Hello, I was thinking about the integration of lisp and java with abcl and it struck me that we don't have an easy way to pass a callback from Java to Lisp (e.g. a function acting as a factory of objects): one can extend Function, Primitive or even LispObject and implement the appropriate execute() method overload; however, one must perform conversion to/from Lisp objects manually, and while this is a minor inconvenience, it adds boilerplate code that could be easily avoided. So I was thinking about adding a Callback class extending Function, with overloads for execute() taking and returning regular java.lang.Object instances, and corresponding execute() based on LispObjects that perform the necessary conversions and call the Java-friendly versions. Example: public LispObject execute(LispObject arg0) { return JavaObject.getInstance(execute(arg0.javaInstance())); } /** To be overridden by the implementing subclass */ protected Object execute(Object arg0) { return error(new WrongNumberOfArgumentsException(this)); } Such a class could have convenience factory methods taking Runnables, Callables and other popular kinds of Java callback objects. Thoughts? Ale