But if the calling and stack semantics are different from Java's (and the kind of have to be), than you can't just merge the ASTs. Ruby, provided you don't impl

But if the calling and stack semantics are different from Java's (and the kind of have to be), than you can't just merge the ASTs. Ruby, provided you don't implement callcc, is almost, if not entirely identical in calling convention to C. So if truffle supports magical AST merging, as described, I don't think you can implement anything with a different set of conventions to C/Java.