:wave: To concatenate two `Option<Nel<Stuff>>` we where using `Semigroup.option(Semigr...

# arrow

[Giulio Caccin]

👋 To concatenate two Option<Nel<Stuff>> we where using Semigroup.option(Semigroup.nonemptylist<Stuff>()) , now i’m bumping Arrow version and I wanted to try using null as much as possible. Is there any elegant way to use semigroup to concatenate NonEmptyList<Stuff>?

[CLOVIS]

Can't you just list1?.plus(list2) ?

[CLOVIS]

Oh, no, because list2 could be empty

Then:

operator fun <T> NonEmptyList<T>?.plus(other: NonEmptyList<T>?): NonEmptyList<T>? {
    val first = this ?: return null
    val second = this ?: return null

    return first + second
}

[Giulio Caccin]

yes i could, and we did somewhere, but that function is also inside maybeCombine of the semigroup, and i was asking because i thought there was a way to use semigroups for that

[Giulio Caccin]

In the end I could not find anything better then:

operator fun <T> NonEmptyList<T>?.plus(other: NonEmptyList<T>?) =
    Semigroup.option(Semigroup.nonEmptyList<T>()).run {
        [e-mail]() + other.toOption()
    }.orNull()

[CLOVIS]

Out of curiosity, why are you using nullable NonEmptyList s?

[CLOVIS]

NonEmptyList +`null` is isomorphic with just List , isn't it?

[Giulio Caccin]

I understand your seciquestion