Thanks for the comment, Dimitre. Yes, I'll look into this. I need to think carefully about the implications for type-checking. It might just fall out, I'm not sure. (I think that if any run-time checking of the result of a function body is needed, then the function isn't tail-recursive by definition; so perhaps it's OK.) The only other difference is that the stack frame may need to be resized, and the stack frame map used by debuggers needs to be switched.