Major Description
json4s is bound to become a dependency problem for the livy repl at some point, since Spark may be dropping it or upgrading to an incompatible version to support new Scala. Since json4s doesn't provide any functionality that cannot be re-implemented with Jackson, we should consider just using Jackson instead.
json4s also brings in some rather large transitive dependencies such as scala-compiler, which are not needed by anything else in Livy.