNotNull(valueOrNull) { ValueNotFound }
}

[gabib]

So in my case it would be something like this

ensure(valueOrNull == null) { "Value already exists" }

Thank you