Here's a quote from Reynolds, one of the creators of Spark:
> The primary issue I can think of comes from the lack of pattern matching. Kotlin’s language designer left out pattern matching intentionally because it is a complex feature whose use case is primarily for building compilers. However, modern Spark (post Catalyst / Tungsten) look a lot like compilers and as a result the internals would become more verbose if built using a language that doesn't support pattern matching.
> The primary issue I can think of comes from the lack of pattern matching. Kotlin’s language designer left out pattern matching intentionally because it is a complex feature whose use case is primarily for building compilers. However, modern Spark (post Catalyst / Tungsten) look a lot like compilers and as a result the internals would become more verbose if built using a language that doesn't support pattern matching.
Source: https://www.quora.com/profile/Reynold-Xin