A really simple solution in that case is to run JRuby and then write computationally intensive code in a JVM compatible lang like Scala or Clojure. This route seems popular since you can easily give JRuby access to your Scala classes.
Right, but if already writing in Scala, why ever write some parts of code in Ruby? Scala gets you expressivity of Ruby with additional benefit of static typesafety.
Well a pretty typical scenario is you are writing a ruby app and run into an area that needs additional horsepower (say a gaming API or something). Being on JRuby would give you more options at that point.
