hi, has anyone of you guys made a comparison of functional aspects of Java+Vavr vs. Kotlin? What are your feelings? Or is Kotlin and Vavr complementing each other?

I feel for functional Kotlin you need to take a loot at arrow-kt: https://arrow-kt.io/

To reply directly to your question, Java+Varv has lots of stuff that's not in Kotlin by default, but indeed #arrow is the way to go and for persistent collections there's this official project coming up: https://github.com/Kotlin/kotlinx.collections.immutable