> 2) Currently each JVM language has its own incompatible reinvention of closures.
Yeah, but as long as they expect Callables in the right place interop can be pretty easy with just interfaces. For instance, you can pass JRuby lambdas to Clojure functions just fine. Sure there's a duplication of effort, but it's not too bad for interop purposes.
Have you looked at the source code for that project? It doesn't use callables at all. the orig_commute function, the original commute method on class Ref, gets passed a monkey-patched ruby Proc object that implements the invoke method which takes one argument, a list, containing all of the original ruby arguments. Clojure then most likely calls invoke inside orig_commute through reflection. The end result: a bunch of hackery specific to Ruby and Clojure, something JVM-level closures would help eliminate.
Again, you cannot pass a ruby function expecting arguments to Clojure! What your link shows is that you can, however, send monkey-patched versions of ruby functions that implement clojure-specific calling conventions to clojure. :)