I have noticed that there can be two scala REPL in one JVM and you can even connect a Scala REPL remotely to a running JVM. So I was just wondering, how many REPLs can you have in one JVM, and what is it bounded by?
It depends on how far you would like to go to achieve it. Technically I don't think there is any hard limit except for memory. Production grade application web servers (such as Tomcat) can run pretty much any code in a well-isolated environment inside single JVM (using custom ClassLoaders among other tricks). They obviously can run several copies of the same application.